losetup 用于将 Loop 设备与常规文件或块设备相关联，分离 Loop 设备并查询 Loop 设备的状态。

概要

Get info:
losetup loopdev
losetup -a
losetup -j file [-o offset]

Delete loop:
losetup -d loopdev...

Print name of first unused loop device:
losetup -f

Setup loop device:
losetup [{-e|-E} encryption] [-o offset] [--sizelimit limit][-p pfd] [-r] {-f[--show]|loopdev} file

Resize loop device:
losetup -c loopdev

参数

 -a, --all                     list all used devices
 -d, --detach <loopdev>...     detach one or more devices
 -D, --detach-all              detach all used devices
 -f, --find                    find first unused device
 -c, --set-capacity <loopdev>  resize the device
 -j, --associated <file>       list all devices associated with <file>
 -L, --nooverlap               avoid possible conflict between devices

 -o, --offset <num>            start at offset <num> into file
     --sizelimit <num>         device is limited to <num> bytes of the file
 -b, --sector-size <num>       set the logical sector size to <num>
 -P, --partscan                create a partitioned loop device
 -r, --read-only               set up a read-only loop device
     --direct-io[=<on|off>]    open backing file with O_DIRECT
     --show                    print device name after setup (with -f)
 -v, --verbose                 verbose mode

 -J, --json                    use JSON --list output format
 -l, --list                    list info about all or specified (default)
 -n, --noheadings              don't print headings for --list output
 -O, --output <cols>           specify columns to output for --list
     --output-all              output all columns
     --raw                     use raw --list output format

 -h, --help                    display this help
 -V, --version                 display version