Initial code from Manuel Bentele

kept unchanged for reference.

14 files changed, 5652 insertions, 0 deletions

diff --git a/Kconfig b/Kconfig
new file mode 100644
index 0000000..d227337
--- /dev/null
+++ b/Kconfig
@@ -0,0 +1,93 @@
+# SPDX-License-Identifier: GPL-2.0
+#
+# Loop device driver configuration
+#
+
+config BLK_DEV_LOOP
+	tristate "Loopback device support"
+	---help---
+	  Saying Y here will allow you to use a regular file as a block
+	  device; you can then create a file system on that block device and
+	  mount it just as you would mount other block devices such as hard
+	  drive partitions, CD-ROM drives or floppy drives. The loop devices
+	  are block special device files with major number 7 and typically
+	  called /dev/loop0, /dev/loop1 etc.
+
+	  This is useful if you want to check an ISO 9660 file system before
+	  burning the CD, or if you want to use floppy images without first
+	  writing them to floppy. Furthermore, some Linux distributions avoid
+	  the need for a dedicated Linux partition by keeping their complete
+	  root file system inside a DOS FAT file using this loop device
+	  driver.
+
+	  To use the loop device, you need the losetup utility, found in the
+	  util-linux package, see
+	  <https://www.kernel.org/pub/linux/utils/util-linux/>.
+
+	  The loop device driver can also be used to "hide" a file system in
+	  a disk partition, floppy, or regular file, either using encryption
+	  (scrambling the data) or steganography (hiding the data in the low
+	  bits of, say, a sound file). This is also safe if the file resides
+	  on a remote file server.
+
+	  There are several ways of encrypting disks. Some of these require
+	  kernel patches. The vanilla kernel offers the cryptoloop option
+	  and a Device Mapper target (which is superior, as it supports all
+	  file systems). If you want to use the cryptoloop, say Y to both
+	  LOOP and CRYPTOLOOP, and make sure you have a recent (version 2.12
+	  or later) version of util-linux. Additionally, be aware that
+	  the cryptoloop is not safe for storing journaled filesystems.
+
+	  Note that this loop device has nothing to do with the loopback
+	  device used for network connections from the machine to itself.
+
+	  To compile this driver as a module, choose M here: the
+	  module will be called loop.
+
+	  Most users will answer N here.
+
+config BLK_DEV_LOOP_MIN_COUNT
+	int "Number of loop devices to pre-create at init time"
+	depends on BLK_DEV_LOOP
+	default 8
+	help
+	  Static number of loop devices to be unconditionally pre-created
+	  at init time.
+
+	  This default value can be overwritten on the kernel command
+	  line or with module-parameter loop.max_loop.
+
+	  The historic default is 8. If a late 2011 version of losetup(8)
+	  is used, it can be set to 0, since needed loop devices can be
+	  dynamically allocated with the /dev/loop-control interface.
+
+config BLK_DEV_CRYPTOLOOP
+	tristate "Cryptoloop Support"
+	select CRYPTO
+	select CRYPTO_CBC
+	depends on BLK_DEV_LOOP
+	---help---
+	  Say Y here if you want to be able to use the ciphers that are
+	  provided by the CryptoAPI as loop transformation. This might be
+	  used as hard disk encryption.
+
+	  WARNING: This device is not safe for journaled file systems like
+	  ext3 or Reiserfs. Please use the Device Mapper crypto module
+	  instead, which can be configured to be on-disk compatible with the
+	  cryptoloop device.
+
+config BLK_DEV_LOOP_FILE_FMT_RAW
+	tristate "Loop device binary file format support"
+	depends on BLK_DEV_LOOP
+	---help---
+	  Say Y or M here if you want to enable the binary (RAW) file format
+	  support of the loop device module.
+
+config BLK_DEV_LOOP_FILE_FMT_QCOW
+	tristate "Loop device QCOW file format support"
+	depends on BLK_DEV_LOOP
+	select ZLIB_INFLATE
+	select ZLIB_DEFLATE
+	---help---
+	  Say Y or M here if you want to enable the QEMU's copy on write (QCOW)
+	  file format support of the loop device module.
diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..a82cd7a
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,11 @@
+# SPDX-License-Identifier: GPL-2.0
+
+loop-y						             += loop_main.o loop_file_fmt.o
+obj-$(CONFIG_BLK_DEV_LOOP)	             += loop.o
+
+obj-$(CONFIG_BLK_DEV_CRYPTOLOOP)         += cryptoloop.o
+
+obj-$(CONFIG_BLK_DEV_LOOP_FILE_FMT_RAW)  += loop_file_fmt_raw.o
+
+loop_file_fmt_qcow-y                     += loop_file_fmt_qcow_main.o loop_file_fmt_qcow_cluster.o loop_file_fmt_qcow_cache.o
+obj-$(CONFIG_BLK_DEV_LOOP_FILE_FMT_QCOW) += loop_file_fmt_qcow.o
diff --git a/cryptoloop.c b/cryptoloop.c
new file mode 100644
index 0000000..4d78436
--- /dev/null
+++ b/cryptoloop.c
@@ -0,0 +1,216 @@
+/*
+   Linux loop encryption enabling module
+
+   Copyright (C)  2002 Herbert Valerio Riedel <hvr@gnu.org>
+   Copyright (C)  2003 Fruhwirth Clemens <clemens@endorphin.org>
+
+   This module is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 2 of the License, or
+   (at your option) any later version.
+
+   This module is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this module; if not, write to the Free Software
+   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ */
+
+#include <linux/module.h>
+
+#include <crypto/skcipher.h>
+#include <linux/init.h>
+#include <linux/string.h>
+#include <linux/blkdev.h>
+#include <linux/scatterlist.h>
+#include <linux/uaccess.h>
+#include "loop_main.h"
+
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("loop blockdevice transferfunction adaptor / CryptoAPI");
+MODULE_AUTHOR("Herbert Valerio Riedel <hvr@gnu.org>");
+
+#define LOOP_IV_SECTOR_BITS 9
+#define LOOP_IV_SECTOR_SIZE (1 << LOOP_IV_SECTOR_BITS)
+
+static int
+cryptoloop_init(struct loop_device *lo, const struct loop_info64 *info)
+{
+	int err = -EINVAL;
+	int cipher_len;
+	int mode_len;
+	char cms[LO_NAME_SIZE];			/* cipher-mode string */
+	char *mode;
+	char *cmsp = cms;			/* c-m string pointer */
+	struct crypto_skcipher *tfm;
+
+	/* encryption breaks for non sector aligned offsets */
+
+	if (info->lo_offset % LOOP_IV_SECTOR_SIZE)
+		goto out;
+
+	strncpy(cms, info->lo_crypt_name, LO_NAME_SIZE);
+	cms[LO_NAME_SIZE - 1] = 0;
+
+	cipher_len = strcspn(cmsp, "-");
+
+	mode = cmsp + cipher_len;
+	mode_len = 0;
+	if (*mode) {
+		mode++;
+		mode_len = strcspn(mode, "-");
+	}
+
+	if (!mode_len) {
+		mode = "cbc";
+		mode_len = 3;
+	}
+
+	if (cipher_len + mode_len + 3 > LO_NAME_SIZE)
+		return -EINVAL;
+
+	memmove(cms, mode, mode_len);
+	cmsp = cms + mode_len;
+	*cmsp++ = '(';
+	memcpy(cmsp, info->lo_crypt_name, cipher_len);
+	cmsp += cipher_len;
+	*cmsp++ = ')';
+	*cmsp = 0;
+
+	tfm = crypto_alloc_skcipher(cms, 0, CRYPTO_ALG_ASYNC);
+	if (IS_ERR(tfm))
+		return PTR_ERR(tfm);
+
+	err = crypto_skcipher_setkey(tfm, info->lo_encrypt_key,
+				     info->lo_encrypt_key_size);
+	
+	if (err != 0)
+		goto out_free_tfm;
+
+	lo->key_data = tfm;
+	return 0;
+
+ out_free_tfm:
+	crypto_free_skcipher(tfm);
+
+ out:
+	return err;
+}
+
+
+typedef int (*encdec_cbc_t)(struct skcipher_request *req);
+
+static int
+cryptoloop_transfer(struct loop_device *lo, int cmd,
+		    struct page *raw_page, unsigned raw_off,
+		    struct page *loop_page, unsigned loop_off,
+		    int size, sector_t IV)
+{
+	struct crypto_skcipher *tfm = lo->key_data;
+	SKCIPHER_REQUEST_ON_STACK(req, tfm);
+	struct scatterlist sg_out;
+	struct scatterlist sg_in;
+
+	encdec_cbc_t encdecfunc;
+	struct page *in_page, *out_page;
+	unsigned in_offs, out_offs;
+	int err;
+
+	skcipher_request_set_tfm(req, tfm);
+	skcipher_request_set_callback(req, CRYPTO_TFM_REQ_MAY_SLEEP,
+				      NULL, NULL);
+
+	sg_init_table(&sg_out, 1);
+	sg_init_table(&sg_in, 1);
+
+	if (cmd == READ) {
+		in_page = raw_page;
+		in_offs = raw_off;
+		out_page = loop_page;
+		out_offs = loop_off;
+		encdecfunc = crypto_skcipher_decrypt;
+	} else {
+		in_page = loop_page;
+		in_offs = loop_off;
+		out_page = raw_page;
+		out_offs = raw_off;
+		encdecfunc = crypto_skcipher_encrypt;
+	}
+
+	while (size > 0) {
+		const int sz = min(size, LOOP_IV_SECTOR_SIZE);
+		u32 iv[4] = { 0, };
+		iv[0] = cpu_to_le32(IV & 0xffffffff);
+
+		sg_set_page(&sg_in, in_page, sz, in_offs);
+		sg_set_page(&sg_out, out_page, sz, out_offs);
+
+		skcipher_request_set_crypt(req, &sg_in, &sg_out, sz, iv);
+		err = encdecfunc(req);
+		if (err)
+			goto out;
+
+		IV++;
+		size -= sz;
+		in_offs += sz;
+		out_offs += sz;
+	}
+
+	err = 0;
+
+out:
+	skcipher_request_zero(req);
+	return err;
+}
+
+static int
+cryptoloop_ioctl(struct loop_device *lo, int cmd, unsigned long arg)
+{
+	return -EINVAL;
+}
+
+static int
+cryptoloop_release(struct loop_device *lo)
+{
+	struct crypto_skcipher *tfm = lo->key_data;
+	if (tfm != NULL) {
+		crypto_free_skcipher(tfm);
+		lo->key_data = NULL;
+		return 0;
+	}
+	printk(KERN_ERR "cryptoloop_release(): tfm == NULL?\n");
+	return -EINVAL;
+}
+
+static struct loop_func_table cryptoloop_funcs = {
+	.number = LO_CRYPT_CRYPTOAPI,
+	.init = cryptoloop_init,
+	.ioctl = cryptoloop_ioctl,
+	.transfer = cryptoloop_transfer,
+	.release = cryptoloop_release,
+	.owner = THIS_MODULE
+};
+
+static int __init
+init_cryptoloop(void)
+{
+	int rc = loop_register_transfer(&cryptoloop_funcs);
+
+	if (rc)
+		printk(KERN_ERR "cryptoloop: loop_register_transfer failed\n");
+	return rc;
+}
+
+static void __exit
+cleanup_cryptoloop(void)
+{
+	if (loop_unregister_transfer(LO_CRYPT_CRYPTOAPI))
+		printk(KERN_ERR
+			"cryptoloop: loop_unregister_transfer failed\n");
+}
+
+module_init(init_cryptoloop);
+module_exit(cleanup_cryptoloop);
diff --git a/loop_file_fmt.c b/loop_file_fmt.c
new file mode 100644
index 0000000..ff356f1
--- /dev/null
+++ b/loop_file_fmt.c
@@ -0,0 +1,328 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * loop_file_fmt.c
+ *
+ * File format subsystem for the loop device module.
+ *
+ * Copyright (C) 2019 Manuel Bentele <development@manuel-bentele.de>
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+
+#include "loop_file_fmt.h"
+
+/* storage for all registered file format drivers */
+static struct loop_file_fmt_driver *loop_file_fmt_drivers[MAX_LO_FILE_FMT] = {
+	NULL
+};
+
+int loop_file_fmt_register_driver(struct loop_file_fmt_driver *drv)
+{
+	int ret = 0;
+
+	if (drv == NULL)
+		return -EFAULT;
+
+	if (drv->file_fmt_type > MAX_LO_FILE_FMT)
+		return -EINVAL;
+
+	if (loop_file_fmt_drivers[drv->file_fmt_type] == NULL) {
+		loop_file_fmt_drivers[drv->file_fmt_type] = drv;
+		printk(KERN_INFO "loop_file_fmt: successfully registered file "
+			"format driver %s", drv->name);
+	} else {
+		printk(KERN_WARNING "loop_file_fmt: driver for file format "
+			"already registered");
+		ret = -EBUSY;
+	}
+
+	return ret;
+}
+EXPORT_SYMBOL(loop_file_fmt_register_driver);
+
+void loop_file_fmt_unregister_driver(struct loop_file_fmt_driver *drv)
+{
+	if (drv == NULL)
+		return;
+
+	if (drv->file_fmt_type > MAX_LO_FILE_FMT)
+		return;
+
+	loop_file_fmt_drivers[drv->file_fmt_type] = NULL;
+	printk(KERN_INFO "loop_file_fmt: successfully unregistered file "
+		"format driver %s", drv->name);
+}
+EXPORT_SYMBOL(loop_file_fmt_unregister_driver);
+
+struct loop_file_fmt *loop_file_fmt_alloc(void)
+{
+	return kzalloc(sizeof(struct loop_file_fmt), GFP_KERNEL);
+}
+
+void loop_file_fmt_free(struct loop_file_fmt *lo_fmt)
+{
+	kfree(lo_fmt);
+}
+
+int loop_file_fmt_set_lo(struct loop_file_fmt *lo_fmt, struct loop_device *lo)
+{
+	if (lo_fmt == NULL)
+		return -EINVAL;
+
+	lo_fmt->lo = lo;
+
+	return 0;
+}
+EXPORT_SYMBOL(loop_file_fmt_set_lo);
+
+struct loop_device *loop_file_fmt_get_lo(struct loop_file_fmt *lo_fmt)
+{
+	return lo_fmt->lo;
+}
+EXPORT_SYMBOL(loop_file_fmt_get_lo);
+
+int loop_file_fmt_init(struct loop_file_fmt *lo_fmt,
+		       u32 file_fmt_type)
+{
+	struct loop_file_fmt_ops *ops;
+	struct module *drv;
+	int ret = 0;
+
+	if (file_fmt_type > MAX_LO_FILE_FMT)
+		return -EINVAL;
+
+	lo_fmt->file_fmt_type = file_fmt_type;
+
+	if (lo_fmt->file_fmt_state != file_fmt_uninitialized) {
+		printk(KERN_WARNING "loop_file_fmt: file format is "
+			"initialized already");
+		return -EINVAL;
+	}
+
+	/* check if new file format driver is registered */
+	if (loop_file_fmt_drivers[lo_fmt->file_fmt_type] == NULL) {
+		printk(KERN_ERR "loop_file_fmt: file format driver is not "
+			"available");
+		return -ENODEV;
+	}
+
+	printk(KERN_INFO "loop_file_fmt: use file format driver %s",
+		loop_file_fmt_drivers[lo_fmt->file_fmt_type]->name);
+
+	drv = loop_file_fmt_drivers[lo_fmt->file_fmt_type]->owner;
+	if (!try_module_get(drv)) {
+		printk(KERN_ERR "loop_file_fmt: file format driver %s can not "
+			"be accessed",
+			loop_file_fmt_drivers[lo_fmt->file_fmt_type]->name);
+		return -ENODEV;
+	}
+
+	ops = loop_file_fmt_drivers[lo_fmt->file_fmt_type]->ops;
+	if (likely(ops->init)) {
+		ret = ops->init(lo_fmt);
+		if (ret < 0)
+			goto free_drv;
+	}
+
+	/* after increasing the refcount of file format driver module and
+	 * the successful initialization, the file format is initialized */
+	lo_fmt->file_fmt_state = file_fmt_initialized;
+
+	return ret;
+
+free_drv:
+	module_put(drv);
+	lo_fmt->file_fmt_state = file_fmt_uninitialized;
+	return ret;
+}
+
+void loop_file_fmt_exit(struct loop_file_fmt *lo_fmt)
+{
+	struct loop_file_fmt_ops *ops;
+	struct module *drv;
+
+	if (lo_fmt->file_fmt_state != file_fmt_initialized) {
+		printk(KERN_WARNING "loop_file_fmt: file format is "
+			"uninitialized already");
+		return;
+	}
+
+	ops = loop_file_fmt_drivers[lo_fmt->file_fmt_type]->ops;
+	if (likely(ops->exit))
+		ops->exit(lo_fmt);
+
+	drv = loop_file_fmt_drivers[lo_fmt->file_fmt_type]->owner;
+	module_put(drv);
+
+	/* after decreasing the refcount of file format driver module,
+	 * the file format is uninitialized */
+	lo_fmt->file_fmt_state = file_fmt_uninitialized;
+}
+
+int loop_file_fmt_read(struct loop_file_fmt *lo_fmt,
+		       struct request *rq)
+{
+	struct loop_file_fmt_ops *ops;
+
+	if (unlikely(lo_fmt->file_fmt_state != file_fmt_initialized)) {
+		printk(KERN_ERR "loop_file_fmt: file format is "
+			"not initialized, can not read");
+		return -EINVAL;
+	}
+
+	ops = loop_file_fmt_drivers[lo_fmt->file_fmt_type]->ops;
+	if (likely(ops->read))
+		return ops->read(lo_fmt, rq);
+	else
+		return -EIO;
+}
+
+int loop_file_fmt_read_aio(struct loop_file_fmt *lo_fmt,
+			   struct request *rq)
+{
+	struct loop_file_fmt_ops *ops;
+
+	if (unlikely(lo_fmt->file_fmt_state != file_fmt_initialized)) {
+		printk(KERN_ERR "loop_file_fmt: file format is "
+				"not initialized, can not read aio");
+		return -EINVAL;
+	}
+
+	ops = loop_file_fmt_drivers[lo_fmt->file_fmt_type]->ops;
+	if (likely(ops->read_aio))
+		return ops->read_aio(lo_fmt, rq);
+	else
+		return -EIO;
+}
+
+int loop_file_fmt_write(struct loop_file_fmt *lo_fmt,
+			struct request *rq)
+{
+	struct loop_file_fmt_ops *ops;
+
+	if (unlikely(lo_fmt->file_fmt_state != file_fmt_initialized)) {
+		printk(KERN_ERR "loop_file_fmt: file format is "
+				"not initialized, can not write");
+		return -EINVAL;
+	}
+
+	ops = loop_file_fmt_drivers[lo_fmt->file_fmt_type]->ops;
+	if (likely(ops->write))
+		return ops->write(lo_fmt, rq);
+	else
+		return -EIO;
+}
+
+int loop_file_fmt_write_aio(struct loop_file_fmt *lo_fmt,
+			    struct request *rq)
+{
+	struct loop_file_fmt_ops *ops;
+
+	if (unlikely(lo_fmt->file_fmt_state != file_fmt_initialized)) {
+		printk(KERN_ERR "loop_file_fmt: file format is "
+				"not initialized, can not write aio");
+		return -EINVAL;
+	}
+
+	ops = loop_file_fmt_drivers[lo_fmt->file_fmt_type]->ops;
+	if (likely(ops->write_aio))
+		return ops->write_aio(lo_fmt, rq);
+	else
+		return -EIO;
+}
+
+int loop_file_fmt_discard(struct loop_file_fmt *lo_fmt,
+			  struct request *rq)
+{
+	struct loop_file_fmt_ops *ops;
+
+	if (unlikely(lo_fmt->file_fmt_state != file_fmt_initialized)) {
+		printk(KERN_ERR "loop_file_fmt: file format is "
+				"not initialized, can not discard");
+		return -EINVAL;
+	}
+
+	ops = loop_file_fmt_drivers[lo_fmt->file_fmt_type]->ops;
+	if (likely(ops->discard))
+		return ops->discard(lo_fmt, rq);
+	else
+		return -EIO;
+}
+
+int loop_file_fmt_flush(struct loop_file_fmt *lo_fmt)
+{
+	struct loop_file_fmt_ops *ops;
+
+	if (unlikely(lo_fmt->file_fmt_state != file_fmt_initialized)) {
+		printk(KERN_ERR "loop_file_fmt: file format is "
+				"not initialized, can not flush");
+		return -EINVAL;
+	}
+
+	ops = loop_file_fmt_drivers[lo_fmt->file_fmt_type]->ops;
+	if (likely(ops->flush))
+		return ops->flush(lo_fmt);
+
+	return 0;
+}
+
+loff_t loop_file_fmt_sector_size(struct loop_file_fmt *lo_fmt)
+{
+	struct loop_file_fmt_ops *ops;
+
+	if (unlikely(lo_fmt->file_fmt_state != file_fmt_initialized)) {
+		printk(KERN_ERR "loop_file_fmt: file format is "
+				"not initialized, can not read sector size");
+		return 0;
+	}
+
+	ops = loop_file_fmt_drivers[lo_fmt->file_fmt_type]->ops;
+	if (likely(ops->sector_size))
+		return ops->sector_size(lo_fmt);
+	else
+		return 0;
+}
+
+int loop_file_fmt_change(struct loop_file_fmt *lo_fmt,
+			 u32 file_fmt_type_new)
+{
+	if (file_fmt_type_new > MAX_LO_FILE_FMT)
+		return -EINVAL;
+
+	/* Unload the old file format driver if the file format is
+	 * initialized */
+	if (lo_fmt->file_fmt_state == file_fmt_initialized)
+		loop_file_fmt_exit(lo_fmt);
+
+	/* Load the new file format driver because the file format is
+	 * uninitialized now */
+	return loop_file_fmt_init(lo_fmt, file_fmt_type_new);
+}
+
+ssize_t loop_file_fmt_print_type(u32 file_fmt_type, char *file_fmt_name)
+{
+	ssize_t len = 0;
+
+	switch (file_fmt_type) {
+	case LO_FILE_FMT_RAW:
+		len = sprintf(file_fmt_name, "%s", "RAW");
+		break;
+	case LO_FILE_FMT_QCOW:
+		len = sprintf(file_fmt_name, "%s", "QCOW");
+		break;
+	case LO_FILE_FMT_VDI:
+		len = sprintf(file_fmt_name, "%s", "VDI");
+		break;
+	case LO_FILE_FMT_VMDK:
+		len = sprintf(file_fmt_name, "%s", "VMDK");
+		break;
+	default:
+		len = sprintf(file_fmt_name, "%s", "ERROR: Unsupported loop "
+			"file format!");
+		break;
+	}
+
+	return len;
+}
+EXPORT_SYMBOL(loop_file_fmt_print_type);
diff --git a/loop_file_fmt.h b/loop_file_fmt.h
new file mode 100644
index 0000000..5c0e493
--- /dev/null
+++ b/loop_file_fmt.h
@@ -0,0 +1,351 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * loop_file_fmt.h
+ *
+ * File format subsystem for the loop device module.
+ *
+ * Copyright (C) 2019 Manuel Bentele <development@manuel-bentele.de>
+ */
+
+#ifndef _LINUX_LOOP_FILE_FMT_H
+#define _LINUX_LOOP_FILE_FMT_H
+
+#include "loop_main.h"
+
+struct loop_file_fmt;
+
+/**
+ * struct loop_file_fmt_ops - File format subsystem operations
+ *
+ * Data structure representing the file format subsystem interface.
+ */
+struct loop_file_fmt_ops {
+	/**
+	 * @init: Initialization callback function
+	 */
+	int (*init) (struct loop_file_fmt *lo_fmt);
+
+	/**
+	 * @exit: Release callback function
+	 */
+	void (*exit) (struct loop_file_fmt *lo_fmt);
+
+	/**
+	 * @read: Read IO callback function
+	 */
+	int (*read) (struct loop_file_fmt *lo_fmt,
+		     struct request *rq);
+
+	/**
+	 * @write: Write IO callback function
+	 */
+	int (*write) (struct loop_file_fmt *lo_fmt,
+		      struct request *rq);
+
+	/**
+	 * @read_aio: Asynchronous read IO callback function
+	 */
+	int (*read_aio) (struct loop_file_fmt *lo_fmt,
+			 struct request *rq);
+
+	/**
+	 * @write_aio: Asynchronous write IO callback function
+	 */
+	int (*write_aio) (struct loop_file_fmt *lo_fmt,
+			  struct request *rq);
+
+	/**
+	 * @discard: Discard IO callback function
+	 */
+	int (*discard) (struct loop_file_fmt *lo_fmt,
+			struct request *rq);
+
+	/**
+	 * @flush: Flush callback function
+	 */
+	int (*flush) (struct loop_file_fmt *lo_fmt);
+
+	/**
+	 * @sector_size: Get sector size callback function
+	 */
+	loff_t (*sector_size) (struct loop_file_fmt *lo_fmt);
+};
+
+/**
+ * struct loop_file_fmt_driver - File format subsystem driver
+ *
+ * Data structure to implement file format drivers for the file format
+ * subsystem.
+ */
+struct loop_file_fmt_driver {
+	/**
+	 * @name: Name of the file format driver
+	 */
+	const char *name;
+
+	/**
+	 * @file_fmt_type: Loop file format type of the file format driver
+	 */
+	const u32 file_fmt_type;
+
+	/**
+	 * @ops: Driver's implemented file format operations
+	 */
+	struct loop_file_fmt_ops *ops;
+
+	/**
+	 * @ops: Owner of the file format driver
+	 */
+	struct module *owner;
+};
+
+/*
+ * states of the file format
+ *
+ * transitions:
+ *                    loop_file_fmt_init(...)
+ * ---> uninitialized ------------------------------> initialized
+ *                    loop_file_fmt_exit(...)
+ *      initialized   ------------------------------> uninitialized
+ *                    loop_file_fmt_read(...)
+ *      initialized   ------------------------------> initialized
+ *                    loop_file_fmt_read_aio(...)
