btrfs: don't traverse into the seed devices in show_devname
->show_devname currently shows the lowest devid in the list. As the seed
devices have the lowest devid in the sprouted filesystem, the userland
tool such as findmnt end up seeing seed device instead of the device from
the read-writable sprouted filesystem. As shown below.
mount /dev/sda /btrfs
mount: /btrfs: WARNING: device write-protected, mounted read-only.
findmnt --output SOURCE,TARGET,UUID /btrfs
SOURCE TARGET UUID
/dev/sda /btrfs
899f7027-3e46-4626-93e7-
7d4c9ad19111
btrfs dev add -f /dev/sdb /btrfs
umount /btrfs
mount /dev/sdb /btrfs
findmnt --output SOURCE,TARGET,UUID /btrfs
SOURCE TARGET UUID
/dev/sda /btrfs
899f7027-3e46-4626-93e7-
7d4c9ad19111
All sprouts from a single seed will show the same seed device and the
same fsid. That's confusing.
This is causing problems in our prototype as there isn't any reference
to the sprout file-system(s) which is being used for actual read and
write.
This was added in the patch which implemented the show_devname in btrfs
commit
9c5085c14798 ("Btrfs: implement ->show_devname").
I tried to look for any particular reason that we need to show the seed
device, there isn't any.
So instead, do not traverse through the seed devices, just show the
lowest devid in the sprouted fsid.
After the patch:
mount /dev/sda /btrfs
mount: /btrfs: WARNING: device write-protected, mounted read-only.
findmnt --output SOURCE,TARGET,UUID /btrfs
SOURCE TARGET UUID
/dev/sda /btrfs
899f7027-3e46-4626-93e7-
7d4c9ad19111
btrfs dev add -f /dev/sdb /btrfs
mount -o rw,remount /dev/sdb /btrfs
findmnt --output SOURCE,TARGET,UUID /btrfs
SOURCE TARGET UUID
/dev/sdb /btrfs
595ca0e6-b82e-46b5-b9e2-
c72a6928be48
mount /dev/sda /btrfs1
mount: /btrfs1: WARNING: device write-protected, mounted read-only.
btrfs dev add -f /dev/sdc /btrfs1
findmnt --output SOURCE,TARGET,UUID /btrfs1
SOURCE TARGET UUID
/dev/sdc /btrfs1
ca1dbb7a-8446-4f95-853c-
a20f3f82bdbb
cat /proc/self/mounts | grep btrfs
/dev/sdb /btrfs btrfs rw,relatime,noacl,space_cache,subvolid=5,subvol=/ 0 0
/dev/sdc /btrfs1 btrfs ro,relatime,noacl,space_cache,subvolid=5,subvol=/ 0 0
Reported-by: Martin K. Petersen <martin.petersen@oracle.com>
CC: stable@vger.kernel.org # 4.19+
Tested-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Anand Jain <anand.jain@oracle.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>