Re: btrfs subvolume list for not mounted filesystem?

[Andrei Borzenkov <arvidjaar@gmail.com>]

18.12.2017 19:49, Ulli Horlacher пишет:
> I want to mount an alternative subvolume of a btrfs filesystem.
> I can list the subvolumes when the filesystem is mounted, but how do I
> know them, when the filesystem is not mounted? Is there a query command?
> 
> root@xerus:~# mount | grep /test
> /dev/sdd4 on /test type btrfs (rw,relatime,space_cache,user_subvol_rm_allowed,subvolid=5,subvol=/)
> 
> root@xerus:~# btrfs subvolume list /test
> ID 258 gen 156 top level 5 path tux/zz
> ID 259 gen 156 top level 5 path tux/z1
> ID 260 gen 156 top level 5 path tmp/zz
> ID 261 gen 19 top level 260 path tmp/zz/z1
> ID 269 gen 156 top level 5 path tux/test
> ID 271 gen 129 top level 269 path tux/test/.snapshot/2017-12-02_1341.test
> 
> root@xerus:~# umount /test
> 
> root@xerus:~# btrfs subvolume list /dev/sdd4
> ERROR: not a btrfs filesystem: /dev/sdd4
> ERROR: can't access '/dev/sdd4'
> 
> 
> 

btrfs-debug-tree -r /dev/sdd4

(or in more recent btrfs-progs, "btrfs inspect-internal dump-tree") will
show subvolume IDs (as ROOT_ITEM); I'm not sure of there is simple way
to resolve subvolume path names on unmounted device.