07.07.2019 9:43, Nikolay Borisov пишет: > > > On 6.07.19 г. 23:43 ч., Ulli Horlacher wrote: >> On Sat 2019-07-06 (19:57), Nikolay Borisov wrote: >> >>>> And how can I see whether /test/tmp/xx/ss1 is a snapshot at all? >>>> Do all snapshots have a "Parent UUID" and regular subvolumes not? >>> >>> Indeed, only snapshots have a Parent UUID. >> >> Not all: >> >> root@xerus:/test# btrfs subvolume snapshot -r /test /test/ss1 >> Create a readonly snapshot of '/test' in '/test/ss1' >> >> root@xerus:/test# btrfs subvolume show /test/ss1 >> /test/ss1 >> Name: ss1 >> UUID: 02bd07bc-0bab-3442-96be-40790e1ba9be >> Parent UUID: - >> Received UUID: - >> Creation time: 2019-07-06 22:37:37 +0200 >> Subvolume ID: 1036 >> Generation: 9824 >> Gen at creation: 9824 >> Parent ID: 5 >> Top level ID: 5 >> Flags: readonly >> Snapshot(s): >> >> root@xerus:/test# btrfs subvolume show /test >> /test is toplevel subvolume > > This is really odd, looking at create_pending_snapshot the codes : > > memcpy(new_root_item->parent_uuid, root->root_item.uuid, > BTRFS_UUID_SIZE); > > And that's not conditional on whether the snapshot is read only or not. > So everytime we creata a snapshot it ought to be receiving the parent's > subvolume UUID in its parent_uuid field. Does top level subvolume of btrfs have subvolume UUID at all? How can one display it? None of "btrfs subvolume" commands show it. > And indeed testing with latest misc-next kernel: > > root@ubuntu-virtual:~# btrfs subvol create /media/scratch/subvol10 > Create subvolume '/media/scratch/subvol10' > > root@ubuntu-virtual:~# btrfs subvol snapshot /media/scratch/subvol10/ /media/scratch/snap-subvol10 > Create a snapshot of '/media/scratch/subvol10/' in '/media/scratch/snap-subvol10' > /media/scratch/subvol10 is not top level subvolume.
