Added file format file format subsystem for loop devices

The loop device module is extended by a file format subsystem to allow the
implementation of various disk file formats. The file format drivers are
implemented as own kernel modules and registered by the subsystem. The
subsystem takes control over the specified file format at loop creation and
calls the corresponding file format driver functions.

At the moment, the file format subsystem can handle ...

  - read
  - write
  - discard
  - flush
  - sector size

... operations of loop devices.

The file format of each loop device can be specified by the LOOP_CONFIGURE
LOOP_SET_STATUS or LOOP_SET_STATUS64 ioctl with the corresponding data
structure loop_info or respectively loop_info64.

1 files changed, 152 insertions, 129 deletions

diff --git a/loop_file_fmt.h b/loop_file_fmt.h
index 8a16c86..38d6a3b 100644
--- a/loop_file_fmt.h
+++ b/loop_file_fmt.h
@@ -2,102 +2,109 @@
 /*
  * loop_file_fmt.h
  *
- * File format subsystem for the loop device module.
+ * File format subsystem for the xloop device module.
  *
  * Copyright (C) 2019 Manuel Bentele <development@manuel-bentele.de>
  */
 
-#ifndef _LINUX_LOOP_FILE_FMT_H
-#define _LINUX_LOOP_FILE_FMT_H
+#ifndef _LINUX_XLOOP_FILE_FMT_H
+#define _LINUX_XLOOP_FILE_FMT_H
 
 #include "loop_main.h"
 
-struct loop_file_fmt;
+struct xloop_file_fmt;
 
-#define LO_FILE_FMT_RAW         0
-#define LO_FILE_FMT_QCOW        1
-#define LO_FILE_FMT_VDI         2
-#define LO_FILE_FMT_VMDK        3
-#define MAX_LO_FILE_FMT         (LO_FILE_FMT_VMDK + 1)
+#define XLO_FILE_FMT_RAW         0
+#define XLO_FILE_FMT_QCOW        1
+#define XLO_FILE_FMT_VDI         2
+#define XLO_FILE_FMT_VMDK        3
+#define MAX_XLO_FILE_FMT         (XLO_FILE_FMT_VMDK + 1)
 
 /**
- * struct loop_file_fmt_ops - File format subsystem operations
+ * struct xloop_file_fmt_ops - File format subsystem operations
  *
  * Data structure representing the file format subsystem interface.
  */
-struct loop_file_fmt_ops {
+struct xloop_file_fmt_ops {
 	/**
 	 * @init: Initialization callback function
 	 */
-	int (*init) (struct loop_file_fmt *lo_fmt);
+	int (*init) (struct xloop_file_fmt *xlo_fmt);
 
 	/**
 	 * @exit: Release callback function
 	 */
-	void (*exit) (struct loop_file_fmt *lo_fmt);
+	void (*exit) (struct xloop_file_fmt *xlo_fmt);
 
 	/**
 	 * @read: Read IO callback function
 	 */
-	int (*read) (struct loop_file_fmt *lo_fmt,
-		     struct request *rq);
+	int (*read) (struct xloop_file_fmt *xlo_fmt,
+			struct request *rq);
 
 	/**
 	 * @write: Write IO callback function
 	 */
-	int (*write) (struct loop_file_fmt *lo_fmt,
-		      struct request *rq);
+	int (*write) (struct xloop_file_fmt *xlo_fmt,
+			struct request *rq);
 
 	/**
 	 * @read_aio: Asynchronous read IO callback function
 	 */
-	int (*read_aio) (struct loop_file_fmt *lo_fmt,
-			 struct request *rq);
+	int (*read_aio) (struct xloop_file_fmt *xlo_fmt,
+			struct request *rq);
 
 	/**
 	 * @write_aio: Asynchronous write IO callback function
 	 */
-	int (*write_aio) (struct loop_file_fmt *lo_fmt,
-			  struct request *rq);
+	int (*write_aio) (struct xloop_file_fmt *xlo_fmt,
+			struct request *rq);
+
+	/**
+	 * @zero: Zero (discard) IO callback function
+	 */
+	int (*write_zeros) (struct xloop_file_fmt *xlo_fmt,
+			struct request *rq);
 
 	/**
 	 * @discard: Discard IO callback function
 	 */
-	int (*discard) (struct loop_file_fmt *lo_fmt,
+	int (*discard) (struct xloop_file_fmt *xlo_fmt,
 			struct request *rq);
 
 	/**
 	 * @flush: Flush callback function
 	 */
-	int (*flush) (struct loop_file_fmt *lo_fmt);
+	int (*flush) (struct xloop_file_fmt *xlo_fmt);
 
