Bug#782012: [PATCH] xfs_db: disallow sb UUID write on v5 filesystems

[Brian Foster]

On Mon, Apr 06, 2015 at 10:06:03AM -0500, Eric Sandeen wrote:
> Do not allow xfs_db (or the xfs_admin frontend) to change the UUID
> of a V5 filesystem; this will cause UUID mismatches across the
> filesystem, and we currently have no mechanism to update them all.
> Changing only the superblock UUID makes all other metadata look
> invalid, and xfs_repair reacts by junking everything.
> 
> Addresses-Debian-Bug: 782012
> Reported-by: F. Stoyan <fstoyan at swapon.de>
> Signed-off-by: Eric Sandeen <sandeen at redhat.com>
> ---
> 
> diff --git a/db/sb.c b/db/sb.c
> index 6cb665d..f31f4a2 100644
> --- a/db/sb.c
> +++ b/db/sb.c
> @@ -363,6 +363,18 @@ uuid_f(
>  			return 0;
>  		}
>  
> +		/*
> +		* For now, changing the UUID of V5 superblock filesystems is
> +		* not supported; we do not have the infrastructure to fix all
> +		* other metadata when a new superblock UUID is generated.
> +		*/

Unaligned start of comment above. :) Otherwise looks fine to me:

Reviewed-by: Brian Foster <bfoster at redhat.com>

> +		if (xfs_sb_version_hascrc(&mp->m_sb) &&
> +		    strcasecmp(argv[1], "rewrite")) {
> +			dbprintf(_("%s: only 'rewrite' supported on V5 fs\n"),
> +				progname);
> +			return 0;
> +		}
> +
>  		if (!strcasecmp(argv[1], "generate")) {
>  			platform_uuid_generate(&uu);
>  		} else if (!strcasecmp(argv[1], "nil")) {
> 
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