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# 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.
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