13.07.2019 2:17, Ulli Horlacher пишет: > I need to find (all) subvolume directories. > I know, btrfs subvolumes root directories have inode #256, but a > "find / -inum 256" is horrible slow! > > Next idea: "btrfs subvolume list /" is really fast, but its output is not > always direct usable to find the subvolume directory. > > Example output on a SUSE system: > > root@trulla:~# btrfs subvolume list / > ID 257 gen 2280099 top level 5 path @ > ID 258 gen 2280769 top level 257 path @/home > ID 259 gen 2280947 top level 257 path @/opt > ID 260 gen 2280098 top level 257 path @/srv > ID 261 gen 2280954 top level 257 path @/tmp > ID 262 gen 2280187 top level 257 path @/usr/local > ID 263 gen 2280099 top level 257 path @/var/crash > ID 264 gen 2280949 top level 257 path @/var/log > ID 265 gen 2280099 top level 257 path @/var/opt > ID 266 gen 2280954 top level 257 path @/var/spool > ID 267 gen 2280947 top level 257 path @/var/tmp > ID 270 gen 2280222 top level 257 path @/.snapshots > ID 453 gen 2280954 top level 270 path @/.snapshots/128/snapshot > ID 1235 gen 2280099 top level 257 path @/var/lib/machines > ID 12392 gen 2123118 top level 270 path @/.snapshots/1065/snapshot > ID 12393 gen 2123120 top level 270 path @/.snapshots/1066/snapshot > ID 13273 gen 2176640 top level 270 path @/.snapshots/1089/snapshot > ID 13274 gen 2176651 top level 270 path @/.snapshots/1090/snapshot > ID 13553 gen 2203681 top level 270 path @/.snapshots/1103/snapshot > > There is no /@/ directory in the default filesystem because of: > > root@trulla:/# stat /@/.snapshots/128/snapshot > stat: cannot stat '/@/.snapshots/128/snapshot': No such file or directory > > root@trulla:~# btrfs subvolume get-default / > ID 453 gen 2280954 top level 270 path @/.snapshots/128/snapshot > > root@trulla:/# mount | grep " / " > /dev/sda2 on / type btrfs > (rw,relatime,space_cache,subvolid=453,subvol=/@/.snapshots/128/snapshot) > > On this particular system I could remove "@" from the subvolume path to > get the subvolume directory: >
That is just coincidence because @/.snapshot subvolume is mounted on /.snapshot. It could also be mounted under /var/lib/snapper (insert your path here). > root@trulla:/# stat /.snapshots/128/snapshot > File: '/.snapshots/128/snapshot' > Size: 198 Blocks: 0 IO Block: 4096 directory > Device: 27h/39d Inode: 256 Links: 1 > Access: (0755/drwxr-xr-x) Uid: ( 0/ root) Gid: ( 0/ root) > Access: 2019-07-13 01:03:08.543830085 +0200 > Modify: 2019-07-13 01:03:37.336445461 +0200 > Change: 2019-07-13 01:03:37.336445461 +0200 > Birth: - > > But what if a btrfs filesystem does not have a toplevel /@/ directory, but > anything else, like /this/is/my/top/directory ? > btrfs does not have "top level directory" beyond single /. It is entirely up to the user who creates it how subvolumes are named and structured. You can well have /foo, /bar, /baz mounted as /, /var and /home. > Will be the first output line of "btrfs subvolume list /" > always look like > > ID 257 gen 2280099 top level 5 path this/is/my/top/directory > > ? > If /foo and /foo/bar are subvolumes, then /foo/bar will have higher ID than /foo (because it must have been created after /foo) so /foo will be listed before /foo/bar in default sort order. Whether it will have ID 257 is entirely up to whoever created this filesytsem and its history.
