Re: [PATCH] Btrfs: set right total device count for seeding support

[Anand Jain <Anand.Jain@oracle.com>]

Wang,

  There seems to be a problem - after we delete the seed
  disk, the total_devices didn't decrement back to 1.
  reproducer as in the below test case. (I used btrfs-devlist
  (posted) to check fs_devices).

  > # mkfs.btrfs -f /dev/sdb
  > # btrfstune -S 1 /dev/sdb
  > # mount /dev/sdb /mnt
  > # btrfs device add -f /dev/sdc /mnt --->fs_devices->total_devices = 1
  mount -o rw,remount /mnt
  btrfs dev del /dev/sdb /mnt --> fs_devices->total_devices is still 2

Thanks, Anand


On 13/05/14 17:05, Wang Shilong wrote:
> Seeding device support allows us to create a new filesystem
> based on existed filesystem.
>
> However newly created filesystem's @total_devices should include seed
> devices. This patch fix the following problem:
>
>   # mkfs.btrfs -f /dev/sdb
>   # btrfstune -S 1 /dev/sdb
>   # mount /dev/sdb /mnt
>   # btrfs device add -f /dev/sdc /mnt --->fs_devices->total_devices = 1
>   # umount /mnt
>   # mount /dev/sdc /mnt               --->fs_devices->total_devices = 2
>
> This is because we record right @total_devices in superblock, but
> @fs_devices->total_devices is reset to be 0 in btrfs_prepare_sprout().
>
> Fix this problem by not resetting @fs_devices->total_devices.
>
> Signed-off-by: Wang Shilong <wangsl.fnst@cn.fujitsu.com>
> ---
>   fs/btrfs/volumes.c | 1 -
>   1 file changed, 1 deletion(-)
>
> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
> index 6fd7fe6..19b2d32 100644
> --- a/fs/btrfs/volumes.c
> +++ b/fs/btrfs/volumes.c
> @@ -1883,7 +1883,6 @@ static int btrfs_prepare_sprout(struct btrfs_root *root)
>   	fs_devices->seeding = 0;
>   	fs_devices->num_devices = 0;
>   	fs_devices->open_devices = 0;
> -	fs_devices->total_devices = 0;
>   	fs_devices->seed = seed_devices;
>
>   	generate_random_uuid(fs_devices->fsid);
>