A documentação para isso está na página man de btrfs :
It is possible to abbreviate the commands unless the commands are ambiguous. For example: it is possible to run
btrfs sub snapsinstead ofbtrfs subvolume snapshot. Butbtrfs file sis not allowed, becausefile smay be interpreted both asfilesystem showand asfilesystem sync. If a command is terminated by--help, the detailed help is showed. If the passed command matches more commands, detailed help of all the matched commands is showed. For examplebtrfs dev --helpshows the help of alldevice*commands.