Re: [PATCH 09/10] xfs: validate feature support when recovering rmap/refcount/bmap intents

From: Brian Foster <bfoster@redhat.com>
To: "Darrick J. Wong" <darrick.wong@oracle.com>
Cc: Christoph Hellwig <hch@lst.de>, linux-xfs@vger.kernel.org
Subject: Re: [PATCH 09/10] xfs: validate feature support when recovering rmap/refcount/bmap intents
Date: Fri, 4 Dec 2020 09:00:36 -0500	[thread overview]
Message-ID: <20201204140036.GK1404170@bfoster> (raw)
In-Reply-To: <160704435080.734470.11175993745850698818.stgit@magnolia>

On Thu, Dec 03, 2020 at 05:12:30PM -0800, Darrick J. Wong wrote:
> From: Darrick J. Wong <darrick.wong@oracle.com>
> 
> The bmap, rmap, and refcount log intent items were added to support the
> rmap and reflink features.  Because these features come with changes to
> the ondisk format, the log items aren't tied to a log incompat flag.
> 
> However, the log recovery routines don't actually check for those
> feature flags.  The kernel has no business replayng an intent item for a
> feature that isn't enabled, so check that as part of recovered log item
> validation.  (Note that kernels pre-dating rmap and reflink will fail
> the mount on the unknown log item type code.)
> 
> Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> Reviewed-by: Christoph Hellwig <hch@lst.de>
> ---
>  fs/xfs/xfs_bmap_item.c     |    4 ++++
>  fs/xfs/xfs_refcount_item.c |    3 +++
>  fs/xfs/xfs_rmap_item.c     |    3 +++
>  3 files changed, 10 insertions(+)
> 
> 
> diff --git a/fs/xfs/xfs_bmap_item.c b/fs/xfs/xfs_bmap_item.c
> index 78346d47564b..4ea9132716c6 100644
> --- a/fs/xfs/xfs_bmap_item.c
> +++ b/fs/xfs/xfs_bmap_item.c
> @@ -425,6 +425,10 @@ xfs_bui_validate(
>  {
>  	struct xfs_map_extent		*bmap;
>  
> +	if (!xfs_sb_version_hasrmapbt(&mp->m_sb) &&
> +	    !xfs_sb_version_hasreflink(&mp->m_sb))
> +		return false;
> +

Took me a minute to realize we use the map/unmap for extent swap if rmap
is enabled. That does make me wonder a bit.. had we made this kind of
recovery feature validation change before that came around (such that we
probably would have only checked _hasreflink() here), would we have
created an unnecessary backwards incompatibility?

Brian

>  	/* Only one mapping operation per BUI... */
>  	if (buip->bui_format.bui_nextents != XFS_BUI_MAX_FAST_EXTENTS)
>  		return false;
> diff --git a/fs/xfs/xfs_refcount_item.c b/fs/xfs/xfs_refcount_item.c
> index 8ad6c81f6d8f..2b28f5643c0b 100644
> --- a/fs/xfs/xfs_refcount_item.c
> +++ b/fs/xfs/xfs_refcount_item.c
> @@ -423,6 +423,9 @@ xfs_cui_validate_phys(
>  	struct xfs_mount		*mp,
>  	struct xfs_phys_extent		*refc)
>  {
> +	if (!xfs_sb_version_hasreflink(&mp->m_sb))
> +		return false;
> +
>  	if (refc->pe_flags & ~XFS_REFCOUNT_EXTENT_FLAGS)
>  		return false;
>  
> diff --git a/fs/xfs/xfs_rmap_item.c b/fs/xfs/xfs_rmap_item.c
> index f296ec349936..2628bc0080fe 100644
> --- a/fs/xfs/xfs_rmap_item.c
> +++ b/fs/xfs/xfs_rmap_item.c
> @@ -466,6 +466,9 @@ xfs_rui_validate_map(
>  	struct xfs_mount		*mp,
>  	struct xfs_map_extent		*rmap)
>  {
> +	if (!xfs_sb_version_hasrmapbt(&mp->m_sb))
> +		return false;
> +
>  	if (rmap->me_flags & ~XFS_RMAP_EXTENT_FLAGS)
>  		return false;
>  
> 