+ *      initialized   ------------------------------> initialized
+ *                    loop_file_fmt_write(...)
+ *      initialized   ------------------------------> initialized
+ *                    loop_file_fmt_write_aio(...)
+ *      initialized   ------------------------------> initialized
+ *                    loop_file_fmt_discard(...)
+ *      initialized   ------------------------------> initialized
+ *                    loop_file_fmt_flush(...)
+ *      initialized   ------------------------------> initialized
+ *                    loop_file_fmt_sector_size(...)
+ *      initialized   ------------------------------> initialized
+ *
+ *                    loop_file_fmt_change(...)
+ *    +-----------------------------------------------------------+
+ *    |               exit(...)              init(...)            |
+ *    | initialized   -------> uninitialized -------> initialized |
+ *    +-----------------------------------------------------------+
+ */
+enum {
+	file_fmt_uninitialized = 0,
+	file_fmt_initialized
+};
+
+/**
+ * struct loop_file_fmt - Loop file format
+ *
+ * Data structure to use with the file format the loop file format subsystem.
+ */
+struct loop_file_fmt {
+	/**
+	 * @file_fmt_type: Current type of the loop file format
+	 */
+	u32 file_fmt_type;
+
+	/**
+	 * @file_fmt_state: Current state of the loop file format
+	 */
+	int file_fmt_state;
+
+	/**
+	 * @lo: Link to a file format's loop device
+	 */
+	struct loop_device *lo;
+
+	/**
+	 * @private_data: Optional link to a file format's driver specific data
+	 */
+	void *private_data;
+};
+
+
+/* subsystem functions for the driver implementation */
+
+/**
+ * loop_file_fmt_register_driver - Register a loop file format driver
+ * @drv: File format driver
+ *
+ * Registers the specified loop file format driver @drv by the loop file format
+ * subsystem.
+ */
+extern int loop_file_fmt_register_driver(struct loop_file_fmt_driver *drv);
+
+/**
+ * loop_file_fmt_unregister_driver - Unregister a loop file format driver
+ * @drv: File format driver
+ *
+ * Unregisters the specified loop file format driver @drv from the loop file
+ * format subsystem.
+ */
+extern void loop_file_fmt_unregister_driver(struct loop_file_fmt_driver *drv);
+
+
+/* subsystem functions for subsystem usage */
+
+/**
+ * loop_file_fmt_alloc - Allocate a loop file format
+ *
+ * Dynamically allocates a loop file format and returns a pointer to the
+ * created loop file format.
+ */
+extern struct loop_file_fmt *loop_file_fmt_alloc(void);
+
+/**
+ * loop_file_fmt_free - Free an allocated loop file format
+ * @lo_fmt: Loop file format
+ *
+ * Frees the already allocated loop file format @lo_fmt.
+ */
+extern void loop_file_fmt_free(struct loop_file_fmt *lo_fmt);
+
+/**
+ * loop_file_fmt_set_lo - Set the loop file format's loop device
+ * @lo_fmt: Loop file format
+ * @lo: Loop device
+ *
+ * The link to the loop device @lo is set in the loop file format @lo_fmt.
+ */
+extern int loop_file_fmt_set_lo(struct loop_file_fmt *lo_fmt,
+				struct loop_device *lo);
+
+/**
+ * loop_file_fmt_get_lo - Get the loop file format's loop device
+ * @lo_fmt: Loop file format
+ *
+ * Returns a pointer to the loop device of the loop file format @lo_fmt.
+ */
+extern struct loop_device *loop_file_fmt_get_lo(struct loop_file_fmt *lo_fmt);
+
+/**
+ * loop_file_fmt_init - Initialize a loop file format
+ * @lo_fmt: Loop file format
+ * @file_fmt_type: Type of the file format
+ *
+ * Initializes the specified loop file format @lo_fmt and sets up the correct
+ * file format type @file_fmt_type. Depending on @file_fmt_type, the correct
+ * loop file format driver is loaded in the subsystems backend. If no loop file
+ * format driver for the specified file format is available an error is
+ * returned.
+ */
+extern int loop_file_fmt_init(struct loop_file_fmt *lo_fmt,
+			      u32 file_fmt_type);
+
+/**
+ * loop_file_fmt_exit - Release a loop file format
+ * @lo_fmt: Loop file format
+ *
+ * Releases the specified loop file format @lo_fmt and all its resources.
+ */
+extern void loop_file_fmt_exit(struct loop_file_fmt *lo_fmt);
+
+/**
+ * loop_file_fmt_read - Read IO from a loop file format
+ * @lo_fmt: Loop file format
+ * @rq: IO Request
+ *
+ * Reads IO from the file format's loop device by sending the IO read request
+ * @rq to the loop file format subsystem. The subsystem calls the registered
+ * callback function of the suitable loop file format driver.
+ */
+extern int loop_file_fmt_read(struct loop_file_fmt *lo_fmt,
+			      struct request *rq);
+
+/**
+ * loop_file_fmt_read_aio - Read IO from a loop file format asynchronously
+ * @lo_fmt: Loop file format
+ * @rq: IO Request
+ *
+ * Reads IO from the file format's loop device asynchronously by sending the
+ * IO read aio request @rq to the loop file format subsystem. The subsystem
+ * calls the registered callback function of the suitable loop file format
+ * driver.
+ */
+extern int loop_file_fmt_read_aio(struct loop_file_fmt *lo_fmt,
+				  struct request *rq);
+
+/**
+ * loop_file_fmt_write - Write IO to a loop file format
+ * @lo_fmt: Loop file format
+ * @rq: IO Request
+ *
+ * Write IO to the file format's loop device by sending the IO write request
+ * @rq to the loop file format subsystem. The subsystem calls the registered
+ * callback function of the suitable loop file format driver.
+ */
+extern int loop_file_fmt_write(struct loop_file_fmt *lo_fmt,
+			       struct request *rq);
+
+/**
+ * loop_file_fmt_write_aio - Write IO to a loop file format asynchronously
+ * @lo_fmt: Loop file format
+ * @rq: IO Request
+ *
+ * Write IO to the file format's loop device asynchronously by sending the
+ * IO write aio request @rq to the loop file format subsystem. The subsystem
+ * calls the registered callback function of the suitable loop file format
+ * driver.
+ */
+extern int loop_file_fmt_write_aio(struct loop_file_fmt *lo_fmt,
+				   struct request *rq);
+
+/**
+ * loop_file_fmt_discard - Discard IO on a loop file format
+ * @lo_fmt: Loop file format
+ * @rq: IO Request
+ *
+ * Discard IO on the file format's loop device by sending the IO discard
+ * request @rq to the loop file format subsystem. The subsystem calls the
+ * registered callback function of the suitable loop file format driver.
+ */
+extern int loop_file_fmt_discard(struct loop_file_fmt *lo_fmt,
+				 struct request *rq);
+
+/**
+ * loop_file_fmt_flush - Flush a loop file format
+ * @lo_fmt: Loop file format
+ *
+ * Flush the file format's loop device by calling the registered callback
+ * function of the suitable loop file format driver.
+ */
+extern int loop_file_fmt_flush(struct loop_file_fmt *lo_fmt);
+
+/**
+ * loop_file_fmt_sector_size - Get sector size of a loop file format
+ * @lo_fmt: Loop file format
+ *
+ * Returns the physical sector size of the loop file format's loop device.
+ * If the loop file format implements a sparse disk image format, then this
+ * function returns the virtual sector size.
+ */
+extern loff_t loop_file_fmt_sector_size(struct loop_file_fmt *lo_fmt);
+
+/**
+ * loop_file_fmt_change - Change the loop file format's type
+ * @lo_fmt: Loop file format
+ * @file_fmt_type_new: Loop file format type
+ *
+ * Changes the file format type of the already initialized loop file format
+ * @lo_fmt. Therefore, the function releases the old file format and frees all
+ * of its resources before the loop file format @lo_fmt is initialized and set
+ * up with the new file format @file_fmt_type_new.
+ */
+extern int loop_file_fmt_change(struct loop_file_fmt *lo_fmt,
+				u32 file_fmt_type_new);
+
+
+/* helper functions of the subsystem */
+
+/**
+ * loop_file_fmt_print_type - Convert file format type to string
+ * @file_fmt_type: Loop file format type
+ * @file_fmt_name: Loop file format type string
+ *
+ * Converts the specified numeric @file_fmt_type value into a human readable
+ * string stating the file format as string in @file_fmt_name.
+ */
+extern ssize_t loop_file_fmt_print_type(u32 file_fmt_type,
+					char *file_fmt_name);
+
+#endif
diff --git a/loop_file_fmt_qcow_cache.c b/loop_file_fmt_qcow_cache.c
new file mode 100644
index 0000000..7d3af73
--- /dev/null
+++ b/loop_file_fmt_qcow_cache.c
@@ -0,0 +1,218 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * loop_file_fmt_qcow_cache.c
+ *
+ * QCOW file format driver for the loop device module.
+ *
+ * Ported QCOW2 implementation of the QEMU project (GPL-2.0):
+ * L2/refcount table cache for the QCOW2 format.
+ *
+ * The copyright (C) 2010 of the original code is owned by
+ * Kevin Wolf <kwolf@redhat.com>
+ *
+ * Copyright (C) 2019 Manuel Bentele <development@manuel-bentele.de>
+ */
+
+#include <linux/kernel.h>
+#include <linux/log2.h>
+#include <linux/types.h>
+#include <linux/limits.h>
+#include <linux/fs.h>
+#include <linux/vmalloc.h>
+
+#include "loop_file_fmt_qcow_main.h"
+#include "loop_file_fmt_qcow_cache.h"
+
+static inline void *__loop_file_fmt_qcow_cache_get_table_addr(
+	struct loop_file_fmt_qcow_cache *c, int table)
+{
+	return (u8 *) c->table_array + (size_t) table * c->table_size;
+}
+
+static inline int __loop_file_fmt_qcow_cache_get_table_idx(
+	struct loop_file_fmt_qcow_cache *c, void *table)
+{
+	ptrdiff_t table_offset = (u8 *) table - (u8 *) c->table_array;
+	int idx = table_offset / c->table_size;
+	ASSERT(idx >= 0 && idx < c->size && table_offset % c->table_size == 0);
+	return idx;
+}
+
+static inline const char *__loop_file_fmt_qcow_cache_get_name(
+	struct loop_file_fmt *lo_fmt, struct loop_file_fmt_qcow_cache *c)
+{
+	struct loop_file_fmt_qcow_data *qcow_data = lo_fmt->private_data;
+
+	if (c == qcow_data->refcount_block_cache) {
+		return "refcount block";
+	} else if (c == qcow_data->l2_table_cache) {
+		return "L2 table";
+	} else {
+		/* do not abort, because this is not critical */
+		return "unknown";
+	}
+}
+
+struct loop_file_fmt_qcow_cache *loop_file_fmt_qcow_cache_create(
+	struct loop_file_fmt *lo_fmt, int num_tables, unsigned table_size)
+{
+#ifdef CONFIG_DEBUG_DRIVER
+	struct loop_file_fmt_qcow_data *qcow_data = lo_fmt->private_data;
+#endif
+	struct loop_file_fmt_qcow_cache *c;
+
+	ASSERT(num_tables > 0);
+	ASSERT(is_power_of_2(table_size));
+	ASSERT(table_size >= (1 << QCOW_MIN_CLUSTER_BITS));
+	ASSERT(table_size <= qcow_data->cluster_size);
+
+	c = kzalloc(sizeof(*c), GFP_KERNEL);
+	if (!c) {
+		return NULL;
+	}
+
+	c->size = num_tables;
+	c->table_size = table_size;
+	c->entries = vzalloc(sizeof(struct loop_file_fmt_qcow_cache_table) *
+		num_tables);
+	c->table_array = vzalloc(num_tables * c->table_size);
+
+	if (!c->entries || !c->table_array) {
+		vfree(c->table_array);
+		vfree(c->entries);
+		kfree(c);
+		c = NULL;
+	}
+
+	return c;
+}
+
+void loop_file_fmt_qcow_cache_destroy(struct loop_file_fmt *lo_fmt)
+{
+	struct loop_file_fmt_qcow_data *qcow_data = lo_fmt->private_data;
+	struct loop_file_fmt_qcow_cache *c = qcow_data->l2_table_cache;
+	int i;
+
+	for (i = 0; i < c->size; i++) {
+		ASSERT(c->entries[i].ref == 0);
+	}
+
+	vfree(c->table_array);
+	vfree(c->entries);
+	kfree(c);
+}
+
+static int __loop_file_fmt_qcow_cache_entry_flush(
+	struct loop_file_fmt_qcow_cache *c, int i)
+{
+	if (!c->entries[i].dirty || !c->entries[i].offset) {
+		return 0;
+	} else {
+		printk(KERN_ERR "loop_file_fmt_qcow: Flush dirty cache tables "
+			"is not supported yet\n");
+		return -ENOSYS;
+	}
+}
+
+static int __loop_file_fmt_qcow_cache_do_get(struct loop_file_fmt *lo_fmt,
+	struct loop_file_fmt_qcow_cache *c, u64 offset, void **table,
+	bool read_from_disk)
+{
+	struct loop_device *lo = loop_file_fmt_get_lo(lo_fmt);
+	int i;
+	int ret;
+	int lookup_index;
+	u64 min_lru_counter = U64_MAX;
+	int min_lru_index = -1;
+	u64 read_offset;
+	size_t len;
+
+	ASSERT(offset != 0);
+
+	if (!IS_ALIGNED(offset, c->table_size)) {
+		printk_ratelimited(KERN_ERR "loop_file_fmt_qcow: Cannot get "
+			"entry from %s cache: offset %llx is unaligned\n",
+			__loop_file_fmt_qcow_cache_get_name(lo_fmt, c),
+			offset);
+		return -EIO;
+	}
+
+	/* Check if the table is already cached */
+	i = lookup_index = (offset / c->table_size * 4) % c->size;
+	do {
+		const struct loop_file_fmt_qcow_cache_table *t =
+			&c->entries[i];
+		if (t->offset == offset) {
+			goto found;
+		}
+		if (t->ref == 0 && t->lru_counter < min_lru_counter) {
+			min_lru_counter = t->lru_counter;
+			min_lru_index = i;
+		}
+		if (++i == c->size) {
+			i = 0;
+		}
+	} while (i != lookup_index);
+
+	if (min_lru_index == -1) {
+		BUG();
+		panic("Oops: This can't happen in current synchronous code, "
+			"but leave the check here as a reminder for whoever "
+			"starts using AIO with the QCOW cache");
+	}
+
+	/* Cache miss: write a table back and replace it */
+	i = min_lru_index;
+
+	ret = __loop_file_fmt_qcow_cache_entry_flush(c, i);
+	if (ret < 0) {
+		return ret;
+	}
+
+	c->entries[i].offset = 0;
+	if (read_from_disk) {
+		read_offset = offset;
+		len = kernel_read(lo->lo_backing_file,
+			__loop_file_fmt_qcow_cache_get_table_addr(c, i),
+			c->table_size, &read_offset);
+		if (len < 0) {
+			len = ret;
+			return ret;
+		}
+	}
+
+	c->entries[i].offset = offset;
+
+	/* And return the right table */
+found:
+	c->entries[i].ref++;
+	*table = __loop_file_fmt_qcow_cache_get_table_addr(c, i);
+
+	return 0;
+}
+
+int loop_file_fmt_qcow_cache_get(struct loop_file_fmt *lo_fmt, u64 offset,
+	void **table)
+{
+	struct loop_file_fmt_qcow_data *qcow_data = lo_fmt->private_data;
+	struct loop_file_fmt_qcow_cache *c = qcow_data->l2_table_cache;
+
+	return __loop_file_fmt_qcow_cache_do_get(lo_fmt, c, offset, table,
+		true);
+}
+
+void loop_file_fmt_qcow_cache_put(struct loop_file_fmt *lo_fmt, void **table)
+{
+	struct loop_file_fmt_qcow_data *qcow_data = lo_fmt->private_data;
+	struct loop_file_fmt_qcow_cache *c = qcow_data->l2_table_cache;
+	int i = __loop_file_fmt_qcow_cache_get_table_idx(c, *table);
+
+	c->entries[i].ref--;
+	*table = NULL;
+
+	if (c->entries[i].ref == 0) {
+		c->entries[i].lru_counter = ++c->lru_counter;
+	}
+
+	ASSERT(c->entries[i].ref >= 0);
+}
diff --git a/loop_file_fmt_qcow_cache.h b/loop_file_fmt_qcow_cache.h
new file mode 100644
index 0000000..1abf9b2
--- /dev/null
+++ b/loop_file_fmt_qcow_cache.h
@@ -0,0 +1,51 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * loop_file_fmt_qcow_cache.h
+ *
+ * Ported QCOW2 implementation of the QEMU project (GPL-2.0):
+ * L2/refcount table cache for the QCOW2 format.
+ *
+ * The copyright (C) 2010 of the original code is owned by
+ * Kevin Wolf <kwolf@redhat.com>
+ *
+ * Copyright (C) 2019 Manuel Bentele <development@manuel-bentele.de>
+ */
+
+#ifndef _LINUX_LOOP_FILE_FMT_QCOW_CACHE_H
+#define _LINUX_LOOP_FILE_FMT_QCOW_CACHE_H
+
+#include "loop_file_fmt.h"
+
+struct loop_file_fmt_qcow_cache_table {
+	s64 offset;
+	u64 lru_counter;
+	int ref;
+	bool dirty;
+};
+
+struct loop_file_fmt_qcow_cache {
+	struct loop_file_fmt_qcow_cache_table *entries;
+	struct loop_file_fmt_qcow_cache *depends;
+	int size;
+	int table_size;
+	bool depends_on_flush;
+	void *table_array;
+	u64 lru_counter;
+	u64 cache_clean_lru_counter;
+};
+
+extern struct loop_file_fmt_qcow_cache *loop_file_fmt_qcow_cache_create(
+	struct loop_file_fmt *lo_fmt,
+	int num_tables,
+	unsigned table_size);
+
+extern void loop_file_fmt_qcow_cache_destroy(struct loop_file_fmt *lo_fmt);
+
+extern int loop_file_fmt_qcow_cache_get(struct loop_file_fmt *lo_fmt,
+					u64 offset,
+					void **table);
+
+extern void loop_file_fmt_qcow_cache_put(struct loop_file_fmt *lo_fmt,
+					 void **table);
+
+#endif
diff --git a/loop_file_fmt_qcow_cluster.c b/loop_file_fmt_qcow_cluster.c
new file mode 100644
index 0000000..9c91a8b
--- /dev/null
+++ b/loop_file_fmt_qcow_cluster.c
@@ -0,0 +1,270 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * loop_file_fmt_qcow_cluster.c
+ *
+ * Ported QCOW2 implementation of the QEMU project (GPL-2.0):
+ * Cluster calculation and lookup for the QCOW2 format.
+ *
+ * The copyright (C) 2004-2006 of the original code is owned by Fabrice Bellard.
+ *
+ * Copyright (C) 2019 Manuel Bentele <development@manuel-bentele.de>
+ */
+
+#include <linux/kernel.h>
+#include <linux/string.h>
+
+#include "loop_file_fmt.h"
+#include "loop_file_fmt_qcow_main.h"
+#include "loop_file_fmt_qcow_cache.h"
+#include "loop_file_fmt_qcow_cluster.h"
+
+/*
+ * Loads a L2 slice into memory (L2 slices are the parts of L2 tables
+ * that are loaded by the qcow2 cache). If the slice is in the cache,
+ * the cache is used; otherwise the L2 slice is loaded from the image
+ * file.
+ */
+static int __loop_file_fmt_qcow_cluster_l2_load(struct loop_file_fmt *lo_fmt,
+	u64 offset, u64 l2_offset, u64 **l2_slice)
+{
+	struct loop_file_fmt_qcow_data *qcow_data = lo_fmt->private_data;
+
+	int start_of_slice = sizeof(u64) * (
+		loop_file_fmt_qcow_offset_to_l2_index(qcow_data, offset) -
+		loop_file_fmt_qcow_offset_to_l2_slice_index(qcow_data, offset)
+	);
+
+	ASSERT(qcow_data->l2_table_cache != NULL);
+	return loop_file_fmt_qcow_cache_get(lo_fmt, l2_offset + start_of_slice,
+		(void **) l2_slice);
+}
+
+/*
+ * Checks how many clusters in a given L2 slice are contiguous in the image
+ * file. As soon as one of the flags in the bitmask stop_flags changes compared
+ * to the first cluster, the search is stopped and the cluster is not counted
+ * as contiguous. (This allows it, for example, to stop at the first compressed
+ * cluster which may require a different handling)
+ */
+static int __loop_file_fmt_qcow_cluster_count_contiguous(
+	struct loop_file_fmt *lo_fmt, int nb_clusters, int cluster_size,
+	u64 *l2_slice, u64 stop_flags)
+{
+	int i;
+	enum loop_file_fmt_qcow_cluster_type first_cluster_type;
+	u64 mask = stop_flags | L2E_OFFSET_MASK | QCOW_OFLAG_COMPRESSED;
+	u64 first_entry = be64_to_cpu(l2_slice[0]);
+	u64 offset = first_entry & mask;
+
+	first_cluster_type = loop_file_fmt_qcow_get_cluster_type(lo_fmt,
+		first_entry);
+	if (first_cluster_type == QCOW_CLUSTER_UNALLOCATED) {
+		return 0;
+	}
+
+	/* must be allocated */
+	ASSERT(first_cluster_type == QCOW_CLUSTER_NORMAL ||
+		first_cluster_type == QCOW_CLUSTER_ZERO_ALLOC);
+
+	for (i = 0; i < nb_clusters; i++) {
+		u64 l2_entry = be64_to_cpu(l2_slice[i]) & mask;
+		if (offset + (u64) i * cluster_size != l2_entry) {
+			break;
+		}
+	}
+
+	return i;
+}
+
+/*
+ * Checks how many consecutive unallocated clusters in a given L2
+ * slice have the same cluster type.
+ */
+static int __loop_file_fmt_qcow_cluster_count_contiguous_unallocated(
+	struct loop_file_fmt *lo_fmt, int nb_clusters, u64 *l2_slice,
+	enum loop_file_fmt_qcow_cluster_type wanted_type)
+{
+	int i;
+
+	ASSERT(wanted_type == QCOW_CLUSTER_ZERO_PLAIN ||
+		wanted_type == QCOW_CLUSTER_UNALLOCATED);
+
+	for (i = 0; i < nb_clusters; i++) {
+		u64 entry = be64_to_cpu(l2_slice[i]);
+		enum loop_file_fmt_qcow_cluster_type type =
+			loop_file_fmt_qcow_get_cluster_type(lo_fmt, entry);
+
+		if (type != wanted_type) {
+			break;
+		}
+	}
+
+	return i;
+}
+
+/*
+ * For a given offset of the virtual disk, find the cluster type and offset in
+ * the qcow2 file. The offset is stored in *cluster_offset.
+ *
+ * On entry, *bytes is the maximum number of contiguous bytes starting at
+ * offset that we are interested in.
+ *
+ * On exit, *bytes is the number of bytes starting at offset that have the same
+ * cluster type and (if applicable) are stored contiguously in the image file.
+ * Compressed clusters are always returned one by one.
+ *
+ * Returns the cluster type (QCOW2_CLUSTER_*) on success, -errno in error
+ * cases.
