Btrfs devel - Sep 2012 - [PATCH] btrfs: fix disk-io.c/btrfs_read_dev_super with BTRFS_SUPER_MIRROR_MAX to control the loops

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;
-- 
1.7.1

On Mon, Sep 10, 2012 at 12:38 AM, Wang Sheng-Hui <shhuiw@gmail.com>
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;
> --
> 1.7.1
>
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Please fix the comment as well; if we check all the supers, then
mounting as btrfs _will_ succeed after a different (non-btrfs)
filesystem is created on the partition/device, pretty much
guaranteeing it will be corrupted.

On Mon, Sep 10, 2012 at 12:38:35AM -0600, 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;
We don''t want to do this, it should be left for -o recovery or some
such mount
option.  Thanks,

Josef

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




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