Re: [PATCH] btrfs: init device stats for seed devices

[David Sterba <dsterba@suse.cz>]

On Mon, Aug 03, 2020 at 03:23:08PM -0400, Josef Bacik wrote:
> We recently started recording device stats across the fleet, and noticed
> a large increase in messages such as this
> 
> BTRFS warning (device dm-0): get dev_stats failed, not yet valid
> 
> on our tiers that use seed devices for their root devices.  This is
> because we do not initialize the device stats for any seed devices if we
> have a sprout device and mount using that sprout device.  The basic
> steps for reproducing are
> 
> mkfs seed device
> mount seed device
> fill seed device
> umount seed device
> btrfstune -S 1 seed device
> mount seed device
> btrfs device add -f sprout device /mnt/wherever
> umount /mnt/wherever
> mount sprout device /mnt/wherever
> btrfs device stats /mnt/wherever
> 
> This will fail with the above message in dmesg.
> 
> Fix this by iterating over the fs_devices->seed if they exist in
> btrfs_init_dev_stats.  This fixed the problem and properly reports the
> stats for both devices.
> 
> Signed-off-by: Josef Bacik <josef@toxicpanda.com>

Please update the patch after the device list api changes, thanks.