+ */
+int loop_file_fmt_qcow_cluster_get_offset(struct loop_file_fmt *lo_fmt,
+	u64 offset, unsigned int *bytes, u64 *cluster_offset)
+{
+	struct loop_file_fmt_qcow_data *qcow_data = lo_fmt->private_data;
+	unsigned int l2_index;
+	u64 l1_index, l2_offset, *l2_slice;
+	int c;
+	unsigned int offset_in_cluster;
+	u64 bytes_available, bytes_needed, nb_clusters;
+	enum loop_file_fmt_qcow_cluster_type type;
+	int ret;
+
+	offset_in_cluster = loop_file_fmt_qcow_offset_into_cluster(qcow_data,
+		offset);
+	bytes_needed = (u64) *bytes + offset_in_cluster;
+
+	/* compute how many bytes there are between the start of the cluster
+	 * containing offset and the end of the l2 slice that contains
+	 * the entry pointing to it */
+	bytes_available = ((u64)(
+		qcow_data->l2_slice_size -
+		loop_file_fmt_qcow_offset_to_l2_slice_index(qcow_data, offset))
+	) << qcow_data->cluster_bits;
+
+	if (bytes_needed > bytes_available) {
+		bytes_needed = bytes_available;
+	}
+
+	*cluster_offset = 0;
+
+	/* seek to the l2 offset in the l1 table */
+	l1_index = loop_file_fmt_qcow_offset_to_l1_index(qcow_data, offset);
+	if (l1_index >= qcow_data->l1_size) {
+		type = QCOW_CLUSTER_UNALLOCATED;
+		goto out;
+	}
+
+	l2_offset = qcow_data->l1_table[l1_index] & L1E_OFFSET_MASK;
+	if (!l2_offset) {
+		type = QCOW_CLUSTER_UNALLOCATED;
+		goto out;
+	}
+
+	if (loop_file_fmt_qcow_offset_into_cluster(qcow_data, l2_offset)) {
+		printk_ratelimited(KERN_ERR "loop_file_fmt_qcow: L2 table "
+			"offset %llx unaligned (L1 index: %llx)", l2_offset,
+			l1_index);
+		return -EIO;
+	}
+
+	/* load the l2 slice in memory */
+	ret = __loop_file_fmt_qcow_cluster_l2_load(lo_fmt, offset, l2_offset,
+		&l2_slice);
+	if (ret < 0) {
+		return ret;
+	}
+
+	/* find the cluster offset for the given disk offset */
+	l2_index = loop_file_fmt_qcow_offset_to_l2_slice_index(qcow_data,
+		offset);
+	*cluster_offset = be64_to_cpu(l2_slice[l2_index]);
+
+	nb_clusters = loop_file_fmt_qcow_size_to_clusters(qcow_data,
+		bytes_needed);
+	/* bytes_needed <= *bytes + offset_in_cluster, both of which are
+	 * unsigned integers; the minimum cluster size is 512, so this
+	 * assertion is always true */
+	ASSERT(nb_clusters <= INT_MAX);
+
+	type = loop_file_fmt_qcow_get_cluster_type(lo_fmt, *cluster_offset);
+	if (qcow_data->qcow_version < 3 && (
+			type == QCOW_CLUSTER_ZERO_PLAIN ||
+			type == QCOW_CLUSTER_ZERO_ALLOC)) {
+		printk_ratelimited(KERN_ERR "loop_file_fmt_qcow: zero cluster "
+			"entry found in pre-v3 image (L2 offset: %llx, "
+			"L2 index: %x)\n", l2_offset, l2_index);
+		ret = -EIO;
+		goto fail;
+	}
+	switch (type) {
+	case QCOW_CLUSTER_COMPRESSED:
+		if (loop_file_fmt_qcow_has_data_file(lo_fmt)) {
+			printk_ratelimited(KERN_ERR "loop_file_fmt_qcow: "
+				"compressed cluster entry found in image with "
+				"external data file (L2 offset: %llx, "
+				"L2 index: %x)", l2_offset, l2_index);
+			ret = -EIO;
+			goto fail;
+		}
+		/* Compressed clusters can only be processed one by one */
+		c = 1;
+		*cluster_offset &= L2E_COMPRESSED_OFFSET_SIZE_MASK;
+		break;
+	case QCOW_CLUSTER_ZERO_PLAIN:
+	case QCOW_CLUSTER_UNALLOCATED:
+		/* how many empty clusters ? */
+		c = __loop_file_fmt_qcow_cluster_count_contiguous_unallocated(
+			lo_fmt, nb_clusters, &l2_slice[l2_index], type);
+		*cluster_offset = 0;
+		break;
+	case QCOW_CLUSTER_ZERO_ALLOC:
+	case QCOW_CLUSTER_NORMAL:
+		/* how many allocated clusters ? */
+		c = __loop_file_fmt_qcow_cluster_count_contiguous(lo_fmt,
+			nb_clusters, qcow_data->cluster_size,
+			&l2_slice[l2_index], QCOW_OFLAG_ZERO);
+		*cluster_offset &= L2E_OFFSET_MASK;
+		if (loop_file_fmt_qcow_offset_into_cluster(qcow_data,
+				*cluster_offset)) {
+			printk_ratelimited(KERN_ERR "loop_file_fmt_qcow: "
+				"cluster allocation offset %llx unaligned "
+				"(L2 offset: %llx, L2 index: %x)\n",
+				*cluster_offset, l2_offset, l2_index);
+			ret = -EIO;
+			goto fail;
+		}
+		if (loop_file_fmt_qcow_has_data_file(lo_fmt) &&
+			*cluster_offset != offset - offset_in_cluster) {
+			printk_ratelimited(KERN_ERR "loop_file_fmt_qcow: "
+				"external data file host cluster offset %llx "
+				"does not match guest cluster offset: %llx, "
+				"L2 index: %x)", *cluster_offset,
+				offset - offset_in_cluster, l2_index);
+			ret = -EIO;
+			goto fail;
+		}
+		break;
+	default:
+		BUG();
+	}
+
+	loop_file_fmt_qcow_cache_put(lo_fmt, (void **) &l2_slice);
+
+	bytes_available = (s64) c * qcow_data->cluster_size;
+
+out:
+	if (bytes_available > bytes_needed) {
+		bytes_available = bytes_needed;
+	}
+
+	/* bytes_available <= bytes_needed <= *bytes + offset_in_cluster;
+	 * subtracting offset_in_cluster will therefore definitely yield
+	 * something not exceeding UINT_MAX */
+	ASSERT(bytes_available - offset_in_cluster <= UINT_MAX);
+	*bytes = bytes_available - offset_in_cluster;
+
+	return type;
+
+fail:
+	loop_file_fmt_qcow_cache_put(lo_fmt, (void **) &l2_slice);
+	return ret;
+}
diff --git a/loop_file_fmt_qcow_cluster.h b/loop_file_fmt_qcow_cluster.h
new file mode 100644
index 0000000..d62e331
--- /dev/null
+++ b/loop_file_fmt_qcow_cluster.h
@@ -0,0 +1,23 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * loop_file_fmt_qcow_cluster.h
+ *
+ * Ported QCOW2 implementation of the QEMU project (GPL-2.0):
+ * Cluster calculation and lookup for the QCOW2 format.
+ *
+ * The copyright (C) 2004-2006 of the original code is owned by Fabrice Bellard.
+ *
+ * Copyright (C) 2019 Manuel Bentele <development@manuel-bentele.de>
+ */
+
+#ifndef _LINUX_LOOP_FILE_FMT_QCOW_CLUSTER_H
+#define _LINUX_LOOP_FILE_FMT_QCOW_CLUSTER_H
+
+#include "loop_file_fmt.h"
+
+extern int loop_file_fmt_qcow_cluster_get_offset(struct loop_file_fmt *lo_fmt,
+						 u64 offset,
+						 unsigned int *bytes,
+						 u64 *cluster_offset);
+
+#endif
diff --git a/loop_file_fmt_qcow_main.c b/loop_file_fmt_qcow_main.c
new file mode 100644
index 0000000..4fb786b
--- /dev/null
+++ b/loop_file_fmt_qcow_main.c
@@ -0,0 +1,945 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * loop_file_fmt_qcow.c
+ *
+ * QCOW file format driver for the loop device module.
+ *
+ * Copyright (C) 2019 Manuel Bentele <development@manuel-bentele.de>
+ */
+
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/init.h>
+#include <linux/fs.h>
+#include <linux/types.h>
+#include <linux/limits.h>
+#include <linux/blkdev.h>
+#include <linux/bio.h>
+#include <linux/bvec.h>
+#include <linux/mutex.h>
+#include <linux/uio.h>
+#include <linux/string.h>
+#include <linux/vmalloc.h>
+#include <linux/zlib.h>
+
+#include "loop_file_fmt.h"
+#include "loop_file_fmt_qcow_main.h"
+#include "loop_file_fmt_qcow_cache.h"
+#include "loop_file_fmt_qcow_cluster.h"
+
+static int __qcow_file_fmt_header_read(struct loop_file_fmt *lo_fmt,
+	struct loop_file_fmt_qcow_header *header)
+{
+	struct loop_device *lo = loop_file_fmt_get_lo(lo_fmt);
+	ssize_t len;
+	loff_t offset;
+	int ret = 0;
+
+	/* read QCOW header */
+	offset = 0;
+	len = kernel_read(lo->lo_backing_file, header, sizeof(*header),
+		&offset);
+	if (len < 0) {
+		printk(KERN_ERR "loop_file_fmt_qcow: could not read QCOW "
+			"header");
+		return len;
+	}
+
+	header->magic = be32_to_cpu(header->magic);
+	header->version = be32_to_cpu(header->version);
+	header->backing_file_offset = be64_to_cpu(header->backing_file_offset);
+	header->backing_file_size = be32_to_cpu(header->backing_file_size);
+	header->cluster_bits = be32_to_cpu(header->cluster_bits);
+	header->size = be64_to_cpu(header->size);
+	header->crypt_method = be32_to_cpu(header->crypt_method);
+	header->l1_size = be32_to_cpu(header->l1_size);
+	header->l1_table_offset = be64_to_cpu(header->l1_table_offset);
+	header->refcount_table_offset =
+		be64_to_cpu(header->refcount_table_offset);
+	header->refcount_table_clusters =
+		be32_to_cpu(header->refcount_table_clusters);
+	header->nb_snapshots = be32_to_cpu(header->nb_snapshots);
+	header->snapshots_offset = be64_to_cpu(header->snapshots_offset);
+
+	/* check QCOW file format and header version */
+	if (header->magic != QCOW_MAGIC) {
+		printk(KERN_ERR "loop_file_fmt_qcow: image is not in QCOW "
+			"format");
+		return -EINVAL;
+	}
+
+	if (header->version < 2 || header->version > 3) {
+		printk(KERN_ERR "loop_file_fmt_qcow: unsupported QCOW version "
+			"%d", header->version);
+		return -ENOTSUPP;
+	}
+
+	/* initialize version 3 header fields */
+	if (header->version == 2) {
+		header->incompatible_features =  0;
+		header->compatible_features   =  0;
+		header->autoclear_features    =  0;
+		header->refcount_order        =  4;
+		header->header_length         = 72;
+	} else {
+		header->incompatible_features =
+			be64_to_cpu(header->incompatible_features);
+		header->compatible_features =
+			be64_to_cpu(header->compatible_features);
+		header->autoclear_features =
+			be64_to_cpu(header->autoclear_features);
+		header->refcount_order = be32_to_cpu(header->refcount_order);
+		header->header_length = be32_to_cpu(header->header_length);
+
+		if (header->header_length < 104) {
+			printk(KERN_ERR "loop_file_fmt_qcow: QCOW header too "
+				"short");
+			return -EINVAL;
+		}
+	}
+
+	return ret;
+}
+
+static int __qcow_file_fmt_validate_table(struct loop_file_fmt *lo_fmt,
+	u64 offset, u64 entries, size_t entry_len, s64 max_size_bytes,
+	const char *table_name)
+{
+	struct loop_file_fmt_qcow_data *qcow_data = lo_fmt->private_data;
+
+	if (entries > max_size_bytes / entry_len) {
+		printk(KERN_INFO "loop_file_fmt_qcow: %s too large",
+			table_name);
+		return -EFBIG;
+	}
+
+	/* Use signed S64_MAX as the maximum even for u64 header fields,
+	 * because values will be passed to qemu functions taking s64. */
+	if ((S64_MAX - entries * entry_len < offset) || (
+		loop_file_fmt_qcow_offset_into_cluster(qcow_data, offset) != 0)
+	) {
+		printk(KERN_INFO "loop_file_fmt_qcow: %s offset invalid",
+			table_name);
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+static inline loff_t __qcow_file_fmt_rq_get_pos(struct loop_file_fmt *lo_fmt,
+						struct request *rq)
+{
+	struct loop_device *lo = loop_file_fmt_get_lo(lo_fmt);
+	return ((loff_t) blk_rq_pos(rq) << 9) + lo->lo_offset;
+}
+
+static int __qcow_file_fmt_compression_init(struct loop_file_fmt *lo_fmt)
+{
+	struct loop_file_fmt_qcow_data *qcow_data = lo_fmt->private_data;
+	int ret = 0;
+
+	qcow_data->strm = kzalloc(sizeof(*qcow_data->strm), GFP_KERNEL);
+	if (!qcow_data->strm) {
+		ret = -ENOMEM;
+		goto out;
+	}
+
+	qcow_data->strm->workspace = vzalloc(zlib_inflate_workspacesize());
+	if (!qcow_data->strm->workspace) {
+		ret = -ENOMEM;
+		goto out_free_strm;
+	}
+
+	return ret;
+
+out_free_strm:
+	kfree(qcow_data->strm);
+out:
+	return ret;
+}
+
+static void __qcow_file_fmt_compression_exit(struct loop_file_fmt *lo_fmt)
+{
+	struct loop_file_fmt_qcow_data *qcow_data = lo_fmt->private_data;
+
+	if (qcow_data->strm->workspace)
+		vfree(qcow_data->strm->workspace);
+
+	if (qcow_data->strm)
+		kfree(qcow_data->strm);
+}
+
+#ifdef CONFIG_DEBUG_FS
+static void __qcow_file_fmt_header_to_buf(struct loop_file_fmt *lo_fmt,
+	const struct loop_file_fmt_qcow_header *header)
+{
+	struct loop_file_fmt_qcow_data *qcow_data = lo_fmt->private_data;
+	char *header_buf = qcow_data->dbgfs_file_qcow_header_buf;
+	ssize_t len = 0;
+
+	len += sprintf(header_buf + len, "magic: %d\n",
+		header->magic);
+	len += sprintf(header_buf + len, "version: %d\n",
+		header->version);
+	len += sprintf(header_buf + len, "backing_file_offset: %lld\n",
+		header->backing_file_offset);
+	len += sprintf(header_buf + len, "backing_file_size: %d\n",
+		header->backing_file_size);
+	len += sprintf(header_buf + len, "cluster_bits: %d\n",
+		header->cluster_bits);
+	len += sprintf(header_buf + len, "size: %lld\n",
+		header->size);
+	len += sprintf(header_buf + len, "crypt_method: %d\n",
+		header->crypt_method);
+	len += sprintf(header_buf + len, "l1_size: %d\n",
+		header->l1_size);
+	len += sprintf(header_buf + len, "l1_table_offset: %lld\n",
+		header->l1_table_offset);
+	len += sprintf(header_buf + len, "refcount_table_offset: %lld\n",
+		header->refcount_table_offset);
+	len += sprintf(header_buf + len, "refcount_table_clusters: %d\n",
+		header->refcount_table_clusters);
+	len += sprintf(header_buf + len, "nb_snapshots: %d\n",
+		header->nb_snapshots);
+	len += sprintf(header_buf + len, "snapshots_offset: %lld\n",
+		header->snapshots_offset);
+
+	if (header->version == 3) {
+		len += sprintf(header_buf + len,
+			"incompatible_features: %lld\n",
+			header->incompatible_features);
+		len += sprintf(header_buf + len,
+			"compatible_features: %lld\n",
+			header->compatible_features);
+		len += sprintf(header_buf + len,
+			"autoclear_features: %lld\n",
+			header->autoclear_features);
+		len += sprintf(header_buf + len,
+			"refcount_order: %d\n",
+			header->refcount_order);
+		len += sprintf(header_buf + len,
+			"header_length: %d\n",
+			header->header_length);
+	}
+
+	ASSERT(len < QCOW_HEADER_BUF_LEN);
+}
+
+static ssize_t __qcow_file_fmt_dbgfs_hdr_read(struct file *file,
+	char __user *buf, size_t size, loff_t *ppos)
+{
+	struct loop_file_fmt *lo_fmt = file->private_data;
+	struct loop_file_fmt_qcow_data *qcow_data = lo_fmt->private_data;
+	char *header_buf = qcow_data->dbgfs_file_qcow_header_buf;
+
+	return simple_read_from_buffer(buf, size, ppos, header_buf,
+		strlen(header_buf));
+}
+
+static const struct file_operations qcow_file_fmt_dbgfs_hdr_fops = {
+	.open = simple_open,
+	.read = __qcow_file_fmt_dbgfs_hdr_read
+};
+
+static ssize_t __qcow_file_fmt_dbgfs_ofs_read(struct file *file,
+	char __user *buf, size_t size, loff_t *ppos)
+{
+	struct loop_file_fmt *lo_fmt = file->private_data;
+	struct loop_file_fmt_qcow_data *qcow_data = lo_fmt->private_data;
+	unsigned int cur_bytes = 1;
+	u64 offset = 0;
+	u64 cluster_offset = 0;
+	s64 offset_in_cluster = 0;
+	ssize_t len = 0;
+	int ret = 0;
+
+	/* read the share debugfs offset */
+	ret = mutex_lock_interruptible(&qcow_data->dbgfs_qcow_offset_mutex);
+	if (ret)
+		return ret;
+
+	offset = qcow_data->dbgfs_qcow_offset;
+	mutex_unlock(&qcow_data->dbgfs_qcow_offset_mutex);
+
+	/* calculate and print the cluster offset */
+	ret = loop_file_fmt_qcow_cluster_get_offset(lo_fmt,
+		offset, &cur_bytes, &cluster_offset);
+	if (ret < 0)
+		return -EINVAL;
+
+	offset_in_cluster = loop_file_fmt_qcow_offset_into_cluster(qcow_data,
+		offset);
+
+	len = sprintf(qcow_data->dbgfs_file_qcow_cluster_buf,
+		"offset: %lld\ncluster_offset: %lld\noffset_in_cluster: %lld\n",
+		offset, cluster_offset, offset_in_cluster);
+
+	ASSERT(len < QCOW_CLUSTER_BUF_LEN);
+
+	return simple_read_from_buffer(buf, size, ppos,
+		qcow_data->dbgfs_file_qcow_cluster_buf, len);
+}
+
+static ssize_t __qcow_file_fmt_dbgfs_ofs_write(struct file *file,
+	const char __user *buf, size_t size, loff_t *ppos)
+{
+	struct loop_file_fmt *lo_fmt = file->private_data;
+	struct loop_file_fmt_qcow_data *qcow_data = lo_fmt->private_data;
+	ssize_t len = 0;
+	int ret = 0;
+
+	if (*ppos > QCOW_OFFSET_BUF_LEN || size > QCOW_OFFSET_BUF_LEN)
+		return -EINVAL;
+
+	len = simple_write_to_buffer(qcow_data->dbgfs_file_qcow_offset_buf,
+		QCOW_OFFSET_BUF_LEN, ppos, buf, size);
+	if (len < 0)
+		return len;
+
+	qcow_data->dbgfs_file_qcow_offset_buf[len] = '\0';
+
+	ret = mutex_lock_interruptible(&qcow_data->dbgfs_qcow_offset_mutex);
+	if (ret)
+		return ret;
+
+	ret = kstrtou64(qcow_data->dbgfs_file_qcow_offset_buf, 10,
+		&qcow_data->dbgfs_qcow_offset);
+	if (ret < 0)
+		goto out;
+
+	ret = len;
+out:
+	mutex_unlock(&qcow_data->dbgfs_qcow_offset_mutex);
+	return ret;
+}
+
+static const struct file_operations qcow_file_fmt_dbgfs_ofs_fops = {
+	.open = simple_open,
+	.read = __qcow_file_fmt_dbgfs_ofs_read,
+	.write = __qcow_file_fmt_dbgfs_ofs_write
+};
+
+static int __qcow_file_fmt_dbgfs_init(struct loop_file_fmt *lo_fmt)
+{
+	struct loop_file_fmt_qcow_data *qcow_data = lo_fmt->private_data;
+	struct loop_device *lo = loop_file_fmt_get_lo(lo_fmt);
+	int ret = 0;
+
+	qcow_data->dbgfs_dir = debugfs_create_dir("QCOW", lo->lo_dbgfs_dir);
+	if (IS_ERR_OR_NULL(qcow_data->dbgfs_dir)) {
+		ret = -ENODEV;
+		goto out;
+	}
+
+	qcow_data->dbgfs_file_qcow_header = debugfs_create_file("header",
+		S_IRUGO, qcow_data->dbgfs_dir, lo_fmt,
+		&qcow_file_fmt_dbgfs_hdr_fops);
+	if (IS_ERR_OR_NULL(qcow_data->dbgfs_file_qcow_header)) {
+		ret = -ENODEV;
+		goto out_free_dbgfs_dir;
+	}
+
+	qcow_data->dbgfs_file_qcow_offset = debugfs_create_file("offset",
+		S_IRUGO | S_IWUSR, qcow_data->dbgfs_dir, lo_fmt,
+		&qcow_file_fmt_dbgfs_ofs_fops);
+	if (IS_ERR_OR_NULL(qcow_data->dbgfs_file_qcow_offset)) {
+		qcow_data->dbgfs_file_qcow_offset = NULL;
+		ret = -ENODEV;
+		goto out_free_dbgfs_hdr;
+	}
+
+	qcow_data->dbgfs_qcow_offset = 0;
+	mutex_init(&qcow_data->dbgfs_qcow_offset_mutex);
+
+	return ret;
+
+out_free_dbgfs_hdr:
+	debugfs_remove(qcow_data->dbgfs_file_qcow_header);
+	qcow_data->dbgfs_file_qcow_header = NULL;
+out_free_dbgfs_dir:
+	debugfs_remove(qcow_data->dbgfs_dir);
+	qcow_data->dbgfs_dir = NULL;
+out:
+	return ret;
+}
+
+static void __qcow_file_fmt_dbgfs_exit(struct loop_file_fmt *lo_fmt)
+{
+	struct loop_file_fmt_qcow_data *qcow_data = lo_fmt->private_data;
+
+	if (qcow_data->dbgfs_file_qcow_offset)
+		debugfs_remove(qcow_data->dbgfs_file_qcow_offset);
+
+	mutex_destroy(&qcow_data->dbgfs_qcow_offset_mutex);
+
+	if (qcow_data->dbgfs_file_qcow_header)
+		debugfs_remove(qcow_data->dbgfs_file_qcow_header);
+
+	if (qcow_data->dbgfs_dir)
+		debugfs_remove(qcow_data->dbgfs_dir);
+}
+#endif
+
+static int qcow_file_fmt_init(struct loop_file_fmt *lo_fmt)
+{
+	struct loop_file_fmt_qcow_data *qcow_data;
+	struct loop_device *lo = loop_file_fmt_get_lo(lo_fmt);
+	struct loop_file_fmt_qcow_header header;
+	u64 l1_vm_state_index;
+	u64 l2_cache_size;
+	u64 l2_cache_entry_size;
+	ssize_t len;
+	unsigned int i;
+	int ret = 0;
+
+	/* allocate memory for saving QCOW file format data */
+	qcow_data = kzalloc(sizeof(*qcow_data), GFP_KERNEL);
+	if (!qcow_data)
+		return -ENOMEM;
+
+	lo_fmt->private_data = qcow_data;
+
+	/* read the QCOW file header */
+	ret = __qcow_file_fmt_header_read(lo_fmt, &header);
+	if (ret)
+		goto free_qcow_data;
+
+	/* save information of the header fields in human readable format in
+	 * a file buffer to access it with debugfs */
+#ifdef CONFIG_DEBUG_FS
+	__qcow_file_fmt_header_to_buf(lo_fmt, &header);
+#endif
+
+	qcow_data->qcow_version = header.version;
+
+	/* Initialise cluster size */
+	if (header.cluster_bits < QCOW_MIN_CLUSTER_BITS
+		|| header.cluster_bits > QCOW_MAX_CLUSTER_BITS) {
+		printk(KERN_ERR "loop_file_fmt_qcow: unsupported cluster "
+			"size: 2^%d", header.cluster_bits);
+		ret = -EINVAL;
+		goto free_qcow_data;
+	}
+
+	qcow_data->cluster_bits = header.cluster_bits;
+	qcow_data->cluster_size = 1 << qcow_data->cluster_bits;
+	qcow_data->cluster_sectors = 1 <<
+		(qcow_data->cluster_bits - SECTOR_SHIFT);
+
+	if (header.header_length > qcow_data->cluster_size) {
+		printk(KERN_ERR "loop_file_fmt_qcow: QCOW header exceeds "
+			"cluster size");
+		ret = -EINVAL;
+		goto free_qcow_data;
+	}
+
+	if (header.backing_file_offset > qcow_data->cluster_size) {
+		printk(KERN_ERR "loop_file_fmt_qcow: invalid backing file "
+			"offset");
+		ret = -EINVAL;
+		goto free_qcow_data;
+	}
+
+	if (header.backing_file_offset) {
+		printk(KERN_ERR "loop_file_fmt_qcow: backing file support not "
+			"available");
+		ret = -ENOTSUPP;
+		goto free_qcow_data;
+	}
+
+	/* handle feature bits */
+	qcow_data->incompatible_features = header.incompatible_features;
+	qcow_data->compatible_features = header.compatible_features;
+	qcow_data->autoclear_features = header.autoclear_features;
+
+	if (qcow_data->incompatible_features & QCOW_INCOMPAT_DIRTY) {
+		printk(KERN_ERR "loop_file_fmt_qcow: image contains "
+			"inconsistent refcounts");
+		ret = -EACCES;
+		goto free_qcow_data;
+	}
+
+	if (qcow_data->incompatible_features & QCOW_INCOMPAT_CORRUPT) {
+		printk(KERN_ERR "loop_file_fmt_qcow: image is corrupt; cannot "
+			"be opened read/write");
+		ret = -EACCES;
+		goto free_qcow_data;
+	}
+
+	if (qcow_data->incompatible_features & QCOW_INCOMPAT_DATA_FILE) {
+		printk(KERN_ERR "loop_file_fmt_qcow: clusters in the external "
+			"data file are not refcounted");
+		ret = -EACCES;
+		goto free_qcow_data;
+	}
+
+	/* Check support for various header values */
+	if (header.refcount_order > 6) {
+		printk(KERN_ERR "loop_file_fmt_qcow: reference count entry "
+			"width too large; may not exceed 64 bits");
+		ret = -EINVAL;
+		goto free_qcow_data;
+	}
+	qcow_data->refcount_order = header.refcount_order;
+	qcow_data->refcount_bits = 1 << qcow_data->refcount_order;
+	qcow_data->refcount_max = U64_C(1) << (qcow_data->refcount_bits - 1);
+	qcow_data->refcount_max += qcow_data->refcount_max - 1;
+
+	qcow_data->crypt_method_header = header.crypt_method;
+	if (qcow_data->crypt_method_header) {
+		printk(KERN_ERR "loop_file_fmt_qcow: encryption support not "
+			"available");
+		ret = -ENOTSUPP;
+		goto free_qcow_data;
+	}
+
+	/* L2 is always one cluster */
+	qcow_data->l2_bits = qcow_data->cluster_bits - 3;
+	qcow_data->l2_size = 1 << qcow_data->l2_bits;
+	/* 2^(qcow_data->refcount_order - 3) is the refcount width in bytes */
+	qcow_data->refcount_block_bits = qcow_data->cluster_bits -
+		(qcow_data->refcount_order - 3);
+	qcow_data->refcount_block_size = 1 << qcow_data->refcount_block_bits;
+	qcow_data->size = header.size;
+	qcow_data->csize_shift = (62 - (qcow_data->cluster_bits - 8));
+	qcow_data->csize_mask = (1 << (qcow_data->cluster_bits - 8)) - 1;
+	qcow_data->cluster_offset_mask = (1LL << qcow_data->csize_shift) - 1;
+
+	qcow_data->refcount_table_offset = header.refcount_table_offset;
+	qcow_data->refcount_table_size = header.refcount_table_clusters <<
+		(qcow_data->cluster_bits - 3);
+
+	if (header.refcount_table_clusters == 0) {
+		printk(KERN_ERR "loop_file_fmt_qcow: image does not contain a "
+			"reference count table");
+		ret = -EINVAL;
+		goto free_qcow_data;
+	}
+
+	ret = __qcow_file_fmt_validate_table(lo_fmt,
+		qcow_data->refcount_table_offset,
+		header.refcount_table_clusters, qcow_data->cluster_size,
+		QCOW_MAX_REFTABLE_SIZE, "Reference count table");
+	if (ret < 0) {
+		goto free_qcow_data;
+	}
+
+	/* The total size in bytes of the snapshot table is checked in
+	 * qcow2_read_snapshots() because the size of each snapshot is
+	 * variable and we don't know it yet.
