Re: [PATCH] btrfs: fix disk-io.c/btrfs_read_dev_super with BTRFS_SUPER_MIRROR_MAX to control the loops

Goffredo Baroncelli
2012-09-11T05:19:20Z

Hi,

On 09/10/2012 08:38 AM, Wang Sheng-Hui wrote:
> To check the duplicated super blocks, use BTRFS_SUPER_MIRROR_MAX
> as the loops limit.
>
> Signed-off-by: Wang Sheng-Hui<shhuiw@gmail.com>
> ---
> fs/btrfs/disk-io.c | 2 +-
> 1 files changed, 1 insertions(+), 1 deletions(-)
>
> diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
> index 22e98e0..a431144 100644
> --- a/fs/btrfs/disk-io.c
> +++ b/fs/btrfs/disk-io.c
> @@ -2723,7 +2723,7 @@ struct buffer_head *btrfs_read_dev_super(struct block_device *bdev)
> * So, we need to add a special mount option to scan for
> * later supers, using BTRFS_SUPER_MIRROR_MAX instead
> */
> - for (i = 0; i< 1; i++) {
> + for (i = 0; i< BTRFS_SUPER_MIRROR_MAX; i++) {
> bytenr = btrfs_sb_offset(i);
> if (bytenr + 4096>= i_size_read(bdev->bd_inode))
> break;

Pay attention that when a device is removed from a filesystem by the
command "btrfs device delete", *only* the 1st superblock btrfs signature
is zeroed [1]. This means that the other (backup) superblocks will be
considered valid with your change.

[1] See the function btrfs_rm_device() in volume.c