 	/**
 	 * @sector_size: Get sector size callback function
 	 */
-	loff_t (*sector_size) (struct loop_file_fmt *lo_fmt);
+	loff_t (*sector_size) (struct xloop_file_fmt *xlo_fmt,
+				struct file *file, loff_t offset, loff_t sizelimit);
 };
 
 /**
- * struct loop_file_fmt_driver - File format subsystem driver
+ * struct xloop_file_fmt_driver - File format subsystem driver
  *
  * Data structure to implement file format drivers for the file format
  * subsystem.
  */
-struct loop_file_fmt_driver {
+struct xloop_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
+	 * @file_fmt_type: xloop 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;
+	struct xloop_file_fmt_ops *ops;
 
 	/**
 	 * @ops: Owner of the file format driver
@@ -109,26 +116,26 @@ struct loop_file_fmt_driver {
  * states of the file format
  *
  * transitions:
- *                    loop_file_fmt_init(...)
+ *                    xloop_file_fmt_init(...)
  * ---> uninitialized ------------------------------> initialized
- *                    loop_file_fmt_exit(...)
+ *                    xloop_file_fmt_exit(...)
  *      initialized   ------------------------------> uninitialized
- *                    loop_file_fmt_read(...)
+ *                    xloop_file_fmt_read(...)
  *      initialized   ------------------------------> initialized
- *                    loop_file_fmt_read_aio(...)
+ *                    xloop_file_fmt_read_aio(...)
  *      initialized   ------------------------------> initialized
- *                    loop_file_fmt_write(...)
+ *                    xloop_file_fmt_write(...)
  *      initialized   ------------------------------> initialized
- *                    loop_file_fmt_write_aio(...)
+ *                    xloop_file_fmt_write_aio(...)
  *      initialized   ------------------------------> initialized
- *                    loop_file_fmt_discard(...)
+ *                    xloop_file_fmt_discard(...)
  *      initialized   ------------------------------> initialized
- *                    loop_file_fmt_flush(...)
+ *                    xloop_file_fmt_flush(...)
  *      initialized   ------------------------------> initialized
- *                    loop_file_fmt_sector_size(...)
+ *                    xloop_file_fmt_sector_size(...)
  *      initialized   ------------------------------> initialized
  *
- *                    loop_file_fmt_change(...)
+ *                    xloop_file_fmt_change(...)
  *    +-----------------------------------------------------------+
  *    |               exit(...)              init(...)            |
  *    | initialized   -------> uninitialized -------> initialized |
@@ -140,25 +147,25 @@ enum {
 };
 
 /**
- * struct loop_file_fmt - Loop file format
+ * struct xloop_file_fmt - xloop file format
  *
- * Data structure to use with the file format the loop file format subsystem.
+ * Data structure to use with the file format the xloop file format subsystem.
  */
-struct loop_file_fmt {
+struct xloop_file_fmt {
 	/**
-	 * @file_fmt_type: Current type of the loop file format
+	 * @file_fmt_type: Current type of the xloop file format
 	 */
 	u32 file_fmt_type;
 
 	/**
-	 * @file_fmt_state: Current state of the loop file format
+	 * @file_fmt_state: Current state of the xloop file format
 	 */
 	int file_fmt_state;
 
 	/**
-	 * @lo: Link to a file format's loop device
+	 * @xlo: Link to a file format's xloop device
 	 */
-	struct loop_device *lo;
+	struct xloop_device *xlo;
 
 	/**
 	 * @private_data: Optional link to a file format's driver specific data
@@ -170,188 +177,204 @@ struct loop_file_fmt {
 /* subsystem functions for the driver implementation */
 
 /**
- * loop_file_fmt_register_driver - Register a loop file format driver
+ * xloop_file_fmt_register_driver - Register a xloop file format driver
  * @drv: File format driver
  *
- * Registers the specified loop file format driver @drv by the loop file format
+ * Registers the specified xloop file format driver @drv by the xloop file format
  * subsystem.
  */
-extern int loop_file_fmt_register_driver(struct loop_file_fmt_driver *drv);
+extern int xloop_file_fmt_register_driver(struct xloop_file_fmt_driver *drv);
 
 /**
- * loop_file_fmt_unregister_driver - Unregister a loop file format driver
+ * xloop_file_fmt_unregister_driver - Unregister a xloop file format driver
  * @drv: File format driver
  *
- * Unregisters the specified loop file format driver @drv from the loop file
+ * Unregisters the specified xloop file format driver @drv from the xloop file
  * format subsystem.
  */
-extern void loop_file_fmt_unregister_driver(struct loop_file_fmt_driver *drv);
+extern void xloop_file_fmt_unregister_driver(struct xloop_file_fmt_driver *drv);
 