+	 * Here we only check the offset and number of snapshots. */
+	ret = __qcow_file_fmt_validate_table(lo_fmt, header.snapshots_offset,
+		header.nb_snapshots,
+		sizeof(struct loop_file_fmt_qcow_snapshot_header),
+		sizeof(struct loop_file_fmt_qcow_snapshot_header) *
+		QCOW_MAX_SNAPSHOTS, "Snapshot table");
+	if (ret < 0) {
+		goto free_qcow_data;
+	}
+
+	/* read the level 1 table */
+	ret = __qcow_file_fmt_validate_table(lo_fmt, header.l1_table_offset,
+		header.l1_size, sizeof(u64), QCOW_MAX_L1_SIZE,
+		"Active L1 table");
+	if (ret < 0) {
+		goto free_qcow_data;
+	}
+	qcow_data->l1_size = header.l1_size;
+	qcow_data->l1_table_offset = header.l1_table_offset;
+
+	l1_vm_state_index = loop_file_fmt_qcow_size_to_l1(qcow_data,
+		header.size);
+	if (l1_vm_state_index > INT_MAX) {
+		printk(KERN_ERR "loop_file_fmt_qcow: image is too big");
+		ret = -EFBIG;
+		goto free_qcow_data;
+	}
+	qcow_data->l1_vm_state_index = l1_vm_state_index;
+
+	/* the L1 table must contain at least enough entries to put header.size
+	 * bytes */
+	if (qcow_data->l1_size < qcow_data->l1_vm_state_index) {
+		printk(KERN_ERR "loop_file_fmt_qcow: L1 table is too small");
+		ret = -EINVAL;
+		goto free_qcow_data;
+	}
+
+	if (qcow_data->l1_size > 0) {
+		qcow_data->l1_table = vzalloc(round_up(qcow_data->l1_size *
+			sizeof(u64), 512));
+		if (qcow_data->l1_table == NULL) {
+			printk(KERN_ERR "loop_file_fmt_qcow: could not "
+				"allocate L1 table");
+			ret = -ENOMEM;
+			goto free_qcow_data;
+		}
+		len = kernel_read(lo->lo_backing_file, qcow_data->l1_table,
+			qcow_data->l1_size * sizeof(u64),
+			&qcow_data->l1_table_offset);
+		if (len < 0) {
+			printk(KERN_ERR "loop_file_fmt_qcow: could not read L1 "
+				"table");
+			ret = len;
+			goto free_l1_table;
+		}
+		for (i = 0; i < qcow_data->l1_size; i++) {
+			qcow_data->l1_table[i] =
+				be64_to_cpu(qcow_data->l1_table[i]);
+		}
+	}
+
+	/* Internal snapshots */
+	qcow_data->snapshots_offset = header.snapshots_offset;
+	qcow_data->nb_snapshots = header.nb_snapshots;
+
+	if (qcow_data->nb_snapshots > 0) {
+		printk(KERN_ERR "loop_file_fmt_qcow: snapshots support not "
+			"available");
+		ret = -ENOTSUPP;
+		goto free_l1_table;
+	}
+
+
+	/* create cache for L2 */
+	l2_cache_size =  qcow_data->size / (qcow_data->cluster_size / 8);
+	l2_cache_entry_size = min(qcow_data->cluster_size, (int)4096);
+
+	/* limit the L2 size to maximum QCOW_DEFAULT_L2_CACHE_MAX_SIZE */
+	l2_cache_size = min(l2_cache_size, (u64)QCOW_DEFAULT_L2_CACHE_MAX_SIZE);
+
+	/* calculate the number of cache tables */
+	l2_cache_size /= l2_cache_entry_size;
+	if (l2_cache_size < QCOW_MIN_L2_CACHE_SIZE) {
+		l2_cache_size = QCOW_MIN_L2_CACHE_SIZE;
+	}
+
+	if (l2_cache_size > INT_MAX) {
+		printk(KERN_ERR "loop_file_fmt_qcow: L2 cache size too big");
+		ret = -EINVAL;
+		goto free_l1_table;
+	}
+
+	qcow_data->l2_slice_size = l2_cache_entry_size / sizeof(u64);
+
+	qcow_data->l2_table_cache = loop_file_fmt_qcow_cache_create(lo_fmt,
+		l2_cache_size, l2_cache_entry_size);
+	if (!qcow_data->l2_table_cache) {
+		ret = -ENOMEM;
+		goto free_l1_table;
+	}
+
+	/* initialize compression support */
+	ret = __qcow_file_fmt_compression_init(lo_fmt);
+	if (ret < 0)
+		goto free_l2_cache;
+
+	/* initialize debugfs entries */
+#ifdef CONFIG_DEBUG_FS
+	ret = __qcow_file_fmt_dbgfs_init(lo_fmt);
+	if (ret < 0)
+		goto free_l2_cache;
+#endif
+
+	return ret;
+
+free_l2_cache:
+	loop_file_fmt_qcow_cache_destroy(lo_fmt);
+free_l1_table:
+	vfree(qcow_data->l1_table);
+free_qcow_data:
+	kfree(qcow_data);
+	lo_fmt->private_data = NULL;
+	return ret;
+}
+
+static void qcow_file_fmt_exit(struct loop_file_fmt *lo_fmt)
+{
+	struct loop_file_fmt_qcow_data *qcow_data = lo_fmt->private_data;
+
+#ifdef CONFIG_DEBUG_FS
+	__qcow_file_fmt_dbgfs_exit(lo_fmt);
+#endif
+
+	__qcow_file_fmt_compression_exit(lo_fmt);
+
+	if (qcow_data->l1_table) {
+		vfree(qcow_data->l1_table);
+	}
+
+	if (qcow_data->l2_table_cache) {
+		loop_file_fmt_qcow_cache_destroy(lo_fmt);
+	}
+
+	if (qcow_data) {
+		kfree(qcow_data);
+		lo_fmt->private_data = NULL;
+	}
+}
+
+static ssize_t __qcow_file_fmt_buffer_decompress(struct loop_file_fmt *lo_fmt,
+						 void *dest,
+						 size_t dest_size,
+						 const void *src,
+						 size_t src_size)
+{
+	struct loop_file_fmt_qcow_data *qcow_data = lo_fmt->private_data;
+	int ret = 0;
+
+	qcow_data->strm->avail_in = src_size;
+	qcow_data->strm->next_in = (void *) src;
+	qcow_data->strm->avail_out = dest_size;
+	qcow_data->strm->next_out = dest;
+
+	ret = zlib_inflateInit2(qcow_data->strm, -12);
+	if (ret != Z_OK) {
+		return -1;
+	}
+
+	ret = zlib_inflate(qcow_data->strm, Z_FINISH);
+	if ((ret != Z_STREAM_END && ret != Z_BUF_ERROR)
+		|| qcow_data->strm->avail_out != 0) {
+		/* We approve Z_BUF_ERROR because we need @dest buffer to be
+		 * filled, but @src buffer may be processed partly (because in
+		 * qcow2 we know size of compressed data with precision of one
+		 * sector) */
+		ret = -1;
+	}
+
+	zlib_inflateEnd(qcow_data->strm);
+
+	return ret;
+}
+
+static int __qcow_file_fmt_read_compressed(struct loop_file_fmt *lo_fmt,
+					   struct bio_vec *bvec,
+					   u64 file_cluster_offset,
+					   u64 offset,
+					   u64 bytes,
+					   u64 bytes_done)
+{
+	struct loop_file_fmt_qcow_data *qcow_data = lo_fmt->private_data;
+	struct loop_device *lo = loop_file_fmt_get_lo(lo_fmt);
+	int ret = 0, csize, nb_csectors;
+	u64 coffset;
+	u8 *in_buf, *out_buf;
+	ssize_t len;
+	void *data;
+	unsigned long irq_flags;
+	int offset_in_cluster = loop_file_fmt_qcow_offset_into_cluster(
+		qcow_data, offset);
+
+	coffset = file_cluster_offset & qcow_data->cluster_offset_mask;
+	nb_csectors = ((file_cluster_offset >> qcow_data->csize_shift) &
+		qcow_data->csize_mask) + 1;
+	csize = nb_csectors * QCOW_COMPRESSED_SECTOR_SIZE -
+		(coffset & ~QCOW_COMPRESSED_SECTOR_MASK);
+
+	in_buf = vmalloc(csize);
+	if (!in_buf) {
+		return -ENOMEM;
+	}
+
+	out_buf = vmalloc(qcow_data->cluster_size);
+	if (!out_buf) {
+		ret = -ENOMEM;
+		goto out_free_in_buf;
+	}
+
+	len = kernel_read(lo->lo_backing_file, in_buf, csize, &coffset);
+	if (len < 0) {
+		ret = len;
+		goto out_free_out_buf;
+	}
+
+	if (__qcow_file_fmt_buffer_decompress(lo_fmt, out_buf,
+		qcow_data->cluster_size, in_buf, csize) < 0) {
+		ret = -EIO;
+		goto out_free_out_buf;
+	}
+
+	ASSERT(bytes <= bvec->bv_len);
+	data = bvec_kmap_irq(bvec, &irq_flags) + bytes_done;
+	memcpy(data, out_buf + offset_in_cluster, bytes);
+	flush_dcache_page(bvec->bv_page);
+	bvec_kunmap_irq(data, &irq_flags);
+
+out_free_out_buf:
+	vfree(out_buf);
+out_free_in_buf:
+	vfree(in_buf);
+
+	return ret;
+}
+
+static int __qcow_file_fmt_read_bvec(struct loop_file_fmt *lo_fmt,
+				     struct bio_vec *bvec,
+				     loff_t *ppos)
+{
+	struct loop_file_fmt_qcow_data *qcow_data = lo_fmt->private_data;
+	struct loop_device *lo = loop_file_fmt_get_lo(lo_fmt);
+	int offset_in_cluster;
+	int ret;
+	unsigned int cur_bytes; /* number of bytes in current iteration */
+	u64 bytes;
+	u64 cluster_offset = 0;
+	u64 bytes_done = 0;
+	void *data;
+	unsigned long irq_flags;
+	ssize_t len;
+	loff_t pos_read;
+
+	bytes = bvec->bv_len;
+
+	while (bytes != 0) {
+
+		/* prepare next request */
+		cur_bytes = bytes;
+
+		ret = loop_file_fmt_qcow_cluster_get_offset(lo_fmt, *ppos,
+			&cur_bytes, &cluster_offset);
+		if (ret < 0) {
+			goto fail;
+		}
+
+		offset_in_cluster = loop_file_fmt_qcow_offset_into_cluster(
+			qcow_data, *ppos);
+
+		switch (ret) {
+		case QCOW_CLUSTER_UNALLOCATED:
+		case QCOW_CLUSTER_ZERO_PLAIN:
+		case QCOW_CLUSTER_ZERO_ALLOC:
+			data = bvec_kmap_irq(bvec, &irq_flags) + bytes_done;
+			memset(data, 0, cur_bytes);
+			flush_dcache_page(bvec->bv_page);
+			bvec_kunmap_irq(data, &irq_flags);
+			break;
+
+		case QCOW_CLUSTER_COMPRESSED:
+			ret = __qcow_file_fmt_read_compressed(lo_fmt, bvec,
+				cluster_offset, *ppos, cur_bytes, bytes_done);
+			if (ret < 0) {
+				goto fail;
+			}
+
+			break;
+
+		case QCOW_CLUSTER_NORMAL:
+			if ((cluster_offset & 511) != 0) {
+				ret = -EIO;
+				goto fail;
+			}
+
+			pos_read = cluster_offset + offset_in_cluster;
+
+			data = bvec_kmap_irq(bvec, &irq_flags) + bytes_done;
+			len = kernel_read(lo->lo_backing_file, data, cur_bytes,
+				&pos_read);
+			flush_dcache_page(bvec->bv_page);
+			bvec_kunmap_irq(data, &irq_flags);
+
+			if (len < 0)
+				return len;
+
+			break;
+
+		default:
+			ret = -EIO;
+			goto fail;
+		}
+
+		bytes -= cur_bytes;
+		*ppos += cur_bytes;
+		bytes_done += cur_bytes;
+	}
+
+	ret = 0;
+
+fail:
+	return ret;
+}
+
+static int qcow_file_fmt_read(struct loop_file_fmt *lo_fmt,
+			      struct request *rq)
+{
+	struct bio_vec bvec;
+	struct req_iterator iter;
+	loff_t pos;
+	int ret = 0;
+
+	pos = __qcow_file_fmt_rq_get_pos(lo_fmt, rq);
+
+	rq_for_each_segment(bvec, rq, iter) {
+		ret = __qcow_file_fmt_read_bvec(lo_fmt, &bvec, &pos);
+		if (ret)
+			return ret;
+
+		cond_resched();
+	}
+
+	return ret;
+}
+
+static loff_t qcow_file_fmt_sector_size(struct loop_file_fmt *lo_fmt)
+{
+	struct loop_file_fmt_qcow_data *qcow_data = lo_fmt->private_data;
+	struct loop_device *lo = loop_file_fmt_get_lo(lo_fmt);
+	loff_t loopsize;
+
+	if (qcow_data->size > 0)
+		loopsize = qcow_data->size;
+	else
+		return 0;
+
+	if (lo->lo_offset > 0)
+		loopsize -= lo->lo_offset;
+
+	if (lo->lo_sizelimit > 0 && lo->lo_sizelimit < loopsize)
+		loopsize = lo->lo_sizelimit;
+
+	/*
+	 * Unfortunately, if we want to do I/O on the device,
+	 * the number of 512-byte sectors has to fit into a sector_t.
+	 */
+	return loopsize >> 9;
+}
+
+static struct loop_file_fmt_ops qcow_file_fmt_ops = {
+	.init = qcow_file_fmt_init,
+	.exit = qcow_file_fmt_exit,
+	.read = qcow_file_fmt_read,
+	.write = NULL,
+	.read_aio = NULL,
+	.write_aio = NULL,
+	.discard = NULL,
+	.flush = NULL,
+	.sector_size = qcow_file_fmt_sector_size
+};
+
+static struct loop_file_fmt_driver qcow_file_fmt_driver = {
+	.name = "QCOW",
+	.file_fmt_type = LO_FILE_FMT_QCOW,
+	.ops = &qcow_file_fmt_ops,
+	.owner = THIS_MODULE
+};
+
+static int __init loop_file_fmt_qcow_init(void)
+{
+	printk(KERN_INFO "loop_file_fmt_qcow: init loop device QCOW file "
+		"format driver");
+	return loop_file_fmt_register_driver(&qcow_file_fmt_driver);
+}
+
+static void __exit loop_file_fmt_qcow_exit(void)
+{
+	printk(KERN_INFO "loop_file_fmt_qcow: exit loop device QCOW file "
+		"format driver");
+	loop_file_fmt_unregister_driver(&qcow_file_fmt_driver);
+}
+
+module_init(loop_file_fmt_qcow_init);
+module_exit(loop_file_fmt_qcow_exit);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Manuel Bentele <development@manuel-bentele.de>");
+MODULE_DESCRIPTION("Loop device QCOW file format driver");
+MODULE_SOFTDEP("pre: loop");
diff --git a/loop_file_fmt_qcow_main.h b/loop_file_fmt_qcow_main.h
new file mode 100644
index 0000000..9e4951f
--- /dev/null
+++ b/loop_file_fmt_qcow_main.h
@@ -0,0 +1,417 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * loop_file_fmt_qcow.h
+ *
+ * QCOW file format driver for the loop device module.
+ *
+ * Ported QCOW2 implementation of the QEMU project (GPL-2.0):
+ * Declarations for the QCOW2 file format.
+ *
+ * The copyright (C) 2004-2006 of the original code is owned by Fabrice Bellard.
+ *
+ * Copyright (C) 2019 Manuel Bentele <development@manuel-bentele.de>
+ */
+
+#ifndef _LINUX_LOOP_FILE_FMT_QCOW_H
+#define _LINUX_LOOP_FILE_FMT_QCOW_H
+
+#include <linux/list.h>
+#include <linux/mutex.h>
+#include <linux/types.h>
+#include <linux/zlib.h>
+
+#ifdef CONFIG_DEBUG_FS
+#include <linux/debugfs.h>
+#endif
+
+#include "loop_file_fmt.h"
+
+#ifdef CONFIG_DEBUG_DRIVER
+#define ASSERT(x)  							\
+do {									\
+	if (!(x)) {							\
+		printk(KERN_EMERG "assertion failed %s: %d: %s\n",	\
+		       __FILE__, __LINE__, #x);				\
+		BUG();							\
+	}								\
+} while (0)
+#else
+#define ASSERT(x) do { } while (0)
+#endif
+
+#define KiB (1024)
+#define MiB (1024 * 1024)
+
+#define QCOW_MAGIC (('Q' << 24) | ('F' << 16) | ('I' << 8) | 0xfb)
+
+#define QCOW_CRYPT_NONE 0
+#define QCOW_CRYPT_AES  1
+#define QCOW_CRYPT_LUKS 2
+
+#define QCOW_MAX_CRYPT_CLUSTERS 32
+#define QCOW_MAX_SNAPSHOTS 65536
+
+/* Field widths in QCOW mean normal cluster offsets cannot reach
+ * 64PB; depending on cluster size, compressed clusters can have a
+ * smaller limit (64PB for up to 16k clusters, then ramps down to
+ * 512TB for 2M clusters).  */
+#define QCOW_MAX_CLUSTER_OFFSET ((1ULL << 56) - 1)
+
+/* 8 MB refcount table is enough for 2 PB images at 64k cluster size
+ * (128 GB for 512 byte clusters, 2 EB for 2 MB clusters) */
+#define QCOW_MAX_REFTABLE_SIZE (8 * MiB)
+
+/* 32 MB L1 table is enough for 2 PB images at 64k cluster size
+ * (128 GB for 512 byte clusters, 2 EB for 2 MB clusters) */
+#define QCOW_MAX_L1_SIZE (32 * MiB)
+
+/* Allow for an average of 1k per snapshot table entry, should be plenty of
+ * space for snapshot names and IDs */
+#define QCOW_MAX_SNAPSHOTS_SIZE (1024 * QCOW_MAX_SNAPSHOTS)
+
+/* Bitmap header extension constraints */
+#define QCOW_MAX_BITMAPS 65535
+#define QCOW_MAX_BITMAP_DIRECTORY_SIZE (1024 * QCOW_MAX_BITMAPS)
+
+/* indicate that the refcount of the referenced cluster is exactly one. */
+#define QCOW_OFLAG_COPIED     (1ULL << 63)
+/* indicate that the cluster is compressed (they never have the copied flag) */
+#define QCOW_OFLAG_COMPRESSED (1ULL << 62)
+/* The cluster reads as all zeros */
+#define QCOW_OFLAG_ZERO (1ULL << 0)
+
+#define QCOW_MIN_CLUSTER_BITS 9
+#define QCOW_MAX_CLUSTER_BITS 21
+
+/* Defined in the qcow2 spec (compressed cluster descriptor) */
+#define QCOW_COMPRESSED_SECTOR_SIZE 512U
+#define QCOW_COMPRESSED_SECTOR_MASK (~(QCOW_COMPRESSED_SECTOR_SIZE - 1))
+
+/* Must be at least 2 to cover COW */
+#define QCOW_MIN_L2_CACHE_SIZE 2 /* cache entries */
+
+/* Must be at least 4 to cover all cases of refcount table growth */
+#define QCOW_MIN_REFCOUNT_CACHE_SIZE 4 /* clusters */
+
+#define QCOW_DEFAULT_L2_CACHE_MAX_SIZE (32 * MiB)
+#define QCOW_DEFAULT_CACHE_CLEAN_INTERVAL 600  /* seconds */
+
+#define QCOW_DEFAULT_CLUSTER_SIZE 65536
+
+/* Buffer size for debugfs file buffer to display QCOW header information */
+#define QCOW_HEADER_BUF_LEN 1024
+
+/* Buffer size for debugfs file buffer to receive and display offset and
+ * cluster offset information */
+#define QCOW_OFFSET_BUF_LEN 32
+#define QCOW_CLUSTER_BUF_LEN 128
+
+struct loop_file_fmt_qcow_header {
+	u32 magic;
+	u32 version;
+	u64 backing_file_offset;
+	u32 backing_file_size;
+	u32 cluster_bits;
+	u64 size; /* in bytes */
+	u32 crypt_method;
+	u32 l1_size;
+	u64 l1_table_offset;
+	u64 refcount_table_offset;
+	u32 refcount_table_clusters;
+	u32 nb_snapshots;
+	u64 snapshots_offset;
+
+	/* The following fields are only valid for version >= 3 */
+	u64 incompatible_features;
+	u64 compatible_features;
+	u64 autoclear_features;
+
+	u32 refcount_order;
+	u32 header_length;
+} __attribute__((packed));
+
+struct loop_file_fmt_qcow_snapshot_header {
+	/* header is 8 byte aligned */
+	u64 l1_table_offset;
+
+	u32 l1_size;
+	u16 id_str_size;
+	u16 name_size;
+
+	u32 date_sec;
+	u32 date_nsec;
+
+	u64 vm_clock_nsec;
+
+	u32 vm_state_size;
+	/* for extension */
+	u32 extra_data_size;
+	/* extra data follows */
+	/* id_str follows */
+	/* name follows  */
+} __attribute__((packed));
+
+enum {
+	QCOW_FEAT_TYPE_INCOMPATIBLE    = 0,
+	QCOW_FEAT_TYPE_COMPATIBLE      = 1,
+	QCOW_FEAT_TYPE_AUTOCLEAR       = 2,
+};
+
+/* incompatible feature bits */
+enum {
+	QCOW_INCOMPAT_DIRTY_BITNR      = 0,
+	QCOW_INCOMPAT_CORRUPT_BITNR    = 1,
+	QCOW_INCOMPAT_DATA_FILE_BITNR  = 2,
+	QCOW_INCOMPAT_DIRTY            = 1 << QCOW_INCOMPAT_DIRTY_BITNR,
+	QCOW_INCOMPAT_CORRUPT          = 1 << QCOW_INCOMPAT_CORRUPT_BITNR,
+	QCOW_INCOMPAT_DATA_FILE        = 1 << QCOW_INCOMPAT_DATA_FILE_BITNR,
+
+	QCOW_INCOMPAT_MASK             = QCOW_INCOMPAT_DIRTY
+					| QCOW_INCOMPAT_CORRUPT
+					| QCOW_INCOMPAT_DATA_FILE,
+};
+
+/* compatible feature bits */
+enum {
+	QCOW_COMPAT_LAZY_REFCOUNTS_BITNR = 0,
+	QCOW_COMPAT_LAZY_REFCOUNTS       = 1 << QCOW_COMPAT_LAZY_REFCOUNTS_BITNR,
+
+	QCOW_COMPAT_FEAT_MASK            = QCOW_COMPAT_LAZY_REFCOUNTS,
+};
+
+/* autoclear feature bits */
+enum {
+	QCOW_AUTOCLEAR_BITMAPS_BITNR       = 0,
+	QCOW_AUTOCLEAR_DATA_FILE_RAW_BITNR = 1,
+	QCOW_AUTOCLEAR_BITMAPS             = 1 << QCOW_AUTOCLEAR_BITMAPS_BITNR,
+	QCOW_AUTOCLEAR_DATA_FILE_RAW       = 1 << QCOW_AUTOCLEAR_DATA_FILE_RAW_BITNR,
+
+	QCOW_AUTOCLEAR_MASK                = QCOW_AUTOCLEAR_BITMAPS |
+						QCOW_AUTOCLEAR_DATA_FILE_RAW,
+};
+
+struct loop_file_fmt_qcow_data {
+	u64 size;
+	int cluster_bits;
+	int cluster_size;
+	int cluster_sectors;
+	int l2_slice_size;
+	int l2_bits;
+	int l2_size;
+	int l1_size;
+	int l1_vm_state_index;
+	int refcount_block_bits;
+	int refcount_block_size;
+	int csize_shift;
+	int csize_mask;
+	u64 cluster_offset_mask;
+	u64 l1_table_offset;
+	u64 *l1_table;
+
+	struct loop_file_fmt_qcow_cache *l2_table_cache;
+	struct loop_file_fmt_qcow_cache *refcount_block_cache;
+
+	u64 *refcount_table;
+	u64 refcount_table_offset;
+	u32 refcount_table_size;
+	u32 max_refcount_table_index; /* Last used entry in refcount_table */
+	u64 free_cluster_index;
+	u64 free_byte_offset;
+
+	u32 crypt_method_header;
+	u64 snapshots_offset;
+	int snapshots_size;
+	unsigned int nb_snapshots;
+
+	u32 nb_bitmaps;
+	u64 bitmap_directory_size;
+	u64 bitmap_directory_offset;
+
+	int qcow_version;
+	bool use_lazy_refcounts;
+	int refcount_order;
+	int refcount_bits;
+	u64 refcount_max;
+
+	u64 incompatible_features;
+	u64 compatible_features;
+	u64 autoclear_features;
+
+	struct z_stream_s *strm;
+
+	/* debugfs entries */
+#ifdef CONFIG_DEBUG_FS
+	struct dentry *dbgfs_dir;
+	struct dentry *dbgfs_file_qcow_header;
+	char dbgfs_file_qcow_header_buf[QCOW_HEADER_BUF_LEN];
+	struct dentry *dbgfs_file_qcow_offset;
+	char dbgfs_file_qcow_offset_buf[QCOW_OFFSET_BUF_LEN];
+	char dbgfs_file_qcow_cluster_buf[QCOW_CLUSTER_BUF_LEN];
+	u64 dbgfs_qcow_offset;
+	struct mutex dbgfs_qcow_offset_mutex;
+#endif
+};
+
+struct loop_file_fmt_qcow_cow_region {
+	/**
+	 * Offset of the COW region in bytes from the start of the first
+	 * cluster touched by the request.
