On 7/10/20 2:37 AM, Anand Jain wrote:
->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 messy. 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 Signed-off-by: Anand Jain <anand.jain@xxxxxxxxxx>
This needs to come with an xfstest so we do not regress this in the future. Thanks, Josef
