loopback设备可以使用文件作为块设备

Linux loop devices provide a way to mount ordinary files as block devices.

This capability allows you to easily access an ISO image that resides on disk,

mount and unmount encrypted devices(the dm-crypt and fuse encryption module

may be better solution for this.), or test out new file systems using plain old files.

 

Linux loop devices are managed through the losetup utility, which has options to add

list, remove and locate unused loop devices. To associate a loop device with a file, you will

first need to locate an unused loop device in /dev. This can be accomplished by running

losetup with the "-f"(find an unused loop device) option:

losetup -f

/dev/loop0

 

Once you indentity an available loop device, you can associate the loop device with a file by running

losetup with the name of the loop device, and the file to associate with the loop device:

losetup /dev/loop0 /root/foo

 

To verify the device is attached, you can run losetup with the "-a"(show all loop devices) or "-j"(show

loop devices associate with the cooresponding file)option:

losetup -a

/dev/loop0"[0801]:12779871(/root/foo)

 

To access the contents of a loop device, you can use the mount utility to mount the loop device to

a directory that resides in an existing file system:

mount /dev/loop0 /mnt

 

This of course assumes that the underlying file contains a valid label and file system(you can run

fdisk or parted to create a label, and then use your favorite mkfs variation to create a file system).

Once you finish using a loop device, you can remove it by running losetup with the "-d"(remove

loop device) option:

umount /mnt

losetup -d /dev/loop0

losetup -a

I have come to rely on loop devices for all sorts of purposes, and their simplicity makes them

so so useful!