+	 */
+	unsigned offset;
+
+	/** Number of bytes to copy */
+	unsigned nb_bytes;
+};
+
+enum loop_file_fmt_qcow_cluster_type {
+	QCOW_CLUSTER_UNALLOCATED,
+	QCOW_CLUSTER_ZERO_PLAIN,
+	QCOW_CLUSTER_ZERO_ALLOC,
+	QCOW_CLUSTER_NORMAL,
+	QCOW_CLUSTER_COMPRESSED,
+};
+
+enum loop_file_fmt_qcow_metadata_overlap {
+	QCOW_OL_MAIN_HEADER_BITNR      = 0,
+	QCOW_OL_ACTIVE_L1_BITNR        = 1,
+	QCOW_OL_ACTIVE_L2_BITNR        = 2,
+	QCOW_OL_REFCOUNT_TABLE_BITNR   = 3,
+	QCOW_OL_REFCOUNT_BLOCK_BITNR   = 4,
+	QCOW_OL_SNAPSHOT_TABLE_BITNR   = 5,
+	QCOW_OL_INACTIVE_L1_BITNR      = 6,
+	QCOW_OL_INACTIVE_L2_BITNR      = 7,
+	QCOW_OL_BITMAP_DIRECTORY_BITNR = 8,
+
+	QCOW_OL_MAX_BITNR              = 9,
+
+	QCOW_OL_NONE             = 0,
+	QCOW_OL_MAIN_HEADER      = (1 << QCOW_OL_MAIN_HEADER_BITNR),
+	QCOW_OL_ACTIVE_L1        = (1 << QCOW_OL_ACTIVE_L1_BITNR),
+	QCOW_OL_ACTIVE_L2        = (1 << QCOW_OL_ACTIVE_L2_BITNR),
+	QCOW_OL_REFCOUNT_TABLE   = (1 << QCOW_OL_REFCOUNT_TABLE_BITNR),
+	QCOW_OL_REFCOUNT_BLOCK   = (1 << QCOW_OL_REFCOUNT_BLOCK_BITNR),
+	QCOW_OL_SNAPSHOT_TABLE   = (1 << QCOW_OL_SNAPSHOT_TABLE_BITNR),
+	QCOW_OL_INACTIVE_L1      = (1 << QCOW_OL_INACTIVE_L1_BITNR),
+	/* NOTE: Checking overlaps with inactive L2 tables will result in bdrv
+	 * reads. */
+	QCOW_OL_INACTIVE_L2      = (1 << QCOW_OL_INACTIVE_L2_BITNR),
+	QCOW_OL_BITMAP_DIRECTORY = (1 << QCOW_OL_BITMAP_DIRECTORY_BITNR),
+};
+
+/* Perform all overlap checks which can be done in constant time */
+#define QCOW_OL_CONSTANT \
+	(QCOW_OL_MAIN_HEADER | QCOW_OL_ACTIVE_L1 | QCOW_OL_REFCOUNT_TABLE | \
+		QCOW_OL_SNAPSHOT_TABLE | QCOW_OL_BITMAP_DIRECTORY)
+
+/* Perform all overlap checks which don't require disk access */
+#define QCOW_OL_CACHED \
+	(QCOW_OL_CONSTANT | QCOW_OL_ACTIVE_L2 | QCOW_OL_REFCOUNT_BLOCK | \
+		QCOW_OL_INACTIVE_L1)
+
+/* Perform all overlap checks */
+#define QCOW_OL_ALL \
+	(QCOW_OL_CACHED | QCOW_OL_INACTIVE_L2)
+
+#define L1E_OFFSET_MASK 0x00fffffffffffe00ULL
+#define L2E_OFFSET_MASK 0x00fffffffffffe00ULL
+#define L2E_COMPRESSED_OFFSET_SIZE_MASK 0x3fffffffffffffffULL
+
+#define REFT_OFFSET_MASK 0xfffffffffffffe00ULL
+
+#define INV_OFFSET (-1ULL)
+
+static inline bool loop_file_fmt_qcow_has_data_file(
+	struct loop_file_fmt *lo_fmt)
+{
+	/* At the moment, there is no support for copy on write! */
+	return false;
+}
+
+static inline bool loop_file_fmt_qcow_data_file_is_raw(
+	struct loop_file_fmt *lo_fmt)
+{
+	struct loop_file_fmt_qcow_data *qcow_data = lo_fmt->private_data;
+	return !!(qcow_data->autoclear_features &
+		QCOW_AUTOCLEAR_DATA_FILE_RAW);
+}
+
+static inline s64 loop_file_fmt_qcow_start_of_cluster(
+	struct loop_file_fmt_qcow_data *qcow_data, s64 offset)
+{
+	return offset & ~(qcow_data->cluster_size - 1);
+}
+
+static inline s64 loop_file_fmt_qcow_offset_into_cluster(
+	struct loop_file_fmt_qcow_data *qcow_data, s64 offset)
+{
+	return offset & (qcow_data->cluster_size - 1);
+}
+
+static inline s64 loop_file_fmt_qcow_size_to_clusters(
+	struct loop_file_fmt_qcow_data *qcow_data, u64 size)
+{
+	return (size + (qcow_data->cluster_size - 1)) >>
+		qcow_data->cluster_bits;
+}
+
+static inline s64 loop_file_fmt_qcow_size_to_l1(
+	struct loop_file_fmt_qcow_data *qcow_data, s64 size)
+{
+	int shift = qcow_data->cluster_bits + qcow_data->l2_bits;
+	return (size + (1ULL << shift) - 1) >> shift;
+}
+
+static inline int loop_file_fmt_qcow_offset_to_l1_index(
+	struct loop_file_fmt_qcow_data *qcow_data, u64 offset)
+{
+	return offset >> (qcow_data->l2_bits + qcow_data->cluster_bits);
+}
+
+static inline int loop_file_fmt_qcow_offset_to_l2_index(
+	struct loop_file_fmt_qcow_data *qcow_data, s64 offset)
+{
+	return (offset >> qcow_data->cluster_bits) & (qcow_data->l2_size - 1);
+}
+
+static inline int loop_file_fmt_qcow_offset_to_l2_slice_index(
+	struct loop_file_fmt_qcow_data *qcow_data, s64 offset)
+{
+	return (offset >> qcow_data->cluster_bits) &
+		(qcow_data->l2_slice_size - 1);
+}
+
+static inline s64 loop_file_fmt_qcow_vm_state_offset(
+	struct loop_file_fmt_qcow_data *qcow_data)
+{
+	return (s64)qcow_data->l1_vm_state_index <<
+		(qcow_data->cluster_bits + qcow_data->l2_bits);
+}
+
+static inline enum loop_file_fmt_qcow_cluster_type
+loop_file_fmt_qcow_get_cluster_type(struct loop_file_fmt *lo_fmt, u64 l2_entry)
+{
+	if (l2_entry & QCOW_OFLAG_COMPRESSED) {
+		return QCOW_CLUSTER_COMPRESSED;
+	} else if (l2_entry & QCOW_OFLAG_ZERO) {
+		if (l2_entry & L2E_OFFSET_MASK) {
+			return QCOW_CLUSTER_ZERO_ALLOC;
+		}
+		return QCOW_CLUSTER_ZERO_PLAIN;
+	} else if (!(l2_entry & L2E_OFFSET_MASK)) {
+		/* Offset 0 generally means unallocated, but it is ambiguous
+		 * with external data files because 0 is a valid offset there.
+		 * However, all clusters in external data files always have
+		 * refcount 1, so we can rely on QCOW_OFLAG_COPIED to
+		 * disambiguate. */
+		if (loop_file_fmt_qcow_has_data_file(lo_fmt) &&
+			(l2_entry & QCOW_OFLAG_COPIED)) {
+			return QCOW_CLUSTER_NORMAL;
+		} else {
+			return QCOW_CLUSTER_UNALLOCATED;
+		}
+	} else {
+		return QCOW_CLUSTER_NORMAL;
+	}
+}
+
+#endif
diff --git a/loop_file_fmt_raw.c b/loop_file_fmt_raw.c
new file mode 100644
index 0000000..134a794
--- /dev/null
+++ b/loop_file_fmt_raw.c
@@ -0,0 +1,450 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * loop_file_fmt_raw.c
+ *
+ * RAW file format driver for the loop device module.
+ *
+ * Copyright (C) 2019 Manuel Bentele <development@manuel-bentele.de>
+ */
+
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/init.h>
+#include <linux/blkdev.h>
+#include <linux/compiler.h>
+#include <linux/blk-cgroup.h>
+#include <linux/fs.h>
+#include <linux/falloc.h>
+#include <linux/printk.h>
+#include <linux/sched.h>
+#include <linux/types.h>
+#include <linux/uio.h>
+
+#include "loop_file_fmt.h"
+
+static inline loff_t __raw_file_fmt_rq_get_pos(struct loop_file_fmt *lo_fmt,
+					       struct request *rq)
+{
+	struct loop_device *lo = loop_file_fmt_get_lo(lo_fmt);
+	return ((loff_t) blk_rq_pos(rq) << 9) + lo->lo_offset;
+}
+
+/* transfer function for DEPRECATED cryptoloop support */
+static inline int __raw_file_fmt_do_transfer(struct loop_file_fmt *lo_fmt,
+					     int cmd,
+					     struct page *rpage,
+					     unsigned roffs,
+					     struct page *lpage,
+					     unsigned loffs,
+					     int size,
+					     sector_t rblock)
+{
+	struct loop_device *lo = loop_file_fmt_get_lo(lo_fmt);
+	int ret;
+
+	ret = lo->transfer(lo, cmd, rpage, roffs, lpage, loffs, size, rblock);
+	if (likely(!ret))
+		return 0;
+
+	printk_ratelimited(KERN_ERR
+		"loop: Transfer error at byte offset %llu, length %i.\n",
+		(unsigned long long)rblock << 9, size);
+	return ret;
+}
+
+static int raw_file_fmt_read_transfer(struct loop_file_fmt *lo_fmt,
+				      struct request *rq)
+{
+	struct bio_vec bvec, b;
+	struct req_iterator iter;
+	struct iov_iter i;
+	struct page *page;
+	struct loop_device *lo;
+	ssize_t len;
+	int ret = 0;
+	loff_t pos;
+
+	page = alloc_page(GFP_NOIO);
+	if (unlikely(!page))
+		return -ENOMEM;
+
+	lo = loop_file_fmt_get_lo(lo_fmt);
+	pos = __raw_file_fmt_rq_get_pos(lo_fmt, rq);
+
+	rq_for_each_segment(bvec, rq, iter) {
+		loff_t offset = pos;
+
+		b.bv_page = page;
+		b.bv_offset = 0;
+		b.bv_len = bvec.bv_len;
+
+		iov_iter_bvec(&i, ITER_BVEC, &b, 1, b.bv_len);
+		len = vfs_iter_read(lo->lo_backing_file, &i, &pos, 0);
+		if (len < 0) {
+			ret = len;
+			goto out_free_page;
+		}
+
+		ret = __raw_file_fmt_do_transfer(lo_fmt, READ, page, 0,
+			bvec.bv_page, bvec.bv_offset, len, offset >> 9);
+		if (ret)
+			goto out_free_page;
+
+		flush_dcache_page(bvec.bv_page);
+
+		if (len != bvec.bv_len) {
+			struct bio *bio;
+
+			__rq_for_each_bio(bio, rq)
+				zero_fill_bio(bio);
+			break;
+		}
+	}
+
+	ret = 0;
+out_free_page:
+	__free_page(page);
+	return ret;
+}
+
+static int raw_file_fmt_read(struct loop_file_fmt *lo_fmt,
+			     struct request *rq)
+{
+	struct bio_vec bvec;
+	struct req_iterator iter;
+	struct iov_iter i;
+	struct loop_device *lo;
+	ssize_t len;
+	loff_t pos;
+
+	lo = loop_file_fmt_get_lo(lo_fmt);
+
+	if (lo->transfer)
+		return raw_file_fmt_read_transfer(lo_fmt, rq);
+
+	pos = __raw_file_fmt_rq_get_pos(lo_fmt, rq);
+
+	rq_for_each_segment(bvec, rq, iter) {
+		iov_iter_bvec(&i, ITER_BVEC, &bvec, 1, bvec.bv_len);
+		len = vfs_iter_read(lo->lo_backing_file, &i, &pos, 0);
+		if (len < 0)
+			return len;
+
+		flush_dcache_page(bvec.bv_page);
+
+		if (len != bvec.bv_len) {
+			struct bio *bio;
+
+			__rq_for_each_bio(bio, rq)
+				zero_fill_bio(bio);
+			break;
+		}
+		cond_resched();
+	}
+
+	return 0;
+}
+
+static void __raw_file_fmt_rw_aio_do_completion(struct loop_cmd *cmd)
+{
+	struct request *rq = blk_mq_rq_from_pdu(cmd);
+
+	if (!atomic_dec_and_test(&cmd->ref))
+		return;
+	kfree(cmd->bvec);
+	cmd->bvec = NULL;
+	blk_mq_complete_request(rq);
+}
+
+static void __raw_file_fmt_rw_aio_complete(struct kiocb *iocb, long ret, long ret2)
+{
+	struct loop_cmd *cmd = container_of(iocb, struct loop_cmd, iocb);
+
+	if (cmd->css)
+		css_put(cmd->css);
+	cmd->ret = ret;
+	__raw_file_fmt_rw_aio_do_completion(cmd);
+}
+
+static int __raw_file_fmt_rw_aio(struct loop_file_fmt *lo_fmt,
+				 struct request *rq,
+				 bool rw)
+{
+	struct iov_iter iter;
+	struct bio_vec *bvec;
+	struct bio *bio = rq->bio;
+	struct file *file;
+	struct loop_device *lo;
+	struct loop_cmd *cmd;
+	unsigned int offset;
+	int segments = 0;
+	int ret;
+	loff_t pos;
+
+	lo = loop_file_fmt_get_lo(lo_fmt);
+	file = lo->lo_backing_file;
+	cmd = blk_mq_rq_to_pdu(rq);
+	pos = __raw_file_fmt_rq_get_pos(lo_fmt, rq);
+
+	if (rq->bio != rq->biotail) {
+		struct req_iterator iter;
+		struct bio_vec tmp;
+
+		__rq_for_each_bio(bio, rq)
+			segments += bio_segments(bio);
+		bvec = kmalloc_array(segments, sizeof(struct bio_vec),
+				     GFP_NOIO);
+		if (!bvec)
+			return -EIO;
+		cmd->bvec = bvec;
+
+		/*
+		 * The bios of the request may be started from the middle of
+		 * the 'bvec' because of bio splitting, so we can't directly
+		 * copy bio->bi_iov_vec to new bvec. The rq_for_each_segment
+		 * API will take care of all details for us.
+		 */
+		rq_for_each_segment(tmp, rq, iter) {
+			*bvec = tmp;
+			bvec++;
+		}
+		bvec = cmd->bvec;
+		offset = 0;
+	} else {
+		/*
+		 * Same here, this bio may be started from the middle of the
+		 * 'bvec' because of bio splitting, so offset from the bvec
+		 * must be passed to iov iterator
+		 */
+		offset = bio->bi_iter.bi_bvec_done;
+		bvec = __bvec_iter_bvec(bio->bi_io_vec, bio->bi_iter);
+		segments = bio_segments(bio);
+	}
+	atomic_set(&cmd->ref, 2);
+
+	iov_iter_bvec(&iter, ITER_BVEC | rw, bvec, 
+		      segments, blk_rq_bytes(rq));
+	iter.iov_offset = offset;
+
+	cmd->iocb.ki_pos = pos;
+	cmd->iocb.ki_filp = file;
+	cmd->iocb.ki_complete = __raw_file_fmt_rw_aio_complete;
+	cmd->iocb.ki_flags = IOCB_DIRECT;
+	cmd->iocb.ki_ioprio = IOPRIO_PRIO_VALUE(IOPRIO_CLASS_NONE, 0);
+	if (cmd->css)
+		kthread_associate_blkcg(cmd->css);
+
+	if (rw == WRITE)
+		ret = call_write_iter(file, &cmd->iocb, &iter);
+	else
+		ret = call_read_iter(file, &cmd->iocb, &iter);
+
+	__raw_file_fmt_rw_aio_do_completion(cmd);
+	kthread_associate_blkcg(NULL);
+
+	if (ret != -EIOCBQUEUED)
+		cmd->iocb.ki_complete(&cmd->iocb, ret, 0);
+	return 0;
+}
+
+static int raw_file_fmt_read_aio(struct loop_file_fmt *lo_fmt,
+				 struct request *rq)
+{
+	return __raw_file_fmt_rw_aio(lo_fmt, rq, READ);
+}
+
+static int __raw_file_fmt_write_bvec(struct file *file,
+				     struct bio_vec *bvec,
+				     loff_t *ppos)
+{
+	struct iov_iter i;
+	ssize_t bw;
+
+	iov_iter_bvec(&i, ITER_BVEC | WRITE, bvec, 1, bvec->bv_len);
+
+	file_start_write(file);
+	bw = vfs_iter_write(file, &i, ppos, 0);
+	file_end_write(file);
+
+	if (likely(bw ==  bvec->bv_len))
+		return 0;
+
+	printk_ratelimited(KERN_ERR
+		"loop_file_fmt_raw: Write error at byte offset %llu, length "
+		"%i.\n", (unsigned long long)*ppos, bvec->bv_len);
+	if (bw >= 0)
+		bw = -EIO;
+	return bw;
+}
+
+static int raw_file_fmt_write_transfer(struct loop_file_fmt *lo_fmt,
+				       struct request *rq)
+{
+	struct bio_vec bvec, b;
+	struct req_iterator iter;
+	struct page *page;
+	struct loop_device *lo;
+	int ret = 0;
+	loff_t pos;
+
+	lo = loop_file_fmt_get_lo(lo_fmt);
+	pos = __raw_file_fmt_rq_get_pos(lo_fmt, rq);
+
+	page = alloc_page(GFP_NOIO);
+	if (unlikely(!page))
+		return -ENOMEM;
+
+	rq_for_each_segment(bvec, rq, iter) {
+		ret = __raw_file_fmt_do_transfer(lo_fmt, WRITE, page, 0,
+			bvec.bv_page, bvec.bv_offset, bvec.bv_len, pos >> 9);
+		if (unlikely(ret))
+			break;
+
+		b.bv_page = page;
+		b.bv_offset = 0;
+		b.bv_len = bvec.bv_len;
+		ret = __raw_file_fmt_write_bvec(lo->lo_backing_file, &b,
+			&pos);
+		if (ret < 0)
+			break;
+	}
+
+	__free_page(page);
+	return ret;
+}
+
+static int raw_file_fmt_write(struct loop_file_fmt *lo_fmt,
+			      struct request *rq)
+{
+	struct bio_vec bvec;
+	struct req_iterator iter;
+	struct loop_device *lo;
+	int ret = 0;
+	loff_t pos;
+
+	lo = loop_file_fmt_get_lo(lo_fmt);
+
+	if (lo->transfer)
+		return raw_file_fmt_write_transfer(lo_fmt, rq);
+
+	pos = __raw_file_fmt_rq_get_pos(lo_fmt, rq);
+
+	rq_for_each_segment(bvec, rq, iter) {
+		ret = __raw_file_fmt_write_bvec(lo->lo_backing_file, &bvec,
+			&pos);
+		if (ret < 0)
+			break;
+		cond_resched();
+	}
+
+	return ret;
+}
+
+static int raw_file_fmt_write_aio(struct loop_file_fmt *lo_fmt,
+				  struct request *rq)
+{
+	return __raw_file_fmt_rw_aio(lo_fmt, rq, WRITE);
+}
+
+static int raw_file_fmt_discard(struct loop_file_fmt *lo_fmt,
+				struct request *rq)
+{
+	loff_t pos = __raw_file_fmt_rq_get_pos(lo_fmt, rq);
+	struct loop_device *lo = loop_file_fmt_get_lo(lo_fmt);
+
+	/*
+	 * We use punch hole to reclaim the free space used by the
+	 * image a.k.a. discard. However we do not support discard if
+	 * encryption is enabled, because it may give an attacker
+	 * useful information.
+	 */
+	struct file *file = lo->lo_backing_file;
+	int mode = FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE;
+	int ret;
+
+	if ((!file->f_op->fallocate) || lo->lo_encrypt_key_size) {
+		ret = -EOPNOTSUPP;
+		goto out;
+	}
+
+	ret = file->f_op->fallocate(file, mode, pos, blk_rq_bytes(rq));
+	if (unlikely(ret && ret != -EINVAL && ret != -EOPNOTSUPP))
+		ret = -EIO;
+ out:
+	return ret;
+}
+
+static int raw_file_fmt_flush(struct loop_file_fmt *lo_fmt)
+{
+	struct loop_device *lo = loop_file_fmt_get_lo(lo_fmt);
+	struct file *file = lo->lo_backing_file;
+	int ret = vfs_fsync(file, 0);
+	if (unlikely(ret && ret != -EINVAL))
+		ret = -EIO;
+
+	return ret;
+}
+
+static loff_t raw_file_fmt_sector_size(struct loop_file_fmt *lo_fmt)
+{
+	struct loop_device *lo = loop_file_fmt_get_lo(lo_fmt);
+	loff_t loopsize;
+
+	/* Compute loopsize in bytes */
+	loopsize = i_size_read(lo->lo_backing_file->f_mapping->host);
+	if (lo->lo_offset > 0)
+		loopsize -= lo->lo_offset;
+	/* offset is beyond i_size, weird but possible */
+	if (loopsize < 0)
+		return 0;
+
+	if (lo->lo_sizelimit > 0 && lo->lo_sizelimit < loopsize)
+		loopsize = lo->lo_sizelimit;
+
+	/*
+	 * Unfortunately, if we want to do I/O on the device,
+	 * the number of 512-byte sectors has to fit into a sector_t.
+	 */
+	return loopsize >> 9;
+}
+
+static struct loop_file_fmt_ops raw_file_fmt_ops = {
+	.init = NULL,
+	.exit = NULL,
+	.read = raw_file_fmt_read,
+	.write = raw_file_fmt_write,
+	.read_aio = raw_file_fmt_read_aio,
+	.write_aio = raw_file_fmt_write_aio,
+	.discard = raw_file_fmt_discard,
+	.flush = raw_file_fmt_flush,
+	.sector_size = raw_file_fmt_sector_size
+};
+
+static struct loop_file_fmt_driver raw_file_fmt_driver = {
+	.name = "RAW",
+	.file_fmt_type = LO_FILE_FMT_RAW,
+	.ops = &raw_file_fmt_ops,
+	.owner = THIS_MODULE
+};
+
+static int __init loop_file_fmt_raw_init(void)
+{
+	printk(KERN_INFO "loop_file_fmt_raw: init loop device RAW file format "
+		"driver");
+	return loop_file_fmt_register_driver(&raw_file_fmt_driver);
+}
+
+static void __exit loop_file_fmt_raw_exit(void)
+{
+	printk(KERN_INFO "loop_file_fmt_raw: exit loop device RAW file format "
+		"driver");
+	loop_file_fmt_unregister_driver(&raw_file_fmt_driver);
+}
+
+module_init(loop_file_fmt_raw_init);
+module_exit(loop_file_fmt_raw_exit);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Manuel Bentele <development@manuel-bentele.de>");
+MODULE_DESCRIPTION("Loop device RAW file format driver");
+MODULE_SOFTDEP("pre: loop");
diff --git a/loop_main.c b/loop_main.c
new file mode 100644
index 0000000..7c1bb19
--- /dev/null
+++ b/loop_main.c
@@ -0,0 +1,2173 @@
+/*
+ *  loop_main.c
+ *
+ *  Written by Theodore Ts'o, 3/29/93
+ *
+ * Copyright 1993 by Theodore Ts'o.  Redistribution of this file is
+ * permitted under the GNU General Public License.
+ *
+ * DES encryption plus some minor changes by Werner Almesberger, 30-MAY-1993
+ * more DES encryption plus IDEA encryption by Nicholas J. Leon, June 20, 1996
+ *
+ * Modularized and updated for 1.1.16 kernel - Mitch Dsouza 28th May 1994
+ * Adapted for 1.3.59 kernel - Andries Brouwer, 1 Feb 1996
+ *
+ * Fixed do_loop_request() re-entrancy - Vincent.Renardias@waw.com Mar 20, 1997
+ *
+ * Added devfs support - Richard Gooch <rgooch@atnf.csiro.au> 16-Jan-1998
+ *
+ * Handle sparse backing files correctly - Kenn Humborg, Jun 28, 1998
+ *
+ * Loadable modules and other fixes by AK, 1998
+ *
+ * Make real block number available to downstream transfer functions, enables
+ * CBC (and relatives) mode encryption requiring unique IVs per data block.
+ * Reed H. Petty, rhp@draper.net
+ *
+ * Maximum number of loop devices now dynamic via max_loop module parameter.
+ * Russell Kroll <rkroll@exploits.org> 19990701
+ *
+ * Maximum number of loop devices when compiled-in now selectable by passing
+ * max_loop=<1-255> to the kernel on boot.
+ * Erik I. Bolsø, <eriki@himolde.no>, Oct 31, 1999
+ *
+ * Completely rewrite request handling to be make_request_fn style and
+ * non blocking, pushing work to a helper thread. Lots of fixes from
+ * Al Viro too.
+ * Jens Axboe <axboe@suse.de>, Nov 2000
+ *
+ * Support up to 256 loop devices
+ * Heinz Mauelshagen <mge@sistina.com>, Feb 2002
+ *
+ * Support for falling back on the write file operation when the address space
+ * operations write_begin is not available on the backing filesystem.
+ * Anton Altaparmakov, 16 Feb 2005
+ *
+ * Support for using file formats.
+ * Manuel Bentele <development@manuel-bentele.de>, 2019
+ *
+ * Still To Fix:
+ * - Advisory locking is ignored here.