 
 /* subsystem functions for subsystem usage */
 
 /**
- * loop_file_fmt_alloc - Allocate a loop file format
+ * xloop_file_fmt_alloc - Allocate a xloop file format
  *
- * Dynamically allocates a loop file format and returns a pointer to the
- * created loop file format.
+ * Dynamically allocates a xloop file format and returns a pointer to the
+ * created xloop file format.
  */
-extern struct loop_file_fmt *loop_file_fmt_alloc(void);
+extern struct xloop_file_fmt *xloop_file_fmt_alloc(void);
 
 /**
- * loop_file_fmt_free - Free an allocated loop file format
- * @lo_fmt: Loop file format
+ * xloop_file_fmt_free - Free an allocated xloop file format
+ * @xlo_fmt: xloop file format
  *
- * Frees the already allocated loop file format @lo_fmt.
+ * Frees the already allocated xloop file format @xlo_fmt.
  */
-extern void loop_file_fmt_free(struct loop_file_fmt *lo_fmt);
+extern void xloop_file_fmt_free(struct xloop_file_fmt *xlo_fmt);
 
 /**
- * loop_file_fmt_set_lo - Set the loop file format's loop device
- * @lo_fmt: Loop file format
- * @lo: Loop device
+ * xloop_file_fmt_set_xlo - Set the xloop file format's xloop device
+ * @xlo_fmt: xloop file format
+ * @xlo: xloop device
  *
- * The link to the loop device @lo is set in the loop file format @lo_fmt.
+ * The link to the xloop device @xlo is set in the xloop file format @xlo_fmt.
  */
-extern int loop_file_fmt_set_lo(struct loop_file_fmt *lo_fmt,
-				struct loop_device *lo);
+extern int xloop_file_fmt_set_xlo(struct xloop_file_fmt *xlo_fmt,
+				struct xloop_device *xlo);
 
 /**
- * loop_file_fmt_get_lo - Get the loop file format's loop device
- * @lo_fmt: Loop file format
+ * xloop_file_fmt_get_xlo - Get the xloop file format's xloop device
+ * @xlo_fmt: xloop file format
  *
- * Returns a pointer to the loop device of the loop file format @lo_fmt.
+ * Returns a pointer to the xloop device of the xloop file format @xlo_fmt.
  */
-extern struct loop_device *loop_file_fmt_get_lo(struct loop_file_fmt *lo_fmt);
+extern struct xloop_device *xloop_file_fmt_get_xlo(struct xloop_file_fmt *xlo_fmt);
 
 /**
- * loop_file_fmt_init - Initialize a loop file format
- * @lo_fmt: Loop file format
+ * xloop_file_fmt_init - Initialize a xloop file format
+ * @xlo_fmt: xloop file format
  * @file_fmt_type: Type of the file format
  *
- * Initializes the specified loop file format @lo_fmt and sets up the correct
+ * Initializes the specified xloop file format @xlo_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
+ * xloop file format driver is loaded in the subsystems backend. If no xloop 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,
+extern int xloop_file_fmt_init(struct xloop_file_fmt *xlo_fmt,
 			      u32 file_fmt_type);
 
 /**
- * loop_file_fmt_exit - Release a loop file format
- * @lo_fmt: Loop file format
+ * xloop_file_fmt_exit - Release a xloop file format
+ * @xlo_fmt: xloop file format
  *
- * Releases the specified loop file format @lo_fmt and all its resources.
+ * Releases the specified xloop file format @xlo_fmt and all its resources.
  */
-extern void loop_file_fmt_exit(struct loop_file_fmt *lo_fmt);
+extern void xloop_file_fmt_exit(struct xloop_file_fmt *xlo_fmt);
 
 /**
- * loop_file_fmt_read - Read IO from a loop file format
- * @lo_fmt: Loop file format
+ * xloop_file_fmt_read - Read IO from a xloop file format
+ * @xlo_fmt: xloop 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.
+ * Reads IO from the file format's xloop device by sending the IO read request
+ * @rq to the xloop file format subsystem. The subsystem calls the registered
+ * callback function of the suitable xloop file format driver.
  */
-extern int loop_file_fmt_read(struct loop_file_fmt *lo_fmt,
+extern int xloop_file_fmt_read(struct xloop_file_fmt *xlo_fmt,
 			      struct request *rq);
 
 /**
- * loop_file_fmt_read_aio - Read IO from a loop file format asynchronously
- * @lo_fmt: Loop file format
+ * xloop_file_fmt_read_aio - Read IO from a xloop file format asynchronously
+ * @xlo_fmt: xloop 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
+ * Reads IO from the file format's xloop device asynchronously by sending the
+ * IO read aio request @rq to the xloop file format subsystem. The subsystem
+ * calls the registered callback function of the suitable xloop file format
  * driver.
  */
-extern int loop_file_fmt_read_aio(struct loop_file_fmt *lo_fmt,
+extern int xloop_file_fmt_read_aio(struct xloop_file_fmt *xlo_fmt,
 				  struct request *rq);
 
