Here is structure of snapshots in openSUSE; all snapshots of root volume
are created under /.snapshots subvolume:
linux-gtrk:/host/home/src/python-btrfs/examples # sudo mount -o
ro,subvol=/ /dev/sda3 /mnt
linux-gtrk:/host/home/src/python-btrfs/examples #
./show_directory_contents.py /mnt/
directory /mnt/@ tree 257 inum 256
inode generation 6 transid 315 size 72 nbytes 0 block_group 0 mode 40755
nlink 1 uid 0 gid 0 rdev 0 flags 0x0(none)
inode ref index 0 name utf-8 ..
...
dir item list hash 1921786525 size 1
dir item location (258 ROOT_ITEM -1) type DIR name utf-8 .snapshots
...
linux-gtrk:/host/home/src/python-btrfs/examples #
./show_directory_contents.py /mnt/@/.snapshots/251/snapshot/
directory /mnt/@/.snapshots/251/snapshot/ tree 774 inum 256
inode generation 6 transid 15867 size 164 nbytes 0 block_group 0 mode
40755 nlink 1 uid 0 gid 0 rdev 0 flags 0x0(none)
inode ref index 0 name utf-8 ..
...
dir item list hash 1921786525 size 1
dir item location (258 ROOT_ITEM -1) type DIR name utf-8 .snapshots
...
linux-gtrk:/host/home/src/python-btrfs/examples #
Note that both directory items in /mnt/@ and
/mnt/@/.snapshots/251/snapshot store the same tree ID for .snapshots
item - 258. This causes grub2 btrfs driver loop - when it comes to
/mnt/@/.snapshots/251/snapshot and looks for .snapshots it jumps back to
/mnt/@/.snapshots tree.
I see that in Linux kernel somehow distinguishes between both of them; I
am not sure how it actually does it though.
What on-disk information should we check to find out "orphaned" snapshot
directory?
TIA
-andrei
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