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CONFIG_BLK_DEV_LOOP: Loopback device support

General informations

The Linux kernel configuration item CONFIG_BLK_DEV_LOOP has multiple definitions:

Loopback device support found in arch/ia64/Kconfig

The configuration item CONFIG_BLK_DEV_LOOP:

Help text

(none)

Loopback device support found in arch/sparc/Kconfig

The configuration item CONFIG_BLK_DEV_LOOP:

Help text

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.

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. If you want to do this, you will first have to acquire and install a kernel patch from <ftp://ftp.kerneli.org/pub/kerneli/>, and then you need to say Y to this option.

Note that alternative ways to use encrypted file systems are provided by the cfs package, which can be gotten from <ftp://ftp.kerneli.org/pub/kerneli/net-source/>, and the newer tcfs package, available at http://tcfs.dia.unisa.it/. You do not need to say Y here if you want to use one of these. However, using cfs requires saying Y to "NFS file system support" below while using tcfs requires applying a kernel patch. An alternative steganography solution is provided by StegFS, also available from <ftp://ftp.kerneli.org/pub/kerneli/net-source/>.

To use the loop device, you need the losetup utility and a recent version of the mount program, both contained in the util-linux package. The location and current version number of util-linux is contained in the file Documentation/Changes.

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.

Loopback device support found in arch/sparc64/Kconfig

The configuration item CONFIG_BLK_DEV_LOOP:

Help text

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.

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. If you want to do this, you will first have to acquire and install a kernel patch from <ftp://ftp.kerneli.org/pub/kerneli/>, and then you need to say Y to this option.

Note that alternative ways to use encrypted file systems are provided by the cfs package, which can be gotten from <ftp://ftp.kerneli.org/pub/kerneli/net-source/>, and the newer tcfs package, available at http://tcfs.dia.unisa.it/. You do not need to say Y here if you want to use one of these. However, using cfs requires saying Y to "NFS file system support" below while using tcfs requires applying a kernel patch. An alternative steganography solution is provided by StegFS, also available from <ftp://ftp.kerneli.org/pub/kerneli/net-source/>.

To use the loop device, you need the losetup utility and a recent version of the mount program, both contained in the util-linux package. The location and current version number of util-linux is contained in the file Documentation/Changes.

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.

Loopback device support found in arch/um/Kconfig_block

The configuration item CONFIG_BLK_DEV_LOOP:

Help text

(none)

Loopback device support found in drivers/block/Kconfig

The configuration item CONFIG_BLK_DEV_LOOP:

Help text

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 <ftp://ftp.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.

Hardware

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