+ * - Should use an own CAP_* category instead of CAP_SYS_ADMIN
+ *
+ */
+
+#include <linux/module.h>
+#include <linux/moduleparam.h>
+#include <linux/sched.h>
+#include <linux/fs.h>
+#include <linux/file.h>
+#include <linux/stat.h>
+#include <linux/errno.h>
+#include <linux/major.h>
+#include <linux/wait.h>
+#include <linux/blkdev.h>
+#include <linux/blkpg.h>
+#include <linux/init.h>
+#include <linux/swap.h>
+#include <linux/slab.h>
+#include <linux/compat.h>
+#include <linux/suspend.h>
+#include <linux/freezer.h>
+#include <linux/mutex.h>
+#include <linux/writeback.h>
+#include <linux/completion.h>
+#include <linux/highmem.h>
+#include <linux/kthread.h>
+#include <linux/splice.h>
+#include <linux/sysfs.h>
+#include <linux/miscdevice.h>
+#include <linux/falloc.h>
+#include <linux/uio.h>
+#include <linux/ioprio.h>
+
+#include "loop_file_fmt.h"
+#include "loop_main.h"
+
+#include <linux/uaccess.h>
+
+static DEFINE_IDR(loop_index_idr);
+static DEFINE_MUTEX(loop_ctl_mutex);
+
+static int max_part;
+static int part_shift;
+
+static int transfer_xor(struct loop_device *lo, int cmd,
+			struct page *raw_page, unsigned raw_off,
+			struct page *loop_page, unsigned loop_off,
+			int size, sector_t real_block)
+{
+	char *raw_buf = kmap_atomic(raw_page) + raw_off;
+	char *loop_buf = kmap_atomic(loop_page) + loop_off;
+	char *in, *out, *key;
+	int i, keysize;
+
+	if (cmd == READ) {
+		in = raw_buf;
+		out = loop_buf;
+	} else {
+		in = loop_buf;
+		out = raw_buf;
+	}
+
+	key = lo->lo_encrypt_key;
+	keysize = lo->lo_encrypt_key_size;
+	for (i = 0; i < size; i++)
+		*out++ = *in++ ^ key[(i & 511) % keysize];
+
+	kunmap_atomic(loop_buf);
+	kunmap_atomic(raw_buf);
+	cond_resched();
+	return 0;
+}
+
+static int xor_init(struct loop_device *lo, const struct loop_info64 *info)
+{
+	if (unlikely(info->lo_encrypt_key_size <= 0))
+		return -EINVAL;
+	return 0;
+}
+
+static struct loop_func_table none_funcs = {
+	.number = LO_CRYPT_NONE,
+}; 
+
+static struct loop_func_table xor_funcs = {
+	.number = LO_CRYPT_XOR,
+	.transfer = transfer_xor,
+	.init = xor_init
+}; 
+
+/* xfer_funcs[0] is special - its release function is never called */
+static struct loop_func_table *xfer_funcs[MAX_LO_CRYPT] = {
+	&none_funcs,
+	&xor_funcs
+};
+
+static loff_t get_size(loff_t offset, loff_t sizelimit, struct file *file)
+{
+	loff_t loopsize;
+
+	/* Compute loopsize in bytes */
+	loopsize = i_size_read(file->f_mapping->host);
+	if (offset > 0)
+		loopsize -= offset;
+	/* offset is beyond i_size, weird but possible */
+	if (loopsize < 0)
+		return 0;
+
+	if (sizelimit > 0 && sizelimit < loopsize)
+		loopsize = sizelimit;
+	/*
+	 * Unfortunately, if we want to do I/O on the device,
+	 * the number of 512-byte sectors has to fit into a sector_t.
+	 */
+	return loopsize >> 9;
+}
+
+static loff_t get_loop_size(struct loop_device *lo, struct file *file)
+{
+	return get_size(lo->lo_offset, lo->lo_sizelimit, file);
+}
+
+static void __loop_update_dio(struct loop_device *lo, bool dio)
+{
+	struct file *file = lo->lo_backing_file;
+	struct address_space *mapping = file->f_mapping;
+	struct inode *inode = mapping->host;
+	unsigned short sb_bsize = 0;
+	unsigned dio_align = 0;
+	bool use_dio;
+
+	if (inode->i_sb->s_bdev) {
+		sb_bsize = bdev_logical_block_size(inode->i_sb->s_bdev);
+		dio_align = sb_bsize - 1;
+	}
+
+	/*
+	 * We support direct I/O only if lo_offset is aligned with the
+	 * logical I/O size of backing device, and the logical block
+	 * size of loop is bigger than the backing device's and the loop
+	 * needn't transform transfer.
+	 *
+	 * TODO: the above condition may be loosed in the future, and
+	 * direct I/O may be switched runtime at that time because most
+	 * of requests in sane applications should be PAGE_SIZE aligned
+	 */
+	if (dio) {
+		if (queue_logical_block_size(lo->lo_queue) >= sb_bsize &&
+				!(lo->lo_offset & dio_align) &&
+				mapping->a_ops->direct_IO &&
+				!lo->transfer)
+			use_dio = true;
+		else
+			use_dio = false;
+	} else {
+		use_dio = false;
+	}
+
+	if (lo->use_dio == use_dio)
+		return;
+
+	/* flush dirty pages before changing direct IO */
+	loop_file_fmt_flush(lo->lo_fmt);
+
+	/*
+	 * The flag of LO_FLAGS_DIRECT_IO is handled similarly with
+	 * LO_FLAGS_READ_ONLY, both are set from kernel, and losetup
+	 * will get updated by ioctl(LOOP_GET_STATUS)
+	 */
+	blk_mq_freeze_queue(lo->lo_queue);
+	lo->use_dio = use_dio;
+	if (use_dio) {
+		blk_queue_flag_clear(QUEUE_FLAG_NOMERGES, lo->lo_queue);
+		lo->lo_flags |= LO_FLAGS_DIRECT_IO;
+	} else {
+		blk_queue_flag_set(QUEUE_FLAG_NOMERGES, lo->lo_queue);
+		lo->lo_flags &= ~LO_FLAGS_DIRECT_IO;
+	}
+	blk_mq_unfreeze_queue(lo->lo_queue);
+}
+
+static int
+figure_loop_size(struct loop_device *lo, loff_t offset, loff_t sizelimit)
+{
+	loff_t size = loop_file_fmt_sector_size(lo->lo_fmt);
+	sector_t x = (sector_t)size;
+	struct block_device *bdev = lo->lo_device;
+
+	if (unlikely((loff_t)x != size))
+		return -EFBIG;
+	if (lo->lo_offset != offset)
+		lo->lo_offset = offset;
+	if (lo->lo_sizelimit != sizelimit)
+		lo->lo_sizelimit = sizelimit;
+
+	set_capacity(lo->lo_disk, x);
+	bd_set_size(bdev, (loff_t)get_capacity(bdev->bd_disk) << 9);
+	/* let user-space know about the new size */
+	kobject_uevent(&disk_to_dev(bdev->bd_disk)->kobj, KOBJ_CHANGE);
+	return 0;
+}
+
+static void lo_complete_rq(struct request *rq)
+{
+	struct loop_cmd *cmd = blk_mq_rq_to_pdu(rq);
+	blk_status_t ret = BLK_STS_OK;
+
+	if (!cmd->use_aio || cmd->ret < 0 || cmd->ret == blk_rq_bytes(rq) ||
+	    req_op(rq) != REQ_OP_READ) {
+		if (cmd->ret < 0)
+			ret = BLK_STS_IOERR;
+		goto end_io;
+	}
+
+	/*
+	 * Short READ - if we got some data, advance our request and
+	 * retry it. If we got no data, end the rest with EIO.
+	 */
+	if (cmd->ret) {
+		blk_update_request(rq, BLK_STS_OK, cmd->ret);
+		cmd->ret = 0;
+		blk_mq_requeue_request(rq, true);
+	} else {
+		if (cmd->use_aio) {
+			struct bio *bio = rq->bio;
+
+			while (bio) {
+				zero_fill_bio(bio);
+				bio = bio->bi_next;
+			}
+		}
+		ret = BLK_STS_IOERR;
+end_io:
+		blk_mq_end_request(rq, ret);
+	}
+}
+
+static int do_req_filebacked(struct loop_device *lo, struct request *rq)
+{
+	struct loop_cmd *cmd = blk_mq_rq_to_pdu(rq);
+
+	switch (req_op(rq)) {
+	case REQ_OP_FLUSH:
+		return loop_file_fmt_flush(lo->lo_fmt);
+	case REQ_OP_DISCARD:
+	case REQ_OP_WRITE_ZEROES:
+		return loop_file_fmt_discard(lo->lo_fmt, rq);
+	case REQ_OP_WRITE:
+		if (cmd->use_aio)
+			return loop_file_fmt_write_aio(lo->lo_fmt, rq);
+		else
+			return loop_file_fmt_write(lo->lo_fmt, rq);
+	case REQ_OP_READ:
+		if (cmd->use_aio)
+			return loop_file_fmt_read_aio(lo->lo_fmt, rq);
+		else
+			return loop_file_fmt_read(lo->lo_fmt, rq);
+	default:
+		WARN_ON_ONCE(1);
+		return -EIO;
+		break;
+	}
+}
+
+static inline void loop_update_dio(struct loop_device *lo)
+{
+	__loop_update_dio(lo, io_is_direct(lo->lo_backing_file) |
+			lo->use_dio);
+}
+
+static void loop_reread_partitions(struct loop_device *lo,
+				   struct block_device *bdev)
+{
+	int rc;
+
+	rc = blkdev_reread_part(bdev);
+	if (rc)
+		pr_warn("%s: partition scan of loop%d (%s) failed (rc=%d)\n",
+			__func__, lo->lo_number, lo->lo_file_name, rc);
+}
+
+static inline int is_loop_device(struct file *file)
+{
+	struct inode *i = file->f_mapping->host;
+
+	return i && S_ISBLK(i->i_mode) && MAJOR(i->i_rdev) == LOOP_MAJOR;
+}
+
+static int loop_validate_file(struct file *file, struct block_device *bdev)
+{
+	struct inode	*inode = file->f_mapping->host;
+	struct file	*f = file;
+
+	/* Avoid recursion */
+	while (is_loop_device(f)) {
+		struct loop_device *l;
+
+		if (f->f_mapping->host->i_bdev == bdev)
+			return -EBADF;
+
+		l = f->f_mapping->host->i_bdev->bd_disk->private_data;
+		if (l->lo_state != Lo_bound) {
+			return -EINVAL;
+		}
+		f = l->lo_backing_file;
+	}
+	if (!S_ISREG(inode->i_mode) && !S_ISBLK(inode->i_mode))
+		return -EINVAL;
+	return 0;
+}
+
+/*
+ * loop_change_fd switched the backing store of a loopback device to
+ * a new file. This is useful for operating system installers to free up
+ * the original file and in High Availability environments to switch to
+ * an alternative location for the content in case of server meltdown.
+ * This can only work if the loop device is used read-only, and if the
+ * new backing store is the same size and type as the old backing store.
+ */
+static int loop_change_fd(struct loop_device *lo, struct block_device *bdev,
+			  unsigned int arg)
+{
+	struct file	*file = NULL, *old_file;
+	int		error;
+	bool		partscan;
+
+	error = mutex_lock_killable(&loop_ctl_mutex);
+	if (error)
+		return error;
+	error = -ENXIO;
+	if (lo->lo_state != Lo_bound)
+		goto out_err;
+
+	/* the loop device has to be read-only */
+	error = -EINVAL;
+	if (!(lo->lo_flags & LO_FLAGS_READ_ONLY))
+		goto out_err;
+
+	error = -EBADF;
+	file = fget(arg);
+	if (!file)
+		goto out_err;
+
+	error = loop_validate_file(file, bdev);
+	if (error)
+		goto out_err;
+
+	old_file = lo->lo_backing_file;
+
+	error = -EINVAL;
+
+	/* size of the new backing store needs to be the same */
+	if (get_loop_size(lo, file) != get_loop_size(lo, old_file))
+		goto out_err;
+
+	/* and ... switch */
+	blk_mq_freeze_queue(lo->lo_queue);
+	mapping_set_gfp_mask(old_file->f_mapping, lo->old_gfp_mask);
+	lo->lo_backing_file = file;
+	lo->old_gfp_mask = mapping_gfp_mask(file->f_mapping);
+	mapping_set_gfp_mask(file->f_mapping,
+			     lo->old_gfp_mask & ~(__GFP_IO|__GFP_FS));
+	loop_update_dio(lo);
+	blk_mq_unfreeze_queue(lo->lo_queue);
+	partscan = lo->lo_flags & LO_FLAGS_PARTSCAN;
+	mutex_unlock(&loop_ctl_mutex);
+	/*
+	 * We must drop file reference outside of loop_ctl_mutex as dropping
+	 * the file ref can take bd_mutex which creates circular locking
+	 * dependency.
+	 */
+	fput(old_file);
+	if (partscan)
+		loop_reread_partitions(lo, bdev);
+	return 0;
+
+out_err:
+	mutex_unlock(&loop_ctl_mutex);
+	if (file)
+		fput(file);
+	return error;
+}
+
+/* loop sysfs attributes */
+
+static ssize_t loop_attr_show(struct device *dev, char *page,
+			      ssize_t (*callback)(struct loop_device *, char *))
+{
+	struct gendisk *disk = dev_to_disk(dev);
+	struct loop_device *lo = disk->private_data;
+
+	return callback(lo, page);
+}
+
+#define LOOP_ATTR_RO(_name)						\
+static ssize_t loop_attr_##_name##_show(struct loop_device *, char *);	\
+static ssize_t loop_attr_do_show_##_name(struct device *d,		\
+				struct device_attribute *attr, char *b)	\
+{									\
+	return loop_attr_show(d, b, loop_attr_##_name##_show);		\
+}									\
+static struct device_attribute loop_attr_##_name =			\
+	__ATTR(_name, 0444, loop_attr_do_show_##_name, NULL);
+
+static ssize_t loop_attr_backing_file_show(struct loop_device *lo, char *buf)
+{
+	ssize_t ret;
+	char *p = NULL;
+
+	spin_lock_irq(&lo->lo_lock);
+	if (lo->lo_backing_file)
+		p = file_path(lo->lo_backing_file, buf, PAGE_SIZE - 1);
+	spin_unlock_irq(&lo->lo_lock);
+
+	if (IS_ERR_OR_NULL(p))
+		ret = PTR_ERR(p);
+	else {
+		ret = strlen(p);
+		memmove(buf, p, ret);
+		buf[ret++] = '\n';
+		buf[ret] = 0;
+	}
+
+	return ret;
+}
+
+static ssize_t __print_file_fmt_type(__u32 file_fmt_type, char* buf) {
+	switch(file_fmt_type) {
+	case LO_FILE_FMT_RAW:
+		sprintf(buf, "%s\n", "RAW");
+		break;
+	case LO_FILE_FMT_QCOW:
+		sprintf(buf, "%s\n", "QCOW");
+		break;
+	case LO_FILE_FMT_VDI:
+		sprintf(buf, "%s\n", "VDI");
+		break;
+	case LO_FILE_FMT_VMDK:
+		sprintf(buf, "%s\n", "VMDK");
+		break;
+	default:
+		sprintf(buf, "%s\n", "ERROR: Unsupported loop file format!");
+		break;
+	}
+
+	return strlen(buf);
+}
+
+static ssize_t loop_attr_file_fmt_type_show(struct loop_device *lo, char *buf)
+{
+	return __print_file_fmt_type(lo->lo_fmt->file_fmt_type, buf);
+}
+
+static ssize_t loop_attr_offset_show(struct loop_device *lo, char *buf)
+{
+	return sprintf(buf, "%llu\n", (unsigned long long)lo->lo_offset);
+}
+
+static ssize_t loop_attr_sizelimit_show(struct loop_device *lo, char *buf)
+{
+	return sprintf(buf, "%llu\n", (unsigned long long)lo->lo_sizelimit);
+}
+
+static ssize_t loop_attr_autoclear_show(struct loop_device *lo, char *buf)
+{
+	int autoclear = (lo->lo_flags & LO_FLAGS_AUTOCLEAR);
+
+	return sprintf(buf, "%s\n", autoclear ? "1" : "0");
+}
+
+static ssize_t loop_attr_partscan_show(struct loop_device *lo, char *buf)
+{
+	int partscan = (lo->lo_flags & LO_FLAGS_PARTSCAN);
+
+	return sprintf(buf, "%s\n", partscan ? "1" : "0");
+}
+
+static ssize_t loop_attr_dio_show(struct loop_device *lo, char *buf)
+{
+	int dio = (lo->lo_flags & LO_FLAGS_DIRECT_IO);
+
+	return sprintf(buf, "%s\n", dio ? "1" : "0");
+}
+
+LOOP_ATTR_RO(backing_file);
+LOOP_ATTR_RO(file_fmt_type);
+LOOP_ATTR_RO(offset);
+LOOP_ATTR_RO(sizelimit);
+LOOP_ATTR_RO(autoclear);
+LOOP_ATTR_RO(partscan);
+LOOP_ATTR_RO(dio);
+
+static struct attribute *loop_attrs[] = {
+	&loop_attr_backing_file.attr,
+	&loop_attr_file_fmt_type.attr,
+	&loop_attr_offset.attr,
+	&loop_attr_sizelimit.attr,
+	&loop_attr_autoclear.attr,
+	&loop_attr_partscan.attr,
+	&loop_attr_dio.attr,
+	NULL,
+};
+
+static struct attribute_group loop_attribute_group = {
+	.name = "loop",
+	.attrs= loop_attrs,
+};
+
+static void loop_sysfs_init(struct loop_device *lo)
+{
+	lo->sysfs_inited = !sysfs_create_group(&disk_to_dev(lo->lo_disk)->kobj,
+						&loop_attribute_group);
+}
+
+static void loop_sysfs_exit(struct loop_device *lo)
+{
+	if (lo->sysfs_inited)
+		sysfs_remove_group(&disk_to_dev(lo->lo_disk)->kobj,
+				   &loop_attribute_group);
+}
+
+static void loop_config_discard(struct loop_device *lo)
+{
+	struct file *file = lo->lo_backing_file;
+	struct inode *inode = file->f_mapping->host;
+	struct request_queue *q = lo->lo_queue;
+
+	/*
+	 * We use punch hole to reclaim the free space used by the
+	 * image a.k.a. discard. However we do not support discard if
+	 * encryption is enabled, because it may give an attacker
+	 * useful information.
+	 */
+	if ((!file->f_op->fallocate) ||
+	    lo->lo_encrypt_key_size) {
+		q->limits.discard_granularity = 0;
+		q->limits.discard_alignment = 0;
+		blk_queue_max_discard_sectors(q, 0);
+		blk_queue_max_write_zeroes_sectors(q, 0);
+		blk_queue_flag_clear(QUEUE_FLAG_DISCARD, q);
+		return;
+	}
+
+	q->limits.discard_granularity = inode->i_sb->s_blocksize;
+	q->limits.discard_alignment = 0;
+
+	blk_queue_max_discard_sectors(q, UINT_MAX >> 9);
+	blk_queue_max_write_zeroes_sectors(q, UINT_MAX >> 9);
+	blk_queue_flag_set(QUEUE_FLAG_DISCARD, q);
+}
+
+static void loop_unprepare_queue(struct loop_device *lo)
+{
+	kthread_flush_worker(&lo->worker);
+	kthread_stop(lo->worker_task);
+}
+
+static int loop_kthread_worker_fn(void *worker_ptr)
+{
+	current->flags |= PF_LESS_THROTTLE | PF_MEMALLOC_NOIO;
+	return kthread_worker_fn(worker_ptr);
+}
+
+static int loop_prepare_queue(struct loop_device *lo)
+{
+	kthread_init_worker(&lo->worker);
+	lo->worker_task = kthread_run(loop_kthread_worker_fn,
+			&lo->worker, "loop%d", lo->lo_number);
+	if (IS_ERR(lo->worker_task))
+		return -ENOMEM;
+	set_user_nice(lo->worker_task, MIN_NICE);
+	return 0;
+}
+
+static int loop_set_fd(struct loop_device *lo, fmode_t mode,
+		       struct block_device *bdev, unsigned int arg)
+{
+	struct file	*file;
+	struct inode	*inode;
+	struct address_space *mapping;
+	int		lo_flags = 0;
+	int		error;
+	loff_t		size;
+	bool		partscan;
+
+	/* This is safe, since we have a reference from open(). */
+	__module_get(THIS_MODULE);
+
+	error = -EBADF;
+	file = fget(arg);
+	if (!file)
+		goto out;
+
+	error = mutex_lock_killable(&loop_ctl_mutex);
+	if (error)
+		goto out_putf;
+
+	error = -EBUSY;
+	if (lo->lo_state != Lo_unbound)
+		goto out_unlock;
+
+	error = loop_validate_file(file, bdev);
+	if (error)
+		goto out_unlock;
+
+	mapping = file->f_mapping;
+	inode = mapping->host;
+
+	if (!(file->f_mode & FMODE_WRITE) || !(mode & FMODE_WRITE) ||
+	    !file->f_op->write_iter)
+		lo_flags |= LO_FLAGS_READ_ONLY;
+
+	set_device_ro(bdev, (lo_flags & LO_FLAGS_READ_ONLY) != 0);
+
+	lo->use_dio = false;
+	lo->lo_device = bdev;
+	lo->lo_flags = lo_flags;
+	lo->lo_backing_file = file;
+	lo->transfer = NULL;
+	lo->ioctl = NULL;
+	lo->lo_sizelimit = 0;
+	lo->old_gfp_mask = mapping_gfp_mask(mapping);
+	mapping_set_gfp_mask(mapping, lo->old_gfp_mask & ~(__GFP_IO|__GFP_FS));
+
+	if (!(lo_flags & LO_FLAGS_READ_ONLY) && file->f_op->fsync)
+		blk_queue_write_cache(lo->lo_queue, true, false);
+
+	loop_update_dio(lo);
+
+	error = loop_file_fmt_init(lo->lo_fmt, LO_FILE_FMT_RAW);
+	if (error)
+		goto out_unlock;
+
+	size = loop_file_fmt_sector_size(lo->lo_fmt);
+
+	error = -EFBIG;
+	if ((loff_t)(sector_t)size != size)
+		goto out_unlock;
+	error = loop_prepare_queue(lo);
+	if (error)
+		goto out_unlock;
+
+	set_capacity(lo->lo_disk, size);
+	bd_set_size(bdev, size << 9);
+	loop_sysfs_init(lo);
+	/* let user-space know about the new size */
+	kobject_uevent(&disk_to_dev(bdev->bd_disk)->kobj, KOBJ_CHANGE);
+
+	set_blocksize(bdev, S_ISBLK(inode->i_mode) ?
+		      block_size(inode->i_bdev) : PAGE_SIZE);
+
+	lo->lo_state = Lo_bound;
+	if (part_shift)
+		lo->lo_flags |= LO_FLAGS_PARTSCAN;
+	partscan = lo->lo_flags & LO_FLAGS_PARTSCAN;
+
+	/* Grab the block_device to prevent its destruction after we
+	 * put /dev/loopXX inode. Later in __loop_clr_fd() we bdput(bdev).
+	 */
+	bdgrab(bdev);
+	mutex_unlock(&loop_ctl_mutex);
+	if (partscan)
+		loop_reread_partitions(lo, bdev);
+	return 0;
+
+out_unlock:
+	mutex_unlock(&loop_ctl_mutex);
+out_putf:
+	fput(file);
+out:
+	/* This is safe: open() is still holding a reference. */
+	module_put(THIS_MODULE);
+	return error;
+}
+
+static int
+loop_release_xfer(struct loop_device *lo)
+{
+	int err = 0;
+	struct loop_func_table *xfer = lo->lo_encryption;
+
+	if (xfer) {
+		if (xfer->release)
+			err = xfer->release(lo);
+		lo->transfer = NULL;
+		lo->lo_encryption = NULL;
+		module_put(xfer->owner);
+	}
+	return err;
+}
+
+static int
+loop_init_xfer(struct loop_device *lo, struct loop_func_table *xfer,
+	       const struct loop_info64 *i)
+{
+	int err = 0;
+
+	if (xfer) {
+		struct module *owner = xfer->owner;
+
+		if (!try_module_get(owner))
+			return -EINVAL;
+		if (xfer->init)
+			err = xfer->init(lo, i);
+		if (err)
+			module_put(owner);
+		else
+			lo->lo_encryption = xfer;
+	}
+	return err;
+}
+
+static int __loop_clr_fd(struct loop_device *lo, bool release)
+{
+	struct file *filp = NULL;
+	gfp_t gfp = lo->old_gfp_mask;
+	struct block_device *bdev = lo->lo_device;
+	int err = 0;
+	bool partscan = false;
+	int lo_number;
+
+	mutex_lock(&loop_ctl_mutex);
+	if (WARN_ON_ONCE(lo->lo_state != Lo_rundown)) {
+		err = -ENXIO;
+		goto out_unlock;
+	}
+
+	filp = lo->lo_backing_file;
+	if (filp == NULL) {
+		err = -EINVAL;
+		goto out_unlock;
+	}
+
+	/* freeze request queue during the transition */
+	blk_mq_freeze_queue(lo->lo_queue);
+
+	loop_file_fmt_exit(lo->lo_fmt);
+
+	spin_lock_irq(&lo->lo_lock);
+	lo->lo_backing_file = NULL;
+	spin_unlock_irq(&lo->lo_lock);
+
+	loop_release_xfer(lo);
+	lo->transfer = NULL;
+	lo->ioctl = NULL;
+	lo->lo_device = NULL;
+	lo->lo_encryption = NULL;
+	lo->lo_offset = 0;
+	lo->lo_sizelimit = 0;
+	lo->lo_encrypt_key_size = 0;
+	memset(lo->lo_encrypt_key, 0, LO_KEY_SIZE);
+	memset(lo->lo_crypt_name, 0, LO_NAME_SIZE);
+	memset(lo->lo_file_name, 0, LO_NAME_SIZE);
+	blk_queue_logical_block_size(lo->lo_queue, 512);
+	blk_queue_physical_block_size(lo->lo_queue, 512);
+	blk_queue_io_min(lo->lo_queue, 512);
+	if (bdev) {
+		bdput(bdev);
+		invalidate_bdev(bdev);
+		bdev->bd_inode->i_mapping->wb_err = 0;
+	}
+	set_capacity(lo->lo_disk, 0);
+	loop_sysfs_exit(lo);
+	if (bdev) {
+		bd_set_size(bdev, 0);
+		/* let user-space know about this change */
+		kobject_uevent(&disk_to_dev(bdev->bd_disk)->kobj, KOBJ_CHANGE);
+	}
+	mapping_set_gfp_mask(filp->f_mapping, gfp);
+	/* This is safe: open() is still holding a reference. */
+	module_put(THIS_MODULE);
+	blk_mq_unfreeze_queue(lo->lo_queue);
+
+	partscan = lo->lo_flags & LO_FLAGS_PARTSCAN && bdev;
+	lo_number = lo->lo_number;
+	loop_unprepare_queue(lo);
+out_unlock:
+	mutex_unlock(&loop_ctl_mutex);
+	if (partscan) {
+		/*
+		 * bd_mutex has been held already in release path, so don't
+		 * acquire it if this function is called in such case.
