linux-kernel - Re: [PATCH] btrfs: fix disk-io.c/btrfs_read_dev_super with BTRFS_SUPER_MIRROR

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Message-ID: <504EC8BA.7010706@libero.it>
Date:	Tue, 11 Sep 2012 07:14:34 +0200
From:	Goffredo Baroncelli <kreijack@...ero.it>
To:	Wang Sheng-Hui <shhuiw@...il.com>
CC:	chris.mason@...ionio.com, linux-btrfs@...r.kernel.org,
	linux-kernel@...r.kernel.org, cwillu <cwillu@...llu.com>,
	Josef Bacik <jbacik@...ionio.com>
Subject: Re: [PATCH] btrfs: fix disk-io.c/btrfs_read_dev_super with BTRFS_SUPER_MIRROR_MAX
 to control the loops

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@...il.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




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