Re: [PATCH] xfs_repair: refuse to unset lazycount on V5 filesystems

[Brian Foster <bfoster@redhat.com>]

On Thu, Jun 18, 2015 at 12:01:22PM -0500, Eric Sandeen wrote:
> Running "xfs_admin -c 0" on a V5 fs has unfortunate results.
> 
> Before:
> versionnum [0xbca5+0x18a] = ... LAZYSBCOUNT,PROJID32BIT,CRC, ...
> After:
> versionnum [0xbca5+0x188] = ... LAZYSBCOUNT,PROJID32BIT,CRC, ...
> 
> The on-disk feature bit is in fact changed, but xfs_db reports that the
> feature is still present.  This is because xfs_sb_version_haslazysbcount()
> ignores the feature bit, and always reports that the lazy-count feature is
> present on a V5 fs.
> 
> i.e. the intent is that this feature is not optional on a V5 fs, yet we
> still flip the bit on disk when asked.  Not good.
> 
> So, document this, and error out if the user tries to disable lazy-count
> on a version 5 filesystem.
> 
> Reported-by: Richard W.M. Jones <rjones@redhat.com>
> Signed-off-by: Eric Sandeen <sandeen@redhat.com>
> ---

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

> 
> (hm, xfs_repair should probably also turn the bit back on, if it's off on
> V5?  I'll save that for another patch.)
> 

Seems reasonable.

Brian

> diff --git a/man/man8/xfs_admin.8 b/man/man8/xfs_admin.8
> index b393d74..0968196 100644
> --- a/man/man8/xfs_admin.8
> +++ b/man/man8/xfs_admin.8
> @@ -62,6 +62,10 @@ Print the current filesystem UUID (Universally Unique IDentifier).
>  .TP
>  .BR "\-c 0" | 1
>  Enable (1) or disable (0) lazy-counters in the filesystem.
> +.IP
> +Lazy-counters may not be disabled on Version 5 superblock filesystems
> +(i.e. those with metadata CRCs enabled).
> +.IP
>  This operation may take quite a bit of time on large filesystems as the
>  entire filesystem needs to be scanned when this option is changed.
>  .IP
> 
> diff --git a/repair/phase1.c b/repair/phase1.c
> index ec75ada..9e7011d 100644
> --- a/repair/phase1.c
> +++ b/repair/phase1.c
> @@ -121,8 +121,12 @@ phase1(xfs_mount_t *mp)
>  			sb->sb_bad_features2 |= XFS_SB_VERSION2_LAZYSBCOUNTBIT;
>  			primary_sb_modified = 1;
>  			printf(_("Enabling lazy-counters\n"));
> -		} else
> -		if (!lazy_count && xfs_sb_version_haslazysbcount(sb)) {
> +		} else if (!lazy_count && xfs_sb_version_haslazysbcount(sb)) {
> +			if (XFS_SB_VERSION_NUM(sb) == XFS_SB_VERSION_5) {
> +				printf(
> +_("Cannot disable lazy-counters on V5 fs\n"));
> +				exit(1);
> +			}
>  			sb->sb_features2 &= ~XFS_SB_VERSION2_LAZYSBCOUNTBIT;
>  			sb->sb_bad_features2 &= ~XFS_SB_VERSION2_LAZYSBCOUNTBIT;
>  			printf(_("Disabling lazy-counters\n"));
> 
> 
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