+		 *
+		 * If the reread partition isn't from release path, lo_refcnt
+		 * must be at least one and it can only become zero when the
+		 * current holder is released.
+		 */
+		if (release)
+			err = __blkdev_reread_part(bdev);
+		else
+			err = blkdev_reread_part(bdev);
+		if (err)
+			pr_warn("%s: partition scan of loop%d failed (rc=%d)\n",
+				__func__, lo_number, err);
+		/* Device is gone, no point in returning error */
+		err = 0;
+	}
+
+	/*
+	 * lo->lo_state is set to Lo_unbound here after above partscan has
+	 * finished.
+	 *
+	 * There cannot be anybody else entering __loop_clr_fd() as
+	 * lo->lo_backing_file is already cleared and Lo_rundown state
+	 * protects us from all the other places trying to change the 'lo'
+	 * device.
+	 */
+	mutex_lock(&loop_ctl_mutex);
+	lo->lo_flags = 0;
+	if (!part_shift)
+		lo->lo_disk->flags |= GENHD_FL_NO_PART_SCAN;
+	lo->lo_state = Lo_unbound;
+	mutex_unlock(&loop_ctl_mutex);
+
+	/*
+	 * Need not hold loop_ctl_mutex to fput backing file.
+	 * Calling fput holding loop_ctl_mutex triggers a circular
+	 * lock dependency possibility warning as fput can take
+	 * bd_mutex which is usually taken before loop_ctl_mutex.
+	 */
+	if (filp)
+		fput(filp);
+	return err;
+}
+
+static int loop_clr_fd(struct loop_device *lo)
+{
+	int err;
+
+	err = mutex_lock_killable(&loop_ctl_mutex);
+	if (err)
+		return err;
+	if (lo->lo_state != Lo_bound) {
+		mutex_unlock(&loop_ctl_mutex);
+		return -ENXIO;
+	}
+	/*
+	 * If we've explicitly asked to tear down the loop device,
+	 * and it has an elevated reference count, set it for auto-teardown when
+	 * the last reference goes away. This stops $!~#$@ udev from
+	 * preventing teardown because it decided that it needs to run blkid on
+	 * the loopback device whenever they appear. xfstests is notorious for
+	 * failing tests because blkid via udev races with a losetup
+	 * <dev>/do something like mkfs/losetup -d <dev> causing the losetup -d
+	 * command to fail with EBUSY.
+	 */
+	if (atomic_read(&lo->lo_refcnt) > 1) {
+		lo->lo_flags |= LO_FLAGS_AUTOCLEAR;
+		mutex_unlock(&loop_ctl_mutex);
+		return 0;
+	}
+	lo->lo_state = Lo_rundown;
+	mutex_unlock(&loop_ctl_mutex);
+
+	return __loop_clr_fd(lo, false);
+}
+
+static int
+loop_set_status(struct loop_device *lo, const struct loop_info64 *info)
+{
+	int err;
+	struct loop_func_table *xfer;
+	kuid_t uid = current_uid();
+	struct block_device *bdev;
+	bool partscan = false;
+
+	err = mutex_lock_killable(&loop_ctl_mutex);
+	if (err)
+		return err;
+	if (lo->lo_encrypt_key_size &&
+	    !uid_eq(lo->lo_key_owner, uid) &&
+	    !capable(CAP_SYS_ADMIN)) {
+		err = -EPERM;
+		goto out_unlock;
+	}
+	if (lo->lo_state != Lo_bound) {
+		err = -ENXIO;
+		goto out_unlock;
+	}
+	if ((unsigned int) info->lo_encrypt_key_size > LO_KEY_SIZE) {
+		err = -EINVAL;
+		goto out_unlock;
+	}
+
+	if (lo->lo_offset != info->lo_offset ||
+	    lo->lo_sizelimit != info->lo_sizelimit) {
+		sync_blockdev(lo->lo_device);
+		kill_bdev(lo->lo_device);
+	}
+
+	/* I/O need to be drained during transfer transition */
+	blk_mq_freeze_queue(lo->lo_queue);
+
+	err = loop_release_xfer(lo);
+	if (err)
+		goto out_unfreeze;
+
+	if (info->lo_encrypt_type) {
+		unsigned int type = info->lo_encrypt_type;
+
+		if (type >= MAX_LO_CRYPT) {
+			err = -EINVAL;
+			goto out_unfreeze;
+		}
+		xfer = xfer_funcs[type];
+		if (xfer == NULL) {
+			err = -EINVAL;
+			goto out_unfreeze;
+		}
+	} else
+		xfer = NULL;
+
+	err = loop_init_xfer(lo, xfer, info);
+	if (err)
+		goto out_unfreeze;
+
+	if (lo->lo_offset != info->lo_offset ||
+	    lo->lo_sizelimit != info->lo_sizelimit) {
+		/* kill_bdev should have truncated all the pages */
+		if (lo->lo_device->bd_inode->i_mapping->nrpages) {
+			err = -EAGAIN;
+			pr_warn("%s: loop%d (%s) has still dirty pages (nrpages=%lu)\n",
+				__func__, lo->lo_number, lo->lo_file_name,
+				lo->lo_device->bd_inode->i_mapping->nrpages);
+			goto out_unfreeze;
+		}
+		if (figure_loop_size(lo, info->lo_offset, info->lo_sizelimit)) {
+			err = -EFBIG;
+			goto out_unfreeze;
+		}
+	}
+
+	if (lo->lo_fmt->file_fmt_type != info->lo_file_fmt_type) {
+		err = loop_file_fmt_change(lo->lo_fmt, info->lo_file_fmt_type);
+		if (err)
+			goto out_unfreeze;
+
+		/* After change of the file format, recalculate the capacity of
+		 * the loop device. figure_loop_size() automatically calls the
+		 * sector_size function of the corresponding loop file format
+		 * driver to determine the new capacity. */
+		if (figure_loop_size(lo, info->lo_offset, info->lo_sizelimit)) {
+			err = -EFBIG;
+			goto out_unfreeze;
+		}
+	}
+
+	loop_config_discard(lo);
+
+	memcpy(lo->lo_file_name, info->lo_file_name, LO_NAME_SIZE);
+	memcpy(lo->lo_crypt_name, info->lo_crypt_name, LO_NAME_SIZE);
+	lo->lo_file_name[LO_NAME_SIZE-1] = 0;
+	lo->lo_crypt_name[LO_NAME_SIZE-1] = 0;
+
+	if (!xfer)
+		xfer = &none_funcs;
+	lo->transfer = xfer->transfer;
+	lo->ioctl = xfer->ioctl;
+
+	if ((lo->lo_flags & LO_FLAGS_AUTOCLEAR) !=
+	     (info->lo_flags & LO_FLAGS_AUTOCLEAR))
+		lo->lo_flags ^= LO_FLAGS_AUTOCLEAR;
+
+	lo->lo_encrypt_key_size = info->lo_encrypt_key_size;
+	lo->lo_init[0] = info->lo_init[0];
+	lo->lo_init[1] = info->lo_init[1];
+	lo->lo_fmt->file_fmt_type = info->lo_file_fmt_type;
+	if (info->lo_encrypt_key_size) {
+		memcpy(lo->lo_encrypt_key, info->lo_encrypt_key,
+		       info->lo_encrypt_key_size);
+		lo->lo_key_owner = uid;
+	}
+
+	/* update dio if lo_offset or transfer is changed */
+	__loop_update_dio(lo, lo->use_dio);
+
+out_unfreeze:
+	blk_mq_unfreeze_queue(lo->lo_queue);
+
+	if (!err && (info->lo_flags & LO_FLAGS_PARTSCAN) &&
+	     !(lo->lo_flags & LO_FLAGS_PARTSCAN)) {
+		lo->lo_flags |= LO_FLAGS_PARTSCAN;
+		lo->lo_disk->flags &= ~GENHD_FL_NO_PART_SCAN;
+		bdev = lo->lo_device;
+		partscan = true;
+	}
+out_unlock:
+	mutex_unlock(&loop_ctl_mutex);
+	if (partscan)
+		loop_reread_partitions(lo, bdev);
+
+	return err;
+}
+
+static int
+loop_get_status(struct loop_device *lo, struct loop_info64 *info)
+{
+	struct path path;
+	struct kstat stat;
+	int ret;
+
+	ret = mutex_lock_killable(&loop_ctl_mutex);
+	if (ret)
+		return ret;
+	if (lo->lo_state != Lo_bound) {
+		mutex_unlock(&loop_ctl_mutex);
+		return -ENXIO;
+	}
+
+	memset(info, 0, sizeof(*info));
+	info->lo_number = lo->lo_number;
+	info->lo_offset = lo->lo_offset;
+	info->lo_sizelimit = lo->lo_sizelimit;
+	info->lo_flags = lo->lo_flags;
+	memcpy(info->lo_file_name, lo->lo_file_name, LO_NAME_SIZE);
+	memcpy(info->lo_crypt_name, lo->lo_crypt_name, LO_NAME_SIZE);
+	info->lo_encrypt_type =
+		lo->lo_encryption ? lo->lo_encryption->number : 0;
+	if (lo->lo_encrypt_key_size && capable(CAP_SYS_ADMIN)) {
+		info->lo_encrypt_key_size = lo->lo_encrypt_key_size;
+		memcpy(info->lo_encrypt_key, lo->lo_encrypt_key,
+		       lo->lo_encrypt_key_size);
+	}
+	info->lo_file_fmt_type = lo->lo_fmt->file_fmt_type;
+
+	/* Drop loop_ctl_mutex while we call into the filesystem. */
+	path = lo->lo_backing_file->f_path;
+	path_get(&path);
+	mutex_unlock(&loop_ctl_mutex);
+	ret = vfs_getattr(&path, &stat, STATX_INO, AT_STATX_SYNC_AS_STAT);
+	if (!ret) {
+		info->lo_device = huge_encode_dev(stat.dev);
+		info->lo_inode = stat.ino;
+		info->lo_rdevice = huge_encode_dev(stat.rdev);
+	}
+	path_put(&path);
+	return ret;
+}
+
+static void
+loop_info64_from_old(const struct loop_info *info, struct loop_info64 *info64)
+{
+	memset(info64, 0, sizeof(*info64));
+	info64->lo_number = info->lo_number;
+	info64->lo_device = info->lo_device;
+	info64->lo_inode = info->lo_inode;
+	info64->lo_rdevice = info->lo_rdevice;
+	info64->lo_offset = info->lo_offset;
+	info64->lo_sizelimit = 0;
+	info64->lo_encrypt_type = info->lo_encrypt_type;
+	info64->lo_encrypt_key_size = info->lo_encrypt_key_size;
+	info64->lo_flags = info->lo_flags;
+	info64->lo_init[0] = info->lo_init[0];
+	info64->lo_init[1] = info->lo_init[1];
+	info64->lo_file_fmt_type = info->lo_file_fmt_type;
+	if (info->lo_encrypt_type == LO_CRYPT_CRYPTOAPI)
+		memcpy(info64->lo_crypt_name, info->lo_name, LO_NAME_SIZE);
+	else
+		memcpy(info64->lo_file_name, info->lo_name, LO_NAME_SIZE);
+	memcpy(info64->lo_encrypt_key, info->lo_encrypt_key, LO_KEY_SIZE);
+}
+
+static int
+loop_info64_to_old(const struct loop_info64 *info64, struct loop_info *info)
+{
+	memset(info, 0, sizeof(*info));
+	info->lo_number = info64->lo_number;
+	info->lo_device = info64->lo_device;
+	info->lo_inode = info64->lo_inode;
+	info->lo_rdevice = info64->lo_rdevice;
+	info->lo_offset = info64->lo_offset;
+	info->lo_encrypt_type = info64->lo_encrypt_type;
+	info->lo_encrypt_key_size = info64->lo_encrypt_key_size;
+	info->lo_flags = info64->lo_flags;
+	info->lo_init[0] = info64->lo_init[0];
+	info->lo_init[1] = info64->lo_init[1];
+	info->lo_file_fmt_type = info64->lo_file_fmt_type;
+	if (info->lo_encrypt_type == LO_CRYPT_CRYPTOAPI)
+		memcpy(info->lo_name, info64->lo_crypt_name, LO_NAME_SIZE);
+	else
+		memcpy(info->lo_name, info64->lo_file_name, LO_NAME_SIZE);
+	memcpy(info->lo_encrypt_key, info64->lo_encrypt_key, LO_KEY_SIZE);
+
+	/* error in case values were truncated */
+	if (info->lo_device != info64->lo_device ||
+	    info->lo_rdevice != info64->lo_rdevice ||
+	    info->lo_inode != info64->lo_inode ||
+	    info->lo_offset != info64->lo_offset)
+		return -EOVERFLOW;
+
+	return 0;
+}
+
+static int
+loop_set_status_old(struct loop_device *lo, const struct loop_info __user *arg)
+{
+	struct loop_info info;
+	struct loop_info64 info64;
+	int err;
+
+	/* backward compatibility: copy everything except the file format type
+	 * field */
+	err = copy_from_user(&info, arg,
+		sizeof(info) - sizeof(info.lo_file_fmt_type));
+	if (err)
+		return -EFAULT;
+
+	if (info.lo_flags & LO_FLAGS_FILE_FMT) {
+		/* copy everything from the user space */
+		err = copy_from_user(&info, arg, sizeof(info));
+		if (err)
+			return -EFAULT;
+	} else {
+		info64.lo_file_fmt_type = LO_FILE_FMT_RAW;
+	}
+
+	loop_info64_from_old(&info, &info64);
+	return loop_set_status(lo, &info64);
+}
+
+static int
+loop_set_status64(struct loop_device *lo, const struct loop_info64 __user *arg)
+{
+	struct loop_info64 info64;
+	int err;
+
+	/* backward compatibility: copy everything except the file format type
+	 * field */
+	err = copy_from_user(&info64, arg,
+		sizeof(info64) - sizeof(info64.lo_file_fmt_type));
+	if (err)
+		return -EFAULT;
+
+	if (info64.lo_flags & LO_FLAGS_FILE_FMT) {
+		/* copy everything from the user space */
+		err = copy_from_user(&info64, arg, sizeof(info64));
+		if (err)
+			return -EFAULT;
+	} else {
+		info64.lo_file_fmt_type = LO_FILE_FMT_RAW;
+	}
+
+	return loop_set_status(lo, &info64);
+}
+
+static int
+loop_get_status_old(struct loop_device *lo, struct loop_info __user *arg) {
+	struct loop_info info;
+	struct loop_info64 info64;
+	int lo_flags;
+	int err;
+
+	if (!arg)
+		return -EINVAL;
+
+	/* backward compatibility: copy everything except the file format type
+	 * field */
+	err = copy_from_user(&info, arg,
+		sizeof(info) - sizeof(info.lo_file_fmt_type));
+	if (err)
+		return -EFAULT;
+
+	lo_flags = info.lo_flags;
+
+	err = loop_get_status(lo, &info64);
+	if (!err)
+		err = loop_info64_to_old(&info64, &info);
+
+	if (lo_flags & LO_FLAGS_FILE_FMT) {
+		/* copy entire structure to user space because file format
+		 * support is available */
+		err = copy_to_user(arg, &info, sizeof(info));
+	} else {
+		/* copy normal structure to user space */
+		err = copy_to_user(arg, &info,
+			sizeof(info) - sizeof(info.lo_file_fmt_type));
+	}
+
+	if (err)
+		return -EFAULT;
+
+	return err;
+}
+
+static int
+loop_get_status64(struct loop_device *lo, struct loop_info64 __user *arg) {
+	struct loop_info64 info64;
+	u32 lo_flags;
+	int err;
+
+	if (!arg)
+		return -EINVAL;
+
+	/* backward compatibility: copy everything except the file format type
+	 * field */
+	err = copy_from_user(&info64, arg,
+		sizeof(info64) - sizeof(info64.lo_file_fmt_type));
+	if (err)
+		return -EFAULT;
+
+	lo_flags = info64.lo_flags;
+
+	err = loop_get_status(lo, &info64);
+	if (err)
+		return -EFAULT;
+
+	if (lo_flags & LO_FLAGS_FILE_FMT) {
+		/* copy entire structure to user space because file format
+		 * support is available */
+		err = copy_to_user(arg, &info64, sizeof(info64));
+	} else {
+		/* copy normal structure to user space */
+		err = copy_to_user(arg, &info64,
+			sizeof(info64) - sizeof(info64.lo_file_fmt_type));
+	}
+
+	if (err)
+		return -EFAULT;
+
+	return err;
+}
+
+static int loop_set_capacity(struct loop_device *lo)
+{
+	if (unlikely(lo->lo_state != Lo_bound))
+		return -ENXIO;
+
+	return figure_loop_size(lo, lo->lo_offset, lo->lo_sizelimit);
+}
+
+static int loop_set_dio(struct loop_device *lo, unsigned long arg)
+{
+	int error = -ENXIO;
+	if (lo->lo_state != Lo_bound)
+		goto out;
+
+	__loop_update_dio(lo, !!arg);
+	if (lo->use_dio == !!arg)
+		return 0;
+	error = -EINVAL;
+ out:
+	return error;
+}
+
+static int loop_set_block_size(struct loop_device *lo, unsigned long arg)
+{
+	int err = 0;
+
+	if (lo->lo_state != Lo_bound)
+		return -ENXIO;
+
+	if (arg < 512 || arg > PAGE_SIZE || !is_power_of_2(arg))
+		return -EINVAL;
+
+	if (lo->lo_queue->limits.logical_block_size != arg) {
+		sync_blockdev(lo->lo_device);
+		kill_bdev(lo->lo_device);
+	}
+
+	blk_mq_freeze_queue(lo->lo_queue);
+
+	/* kill_bdev should have truncated all the pages */
+	if (lo->lo_queue->limits.logical_block_size != arg &&
+			lo->lo_device->bd_inode->i_mapping->nrpages) {
+		err = -EAGAIN;
+		pr_warn("%s: loop%d (%s) has still dirty pages (nrpages=%lu)\n",
+			__func__, lo->lo_number, lo->lo_file_name,
+			lo->lo_device->bd_inode->i_mapping->nrpages);
+		goto out_unfreeze;
+	}
+
+	blk_queue_logical_block_size(lo->lo_queue, arg);
+	blk_queue_physical_block_size(lo->lo_queue, arg);
+	blk_queue_io_min(lo->lo_queue, arg);
+	loop_update_dio(lo);
+out_unfreeze:
+	blk_mq_unfreeze_queue(lo->lo_queue);
+
+	return err;
+}
+
+static int lo_simple_ioctl(struct loop_device *lo, unsigned int cmd,
+			   unsigned long arg)
+{
+	int err;
+
+	err = mutex_lock_killable(&loop_ctl_mutex);
+	if (err)
+		return err;
+	switch (cmd) {
+	case LOOP_SET_CAPACITY:
+		err = loop_set_capacity(lo);
+		break;
+	case LOOP_SET_DIRECT_IO:
+		err = loop_set_dio(lo, arg);
+		break;
+	case LOOP_SET_BLOCK_SIZE:
+		err = loop_set_block_size(lo, arg);
+		break;
+	default:
+		err = lo->ioctl ? lo->ioctl(lo, cmd, arg) : -EINVAL;
+	}
+	mutex_unlock(&loop_ctl_mutex);
+	return err;
+}
+
+static int lo_ioctl(struct block_device *bdev, fmode_t mode,
+	unsigned int cmd, unsigned long arg)
+{
+	struct loop_device *lo = bdev->bd_disk->private_data;
+	int err;
+
+	switch (cmd) {
+	case LOOP_SET_FD:
+		return loop_set_fd(lo, mode, bdev, arg);
+	case LOOP_CHANGE_FD:
+		return loop_change_fd(lo, bdev, arg);
+	case LOOP_CLR_FD:
+		return loop_clr_fd(lo);
+	case LOOP_SET_STATUS:
+		err = -EPERM;
+		if ((mode & FMODE_WRITE) || capable(CAP_SYS_ADMIN)) {
+			err = loop_set_status_old(lo,
+					(struct loop_info __user *)arg);
+		}
+		break;
+	case LOOP_GET_STATUS:
+		return loop_get_status_old(lo, (struct loop_info __user *) arg);
+	case LOOP_SET_STATUS64:
+		err = -EPERM;
+		if ((mode & FMODE_WRITE) || capable(CAP_SYS_ADMIN)) {
+			err = loop_set_status64(lo,
+					(struct loop_info64 __user *) arg);
+		}
+		break;
+	case LOOP_GET_STATUS64:
+		return loop_get_status64(lo, (struct loop_info64 __user *) arg);
+	case LOOP_SET_CAPACITY:
+	case LOOP_SET_DIRECT_IO:
+	case LOOP_SET_BLOCK_SIZE:
+		if (!(mode & FMODE_WRITE) && !capable(CAP_SYS_ADMIN))
+			return -EPERM;
+		/* Fall through */
+	default:
+		err = lo_simple_ioctl(lo, cmd, arg);
+		break;
+	}
+
+	return err;
+}
+
+#ifdef CONFIG_COMPAT
+struct compat_loop_info {
+	compat_int_t	lo_number;      /* ioctl r/o */
+	compat_dev_t	lo_device;      /* ioctl r/o */
+	compat_ulong_t	lo_inode;       /* ioctl r/o */
+	compat_dev_t	lo_rdevice;     /* ioctl r/o */
+	compat_int_t	lo_offset;
+	compat_int_t	lo_encrypt_type;
+	compat_int_t	lo_encrypt_key_size;    /* ioctl w/o */
+	compat_int_t	lo_flags;       /* ioctl r/o */
+	char		lo_name[LO_NAME_SIZE];
+	unsigned char	lo_encrypt_key[LO_KEY_SIZE]; /* ioctl w/o */
+	compat_ulong_t	lo_init[2];
+	char		reserved[4];
+	compat_int_t	lo_file_fmt_type;
+} __attribute__((packed));
+
+/*
+ * Transfer 32-bit compatibility structure in userspace to 64-bit loop info
+ * - noinlined to reduce stack space usage in main part of driver
+ */
+static noinline int
+loop_info64_from_compat(const struct compat_loop_info __user *arg,
+			struct loop_info64 *info64)
+{
+	struct compat_loop_info info;
+	int err;
+
+	/* backward compatibility: copy everything except the file format type
+	 * field */
+	err = copy_from_user(&info, arg,
+		sizeof(info) - sizeof(info.lo_file_fmt_type));
+	if (err)
+		return -EFAULT;
+
+	if (info.lo_flags & LO_FLAGS_FILE_FMT) {
+		/* copy everything from the user space */
+		err = copy_from_user(&info, arg, sizeof(info));
+		if (err)
+			return -EFAULT;
+	} else {
+		info.lo_file_fmt_type = LO_FILE_FMT_RAW;
+	}
+
+	memset(info64, 0, sizeof(*info64));
+	info64->lo_number = info.lo_number;
+	info64->lo_device = info.lo_device;
+	info64->lo_inode = info.lo_inode;
+	info64->lo_rdevice = info.lo_rdevice;
+	info64->lo_offset = info.lo_offset;
+	info64->lo_sizelimit = 0;
+	info64->lo_encrypt_type = info.lo_encrypt_type;
+	info64->lo_encrypt_key_size = info.lo_encrypt_key_size;
+	info64->lo_flags = info.lo_flags;
+	info64->lo_init[0] = info.lo_init[0];
+	info64->lo_init[1] = info.lo_init[1];
+	info64->lo_file_fmt_type = info.lo_file_fmt_type;
+	if (info.lo_encrypt_type == LO_CRYPT_CRYPTOAPI)
+		memcpy(info64->lo_crypt_name, info.lo_name, LO_NAME_SIZE);
+	else
+		memcpy(info64->lo_file_name, info.lo_name, LO_NAME_SIZE);
+	memcpy(info64->lo_encrypt_key, info.lo_encrypt_key, LO_KEY_SIZE);
+	return 0;
+}
+
+/*
+ * Transfer 64-bit loop info to 32-bit compatibility structure in userspace
+ * - noinlined to reduce stack space usage in main part of driver
+ */
+static noinline int
+loop_info64_to_compat(const struct loop_info64 *info64,
+		      struct compat_loop_info __user *arg)
+{
+	struct compat_loop_info info;
+	compat_int_t lo_flags;
+	int err;
+
+	/* backward compatibility: copy everything except the file format type
+	 * field */
+	err = copy_from_user(&info, arg,
+		sizeof(info) - sizeof(info.lo_file_fmt_type));
+	if (err)
+		return -EFAULT;
+
+	lo_flags = info.lo_flags;
+
+	memset(&info, 0, sizeof(info));
+	info.lo_number = info64->lo_number;
+	info.lo_device = info64->lo_device;
+	info.lo_inode = info64->lo_inode;
+	info.lo_rdevice = info64->lo_rdevice;
+	info.lo_offset = info64->lo_offset;
+	info.lo_encrypt_type = info64->lo_encrypt_type;
+	info.lo_encrypt_key_size = info64->lo_encrypt_key_size;
+	info.lo_flags = info64->lo_flags;
+	info.lo_init[0] = info64->lo_init[0];
+	info.lo_init[1] = info64->lo_init[1];
+	info.lo_file_fmt_type = info64->lo_file_fmt_type;
+	if (info.lo_encrypt_type == LO_CRYPT_CRYPTOAPI)
+		memcpy(info.lo_name, info64->lo_crypt_name, LO_NAME_SIZE);
+	else
+		memcpy(info.lo_name, info64->lo_file_name, LO_NAME_SIZE);
+	memcpy(info.lo_encrypt_key, info64->lo_encrypt_key, LO_KEY_SIZE);
+
+	/* error in case values were truncated */
+	if (info.lo_device != info64->lo_device ||
+	    info.lo_rdevice != info64->lo_rdevice ||
+	    info.lo_inode != info64->lo_inode ||
+	    info.lo_offset != info64->lo_offset ||
+	    info.lo_init[0] != info64->lo_init[0] ||
+	    info.lo_init[1] != info64->lo_init[1] ||
+	    info.lo_file_fmt_type != info64->lo_file_fmt_type)
+		return -EOVERFLOW;
+
+	if (lo_flags & LO_FLAGS_FILE_FMT) {
+		/* copy entire structure to user space because file format
+		 * support is available */
+		err = copy_to_user(arg, &info, sizeof(info));
+	} else {
+		/* copy normal structure to user space */
+		err = copy_to_user(arg, &info,
+			sizeof(info) - sizeof(info.lo_file_fmt_type));
+	}
+
+	if (err)
+		return -EFAULT;
+
+	return 0;
+}
+
+static int
+loop_set_status_compat(struct loop_device *lo,
+		       const struct compat_loop_info __user *arg)
+{
+	struct loop_info64 info64;
+	int ret;
+
+	ret = loop_info64_from_compat(arg, &info64);
+	if (ret < 0)
+		return ret;
+	return loop_set_status(lo, &info64);
+}
+
+static int
+loop_get_status_compat(struct loop_device *lo,
+		       struct compat_loop_info __user *arg)
+{
+	struct loop_info64 info64;
+	int err;
+
+	if (!arg)
+		return -EINVAL;
+	err = loop_get_status(lo, &info64);
+	if (!err)
+		err = loop_info64_to_compat(&info64, arg);
+	return err;
+}
+
+static int lo_compat_ioctl(struct block_device *bdev, fmode_t mode,
+			   unsigned int cmd, unsigned long arg)
+{
+	struct loop_device *lo = bdev->bd_disk->private_data;
+	int err;
+
+	switch(cmd) {
+	case LOOP_SET_STATUS:
+		err = loop_set_status_compat(lo,
+			     (const struct compat_loop_info __user *)arg);
+		break;
+	case LOOP_GET_STATUS:
+		err = loop_get_status_compat(lo,
+				     (struct compat_loop_info __user *)arg);
+		break;
+	case LOOP_SET_CAPACITY:
+	case LOOP_CLR_FD:
+	case LOOP_GET_STATUS64:
+	case LOOP_SET_STATUS64:
+		arg = (unsigned long) compat_ptr(arg);
+		/* fall through */
+	case LOOP_SET_FD:
+	case LOOP_CHANGE_FD:
+	case LOOP_SET_BLOCK_SIZE:
+		err = lo_ioctl(bdev, mode, cmd, arg);
+		break;
+	default:
+		err = -ENOIOCTLCMD;
+		break;
+	}
+	return err;
+}
+#endif
+
+static int lo_open(struct block_device *bdev, fmode_t mode)
+{
+	struct loop_device *lo;
+	int err;
+
+	err = mutex_lock_killable(&loop_ctl_mutex);
+	if (err)
+		return err;
+	lo = bdev->bd_disk->private_data;
+	if (!lo) {
+		err = -ENXIO;
+		goto out;
+	}
+
+	atomic_inc(&lo->lo_refcnt);
+out:
+	mutex_unlock(&loop_ctl_mutex);
+	return err;
+}
+
+static void lo_release(struct gendisk *disk, fmode_t mode)
+{
+	struct loop_device *lo;
+
+	mutex_lock(&loop_ctl_mutex);
+	lo = disk->private_data;
+	if (atomic_dec_return(&lo->lo_refcnt))
+		goto out_unlock;
+
+	if (lo->lo_flags & LO_FLAGS_AUTOCLEAR) {
+		if (lo->lo_state != Lo_bound)
+			goto out_unlock;
+		lo->lo_state = Lo_rundown;
+		mutex_unlock(&loop_ctl_mutex);
+		/*
+		 * In autoclear mode, stop the loop thread
+		 * and remove configuration after last close.