 /**
- * loop_file_fmt_write - Write IO to a loop file format
- * @lo_fmt: Loop file format
+ * xloop_file_fmt_write - Write IO to a xloop file format
+ * @xlo_fmt: xloop 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.
+ * Write IO to the file format's xloop device by sending the IO write request
+ * @rq to the xloop file format subsystem. The subsystem calls the registered
+ * callback function of the suitable xloop file format driver.
  */
-extern int loop_file_fmt_write(struct loop_file_fmt *lo_fmt,
+extern int xloop_file_fmt_write(struct xloop_file_fmt *xlo_fmt,
 			       struct request *rq);
 
 /**
- * loop_file_fmt_write_aio - Write IO to a loop file format asynchronously
- * @lo_fmt: Loop file format
+ * xloop_file_fmt_write_aio - Write IO to a xloop file format asynchronously
+ * @xlo_fmt: xloop 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
+ * Write IO to the file format's xloop device asynchronously by sending the
+ * IO write aio request @rq to the xloop file format subsystem. The subsystem
+ * calls the registered callback function of the suitable xloop file format
  * driver.
  */
-extern int loop_file_fmt_write_aio(struct loop_file_fmt *lo_fmt,
+extern int xloop_file_fmt_write_aio(struct xloop_file_fmt *xlo_fmt,
 				   struct request *rq);
 
 /**
- * loop_file_fmt_discard - Discard IO on a loop file format
- * @lo_fmt: Loop file format
+ * xloop_file_fmt_write_zeros - Zero (discard) IO on a xloop file format
+ * @xlo_fmt: xloop file format
+ * @rq: IO Request
+ *
+ * Zero (discard) IO on the file format's xloop device by sending the IO write
+ * zeros request @rq to the xloop file format subsystem. The subsystem calls the
+ * registered callback function of the suitable xloop file format driver.
+ */
+extern int xloop_file_fmt_write_zeros(struct xloop_file_fmt *xlo_fmt,
+				 struct request *rq);
+
+/**
+ * xloop_file_fmt_discard - Discard IO on a xloop file format
+ * @xlo_fmt: xloop 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.
+ * Discard IO on the file format's xloop device by sending the IO discard
+ * request @rq to the xloop file format subsystem. The subsystem calls the
+ * registered callback function of the suitable xloop file format driver.
  */
-extern int loop_file_fmt_discard(struct loop_file_fmt *lo_fmt,
+extern int xloop_file_fmt_discard(struct xloop_file_fmt *xlo_fmt,
 				 struct request *rq);
 
 /**
- * loop_file_fmt_flush - Flush a loop file format
- * @lo_fmt: Loop file format
+ * xloop_file_fmt_flush - Flush a xloop file format
+ * @xlo_fmt: xloop file format
  *
- * Flush the file format's loop device by calling the registered callback
- * function of the suitable loop file format driver.
+ * Flush the file format's xloop device by calling the registered callback
+ * function of the suitable xloop file format driver.
  */
-extern int loop_file_fmt_flush(struct loop_file_fmt *lo_fmt);
+extern int xloop_file_fmt_flush(struct xloop_file_fmt *xlo_fmt);
 
 /**
- * loop_file_fmt_sector_size - Get sector size of a loop file format
- * @lo_fmt: Loop file format
+ * xloop_file_fmt_sector_size - Get sector size of a xloop file format
+ * @xlo_fmt: xloop file format
+ * @file: xloop file formats file for sector size calculation
+ * @offset: Offset within the file for sector size calculation
+ * @sizelimit: Sizelimit of the file for sector size calculation
  *
- * 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
+ * Returns the physical sector size of the given xloop file format's file.
+ * If the xloop 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);
+extern loff_t xloop_file_fmt_sector_size(struct xloop_file_fmt *xlo_fmt,
+				struct file *file, loff_t offset, loff_t sizelimit);
 
 /**
- * loop_file_fmt_change - Change the loop file format's type
- * @lo_fmt: Loop file format
- * @file_fmt_type_new: Loop file format type
+ * xloop_file_fmt_change - Change the xloop file format's type
+ * @xlo_fmt: xloop file format
+ * @file_fmt_type_new: xloop 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
+ * Changes the file format type of the already initialized xloop file format
+ * @xlo_fmt. Therefore, the function releases the old file format and frees all
+ * of its resources before the xloop file format @xlo_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,
+extern int xloop_file_fmt_change(struct xloop_file_fmt *xlo_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
+ * xloop_file_fmt_print_type - Convert file format type to string
+ * @file_fmt_type: xloop file format type
+ * @file_fmt_name: xloop 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,
+extern ssize_t xloop_file_fmt_print_type(u32 file_fmt_type,
 					char *file_fmt_name);
 
 #endif