+		 */
+		__loop_clr_fd(lo, true);
+		return;
+	} else if (lo->lo_state == Lo_bound) {
+		/*
+		 * Otherwise keep thread (if running) and config,
+		 * but flush possible ongoing bios in thread.
+		 */
+		blk_mq_freeze_queue(lo->lo_queue);
+		blk_mq_unfreeze_queue(lo->lo_queue);
+	}
+
+out_unlock:
+	mutex_unlock(&loop_ctl_mutex);
+}
+
+static const struct block_device_operations lo_fops = {
+	.owner =	THIS_MODULE,
+	.open =		lo_open,
+	.release =	lo_release,
+	.ioctl =	lo_ioctl,
+#ifdef CONFIG_COMPAT
+	.compat_ioctl =	lo_compat_ioctl,
+#endif
+};
+
+/*
+ * And now the modules code and kernel interface.
+ */
+static int max_loop;
+module_param(max_loop, int, 0444);
+MODULE_PARM_DESC(max_loop, "Maximum number of loop devices");
+module_param(max_part, int, 0444);
+MODULE_PARM_DESC(max_part, "Maximum number of partitions per loop device");
+MODULE_LICENSE("GPL");
+MODULE_ALIAS_BLOCKDEV_MAJOR(LOOP_MAJOR);
+
+int loop_register_transfer(struct loop_func_table *funcs)
+{
+	unsigned int n = funcs->number;
+
+	if (n >= MAX_LO_CRYPT || xfer_funcs[n])
+		return -EINVAL;
+	xfer_funcs[n] = funcs;
+	return 0;
+}
+
+static int unregister_transfer_cb(int id, void *ptr, void *data)
+{
+	struct loop_device *lo = ptr;
+	struct loop_func_table *xfer = data;
+
+	mutex_lock(&loop_ctl_mutex);
+	if (lo->lo_encryption == xfer)
+		loop_release_xfer(lo);
+	mutex_unlock(&loop_ctl_mutex);
+	return 0;
+}
+
+int loop_unregister_transfer(int number)
+{
+	unsigned int n = number;
+	struct loop_func_table *xfer;
+
+	if (n == 0 || n >= MAX_LO_CRYPT || (xfer = xfer_funcs[n]) == NULL)
+		return -EINVAL;
+
+	xfer_funcs[n] = NULL;
+	idr_for_each(&loop_index_idr, &unregister_transfer_cb, xfer);
+	return 0;
+}
+
+EXPORT_SYMBOL(loop_register_transfer);
+EXPORT_SYMBOL(loop_unregister_transfer);
+
+static blk_status_t loop_queue_rq(struct blk_mq_hw_ctx *hctx,
+		const struct blk_mq_queue_data *bd)
+{
+	struct request *rq = bd->rq;
+	struct loop_cmd *cmd = blk_mq_rq_to_pdu(rq);
+	struct loop_device *lo = rq->q->queuedata;
+
+	blk_mq_start_request(rq);
+
+	if (lo->lo_state != Lo_bound)
+		return BLK_STS_IOERR;
+
+	switch (req_op(rq)) {
+	case REQ_OP_FLUSH:
+	case REQ_OP_DISCARD:
+	case REQ_OP_WRITE_ZEROES:
+		cmd->use_aio = false;
+		break;
+	default:
+		cmd->use_aio = lo->use_dio;
+		break;
+	}
+
+	/* always use the first bio's css */
+#ifdef CONFIG_BLK_CGROUP
+	if (cmd->use_aio && rq->bio && rq->bio->bi_css) {
+		cmd->css = rq->bio->bi_css;
+		css_get(cmd->css);
+	} else
+#endif
+		cmd->css = NULL;
+	kthread_queue_work(&lo->worker, &cmd->work);
+
+	return BLK_STS_OK;
+}
+
+static void loop_handle_cmd(struct loop_cmd *cmd)
+{
+	struct request *rq = blk_mq_rq_from_pdu(cmd);
+	const bool write = op_is_write(req_op(rq));
+	struct loop_device *lo = rq->q->queuedata;
+	int ret = 0;
+
+	if (write && (lo->lo_flags & LO_FLAGS_READ_ONLY)) {
+		ret = -EIO;
+		goto failed;
+	}
+
+	ret = do_req_filebacked(lo, rq);
+ failed:
+	/* complete non-aio request */
+	if (!cmd->use_aio || ret) {
+		cmd->ret = ret ? -EIO : 0;
+		blk_mq_complete_request(rq);
+	}
+}
+
+static void loop_queue_work(struct kthread_work *work)
+{
+	struct loop_cmd *cmd =
+		container_of(work, struct loop_cmd, work);
+
+	loop_handle_cmd(cmd);
+}
+
+static int loop_init_request(struct blk_mq_tag_set *set, struct request *rq,
+		unsigned int hctx_idx, unsigned int numa_node)
+{
+	struct loop_cmd *cmd = blk_mq_rq_to_pdu(rq);
+
+	kthread_init_work(&cmd->work, loop_queue_work);
+	return 0;
+}
+
+static const struct blk_mq_ops loop_mq_ops = {
+	.queue_rq       = loop_queue_rq,
+	.init_request	= loop_init_request,
+	.complete	= lo_complete_rq,
+};
+
+static struct dentry *loop_dbgfs_dir;
+
+static int loop_add(struct loop_device **l, int i)
+{
+	struct loop_device *lo;
+	struct gendisk *disk;
+	int err;
+
+	err = -ENOMEM;
+	lo = kzalloc(sizeof(*lo), GFP_KERNEL);
+	if (!lo)
+		goto out;
+
+	lo->lo_state = Lo_unbound;
+
+	/* allocate id, if @id >= 0, we're requesting that specific id */
+	if (i >= 0) {
+		err = idr_alloc(&loop_index_idr, lo, i, i + 1, GFP_KERNEL);
+		if (err == -ENOSPC)
+			err = -EEXIST;
+	} else {
+		err = idr_alloc(&loop_index_idr, lo, 0, 0, GFP_KERNEL);
+	}
+	if (err < 0)
+		goto out_free_dev;
+	i = err;
+
+	err = -ENOMEM;
+	lo->tag_set.ops = &loop_mq_ops;
+	lo->tag_set.nr_hw_queues = 1;
+	lo->tag_set.queue_depth = 128;
+	lo->tag_set.numa_node = NUMA_NO_NODE;
+	lo->tag_set.cmd_size = sizeof(struct loop_cmd);
+	lo->tag_set.flags = BLK_MQ_F_SHOULD_MERGE | BLK_MQ_F_SG_MERGE;
+	lo->tag_set.driver_data = lo;
+
+	err = blk_mq_alloc_tag_set(&lo->tag_set);
+	if (err)
+		goto out_free_idr;
+
+	lo->lo_queue = blk_mq_init_queue(&lo->tag_set);
+	if (IS_ERR_OR_NULL(lo->lo_queue)) {
+		err = PTR_ERR(lo->lo_queue);
+		goto out_cleanup_tags;
+	}
+	lo->lo_queue->queuedata = lo;
+
+	blk_queue_max_hw_sectors(lo->lo_queue, BLK_DEF_MAX_SECTORS);
+
+	/*
+	 * By default, we do buffer IO, so it doesn't make sense to enable
+	 * merge because the I/O submitted to backing file is handled page by
+	 * page. For directio mode, merge does help to dispatch bigger request
+	 * to underlayer disk. We will enable merge once directio is enabled.
+	 */
+	blk_queue_flag_set(QUEUE_FLAG_NOMERGES, lo->lo_queue);
+
+	err = -ENOMEM;
+	lo->lo_fmt = loop_file_fmt_alloc();
+	if (!lo->lo_fmt)
+		goto out_free_queue;
+
+	loop_file_fmt_set_lo(lo->lo_fmt, lo);
+
+	err = -ENOMEM;
+	disk = lo->lo_disk = alloc_disk(1 << part_shift);
+	if (!disk)
+		goto out_free_file_fmt;
+
+	/*
+	 * Disable partition scanning by default. The in-kernel partition
+	 * scanning can be requested individually per-device during its
+	 * setup. Userspace can always add and remove partitions from all
+	 * devices. The needed partition minors are allocated from the
+	 * extended minor space, the main loop device numbers will continue
+	 * to match the loop minors, regardless of the number of partitions
+	 * used.
+	 *
+	 * If max_part is given, partition scanning is globally enabled for
+	 * all loop devices. The minors for the main loop devices will be
+	 * multiples of max_part.
+	 *
+	 * Note: Global-for-all-devices, set-only-at-init, read-only module
+	 * parameteters like 'max_loop' and 'max_part' make things needlessly
+	 * complicated, are too static, inflexible and may surprise
+	 * userspace tools. Parameters like this in general should be avoided.
+	 */
+	if (!part_shift)
+		disk->flags |= GENHD_FL_NO_PART_SCAN;
+	disk->flags |= GENHD_FL_EXT_DEVT;
+	atomic_set(&lo->lo_refcnt, 0);
+	lo->lo_number		= i;
+	spin_lock_init(&lo->lo_lock);
+	disk->major		= LOOP_MAJOR;
+	disk->first_minor	= i << part_shift;
+	disk->fops		= &lo_fops;
+	disk->private_data	= lo;
+	disk->queue		= lo->lo_queue;
+	sprintf(disk->disk_name, "loop%d", i);
+	add_disk(disk);
+	*l = lo;
+
+	/* initialize debugfs entries */
+	/* create for each loop device a debugfs directory under 'loop' if
+	 * the 'block' directory exists, otherwise create the loop directory in
+	 * the root directory */
+#ifdef CONFIG_DEBUG_FS
+	lo->lo_dbgfs_dir = debugfs_create_dir(disk->disk_name, loop_dbgfs_dir);
+
+	if (IS_ERR_OR_NULL(lo->lo_dbgfs_dir)) {
+		err = -ENODEV;
+		lo->lo_dbgfs_dir = NULL;
+		goto out_free_file_fmt;
+	}
+#endif
+
+	return lo->lo_number;
+
+out_free_file_fmt:
+	loop_file_fmt_free(lo->lo_fmt);
+out_free_queue:
+	blk_cleanup_queue(lo->lo_queue);
+out_cleanup_tags:
+	blk_mq_free_tag_set(&lo->tag_set);
+out_free_idr:
+	idr_remove(&loop_index_idr, i);
+out_free_dev:
+	kfree(lo);
+out:
+	return err;
+}
+
+static void loop_remove(struct loop_device *lo)
+{
+	loop_file_fmt_free(lo->lo_fmt);
+	debugfs_remove(lo->lo_dbgfs_dir);
+	del_gendisk(lo->lo_disk);
+	blk_cleanup_queue(lo->lo_queue);
+	blk_mq_free_tag_set(&lo->tag_set);
+	put_disk(lo->lo_disk);
+	kfree(lo);
+}
+
+static int find_free_cb(int id, void *ptr, void *data)
+{
+	struct loop_device *lo = ptr;
+	struct loop_device **l = data;
+
+	if (lo->lo_state == Lo_unbound) {
+		*l = lo;
+		return 1;
+	}
+	return 0;
+}
+
+static int loop_lookup(struct loop_device **l, int i)
+{
+	struct loop_device *lo;
+	int ret = -ENODEV;
+
+	if (i < 0) {
+		int err;
+
+		err = idr_for_each(&loop_index_idr, &find_free_cb, &lo);
+		if (err == 1) {
+			*l = lo;
+			ret = lo->lo_number;
+		}
+		goto out;
+	}
+
+	/* lookup and return a specific i */
+	lo = idr_find(&loop_index_idr, i);
+	if (lo) {
+		*l = lo;
+		ret = lo->lo_number;
+	}
+out:
+	return ret;
+}
+
+static struct kobject *loop_probe(dev_t dev, int *part, void *data)
+{
+	struct loop_device *lo;
+	struct kobject *kobj;
+	int err;
+
+	mutex_lock(&loop_ctl_mutex);
+	err = loop_lookup(&lo, MINOR(dev) >> part_shift);
+	if (err < 0)
+		err = loop_add(&lo, MINOR(dev) >> part_shift);
+	if (err < 0)
+		kobj = NULL;
+	else
+		kobj = get_disk_and_module(lo->lo_disk);
+	mutex_unlock(&loop_ctl_mutex);
+
+	*part = 0;
+	return kobj;
+}
+
+static long loop_control_ioctl(struct file *file, unsigned int cmd,
+			       unsigned long parm)
+{
+	struct loop_device *lo;
+	int ret;
+
+	ret = mutex_lock_killable(&loop_ctl_mutex);
+	if (ret)
+		return ret;
+
+	ret = -ENOSYS;
+	switch (cmd) {
+	case LOOP_CTL_ADD:
+		ret = loop_lookup(&lo, parm);
+		if (ret >= 0) {
+			ret = -EEXIST;
+			break;
+		}
+		ret = loop_add(&lo, parm);
+		break;
+	case LOOP_CTL_REMOVE:
+		ret = loop_lookup(&lo, parm);
+		if (ret < 0)
+			break;
+		if (lo->lo_state != Lo_unbound) {
+			ret = -EBUSY;
+			break;
+		}
+		if (atomic_read(&lo->lo_refcnt) > 0) {
+			ret = -EBUSY;
+			break;
+		}
+		lo->lo_disk->private_data = NULL;
+		idr_remove(&loop_index_idr, lo->lo_number);
+		loop_remove(lo);
+		break;
+	case LOOP_CTL_GET_FREE:
+		ret = loop_lookup(&lo, -1);
+		if (ret >= 0)
+			break;
+		ret = loop_add(&lo, -1);
+	}
+	mutex_unlock(&loop_ctl_mutex);
+
+	return ret;
+}
+
+static const struct file_operations loop_ctl_fops = {
+	.open		= nonseekable_open,
+	.unlocked_ioctl	= loop_control_ioctl,
+	.compat_ioctl	= loop_control_ioctl,
+	.owner		= THIS_MODULE,
+	.llseek		= noop_llseek,
+};
+
+static struct miscdevice loop_misc = {
+	.minor		= LOOP_CTRL_MINOR,
+	.name		= "loop-control",
+	.fops		= &loop_ctl_fops,
+};
+
+MODULE_ALIAS_MISCDEV(LOOP_CTRL_MINOR);
+MODULE_ALIAS("devname:loop-control");
+
+static int __init loop_init(void)
+{
+	int i, nr;
+	unsigned long range;
+	struct loop_device *lo;
+	int err;
+
+	part_shift = 0;
+	if (max_part > 0) {
+		part_shift = fls(max_part);
+
+		/*
+		 * Adjust max_part according to part_shift as it is exported
+		 * to user space so that user can decide correct minor number
+		 * if [s]he want to create more devices.
+		 *
+		 * Note that -1 is required because partition 0 is reserved
+		 * for the whole disk.
+		 */
+		max_part = (1UL << part_shift) - 1;
+	}
+
+	if ((1UL << part_shift) > DISK_MAX_PARTS) {
+		err = -EINVAL;
+		goto err_out;
+	}
+
+	if (max_loop > 1UL << (MINORBITS - part_shift)) {
+		err = -EINVAL;
+		goto err_out;
+	}
+
+	/*
+	 * If max_loop is specified, create that many devices upfront.
+	 * This also becomes a hard limit. If max_loop is not specified,
+	 * create CONFIG_BLK_DEV_LOOP_MIN_COUNT loop devices at module
+	 * init time. Loop devices can be requested on-demand with the
+	 * /dev/loop-control interface, or be instantiated by accessing
+	 * a 'dead' device node.
+	 */
+	if (max_loop) {
+		nr = max_loop;
+		range = max_loop << part_shift;
+	} else {
+		nr = CONFIG_BLK_DEV_LOOP_MIN_COUNT;
+		range = 1UL << MINORBITS;
+	}
+
+	err = misc_register(&loop_misc);
+	if (err < 0)
+		goto err_out;
+
+
+	if (register_blkdev(LOOP_MAJOR, "loop")) {
+		err = -EIO;
+		goto misc_out;
+	}
+
+#ifdef CONFIG_DEBUG_FS
+	loop_dbgfs_dir = debugfs_create_dir("loop", NULL);
+	if (IS_ERR_OR_NULL(loop_dbgfs_dir)) {
+		err = -ENODEV;
+		goto misc_out;
+	}
+#endif
+
+	blk_register_region(MKDEV(LOOP_MAJOR, 0), range,
+				  THIS_MODULE, loop_probe, NULL, NULL);
+
+	/* pre-create number of devices given by config or max_loop */
+	mutex_lock(&loop_ctl_mutex);
+	for (i = 0; i < nr; i++)
+		loop_add(&lo, i);
+	mutex_unlock(&loop_ctl_mutex);
+
+	printk(KERN_INFO "loop: module loaded\n");
+	return 0;
+
+misc_out:
+	misc_deregister(&loop_misc);
+err_out:
+	return err;
+}
+
+static int loop_exit_cb(int id, void *ptr, void *data)
+{
+	struct loop_device *lo = ptr;
+
+	loop_remove(lo);
+	return 0;
+}
+
+static void __exit loop_exit(void)
+{
+	unsigned long range;
+
+	range = max_loop ? max_loop << part_shift : 1UL << MINORBITS;
+
+	idr_for_each(&loop_index_idr, &loop_exit_cb, NULL);
+	idr_destroy(&loop_index_idr);
+
+	blk_unregister_region(MKDEV(LOOP_MAJOR, 0), range);
+	unregister_blkdev(LOOP_MAJOR, "loop");
+
+#ifdef CONFIG_DEBUG_FS
+	debugfs_remove(loop_dbgfs_dir);
+#endif
+
+	misc_deregister(&loop_misc);
+}
+
+module_init(loop_init);
+module_exit(loop_exit);
+
+#ifndef MODULE
+static int __init max_loop_setup(char *str)
+{
+	max_loop = simple_strtol(str, NULL, 0);
+	return 1;
+}
+
+__setup("max_loop=", max_loop_setup);
+#endif
diff --git a/loop_main.h b/loop_main.h
new file mode 100644
index 0000000..33f6578
--- /dev/null
+++ b/loop_main.h
@@ -0,0 +1,106 @@
+/*
+ * loop_main.h
+ *
+ * Written by Theodore Ts'o, 3/29/93.
+ *
+ * Copyright 1993 by Theodore Ts'o.  Redistribution of this file is
+ * permitted under the GNU General Public License.
+ */
+#ifndef _LINUX_LOOP_H
+#define _LINUX_LOOP_H
+
+#include <linux/bio.h>
+#include <linux/blkdev.h>
+#include <linux/blk-mq.h>
+#include <linux/spinlock.h>
+#include <linux/mutex.h>
+#include <linux/kthread.h>
+#include <uapi/linux/loop.h>
+
+#ifdef CONFIG_DEBUG_FS
+#include <linux/debugfs.h>
+#endif
+
+#include "loop_file_fmt.h"
+
+/* Possible states of device */
+enum {
+	Lo_unbound,
+	Lo_bound,
+	Lo_rundown,
+};
+
+struct loop_func_table;
+
+struct loop_device {
+	int		lo_number;
+	atomic_t	lo_refcnt;
+	loff_t		lo_offset;
+	loff_t		lo_sizelimit;
+	int		lo_flags;
+	int		(*transfer)(struct loop_device *, int cmd,
+				    struct page *raw_page, unsigned raw_off,
+				    struct page *loop_page, unsigned loop_off,
+				    int size, sector_t real_block);
+	char		lo_file_name[LO_NAME_SIZE];
+	char		lo_crypt_name[LO_NAME_SIZE];
+	char		lo_encrypt_key[LO_KEY_SIZE];
+	int		lo_encrypt_key_size;
+	struct loop_func_table *lo_encryption;
+	__u32           lo_init[2];
+	kuid_t		lo_key_owner;	/* Who set the key */
+	int		(*ioctl)(struct loop_device *, int cmd, 
+				 unsigned long arg); 
+
+	struct loop_file_fmt *lo_fmt;
+
+	struct file *	lo_backing_file;
+	struct block_device *lo_device;
+	void		*key_data; 
+
+	gfp_t		old_gfp_mask;
+
+	spinlock_t		lo_lock;
+	int			lo_state;
+	struct kthread_worker	worker;
+	struct task_struct	*worker_task;
+	bool			use_dio;
+	bool			sysfs_inited;
+
+	struct request_queue	*lo_queue;
+	struct blk_mq_tag_set	tag_set;
+	struct gendisk		*lo_disk;
+
+#ifdef CONFIG_DEBUG_FS
+	struct dentry *lo_dbgfs_dir;
+#endif
+};
+
+struct loop_cmd {
+	struct kthread_work work;
+	bool use_aio; /* use AIO interface to handle I/O */
+	atomic_t ref; /* only for aio */
+	long ret;
+	struct kiocb iocb;
+	struct bio_vec *bvec;
+	struct cgroup_subsys_state *css;
+};
+
+/* Support for loadable transfer modules */
+struct loop_func_table {
+	int number;	/* filter type */ 
+	int (*transfer)(struct loop_device *lo, int cmd,
+			struct page *raw_page, unsigned raw_off,
+			struct page *loop_page, unsigned loop_off,
+			int size, sector_t real_block);
+	int (*init)(struct loop_device *, const struct loop_info64 *); 
+	/* release is called from loop_unregister_transfer or clr_fd */
+	int (*release)(struct loop_device *); 
+	int (*ioctl)(struct loop_device *, int cmd, unsigned long arg);
+	struct module *owner;
+}; 
+
+int loop_register_transfer(struct loop_func_table *funcs);
+int loop_unregister_transfer(int number); 
+
+#endif