Re: [PATCH 01/25] xfs: allow null firstblock in xfs_bmapi_write() when tp is null

["Darrick J. Wong" <darrick.wong@oracle.com>]

On Tue, Jul 03, 2018 at 01:22:55PM -0400, Brian Foster wrote:
> xfs_bmapi_write() always expects a valid firstblock pointer. It
> immediately dereferences the pointer to help determine how to
> initialize the bma.minleft field. The remaining accesses are
> related to modifying btree format forks, which is only relevant for
> !COW fork callers.
> 
> The reflink code passes a NULL transaction to xfs_bmapi_write() in a
> couple places that do COW fork unwritten conversion. The purpose of
> the firstblock field is to track the first block allocation in the
> current transaction, so technically firstblock should not be
> required for these callers either.
> 
> Tweak xfs_bmapi_write() to initialize the bma correctly without
> accessing the firstblock pointer if no transaction is provided in
> the first place. Update the reflink callers to pass NULL instead of
> otherwise unused firstblock references.
> 
> Signed-off-by: Brian Foster <bfoster@redhat.com>

Looks ok,
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>

--D

> ---
>  fs/xfs/libxfs/xfs_bmap.c | 2 +-
>  fs/xfs/xfs_reflink.c     | 9 +++------
>  2 files changed, 4 insertions(+), 7 deletions(-)
> 
> diff --git a/fs/xfs/libxfs/xfs_bmap.c b/fs/xfs/libxfs/xfs_bmap.c
> index 2e2a9661600b..c6a5a957674d 100644
> --- a/fs/xfs/libxfs/xfs_bmap.c
> +++ b/fs/xfs/libxfs/xfs_bmap.c
> @@ -4304,7 +4304,7 @@ xfs_bmapi_write(
>  
>  	XFS_STATS_INC(mp, xs_blk_mapw);
>  
> -	if (*firstblock == NULLFSBLOCK) {
> +	if (!tp || *firstblock == NULLFSBLOCK) {
>  		if (XFS_IFORK_FORMAT(ip, whichfork) == XFS_DINODE_FMT_BTREE)
>  			bma.minleft = be16_to_cpu(ifp->if_broot->bb_level) + 1;
>  		else
> diff --git a/fs/xfs/xfs_reflink.c b/fs/xfs/xfs_reflink.c
> index 8496312dde6a..92b6e1b5d33c 100644
> --- a/fs/xfs/xfs_reflink.c
> +++ b/fs/xfs/xfs_reflink.c
> @@ -314,7 +314,6 @@ xfs_reflink_convert_cow_extent(
>  	xfs_fileoff_t			offset_fsb,
>  	xfs_filblks_t			count_fsb)
>  {
> -	xfs_fsblock_t			first_block = NULLFSBLOCK;
>  	int				nimaps = 1;
>  
>  	if (imap->br_state == XFS_EXT_NORM)
> @@ -325,8 +324,8 @@ xfs_reflink_convert_cow_extent(
>  	if (imap->br_blockcount == 0)
>  		return 0;
>  	return xfs_bmapi_write(NULL, ip, imap->br_startoff, imap->br_blockcount,
> -			XFS_BMAPI_COWFORK | XFS_BMAPI_CONVERT, &first_block,
> -			0, imap, &nimaps);
> +			XFS_BMAPI_COWFORK | XFS_BMAPI_CONVERT, NULL, 0, imap,
> +			&nimaps);
>  }
>  
>  /* Convert all of the unwritten CoW extents in a file's range to real ones. */
> @@ -341,7 +340,6 @@ xfs_reflink_convert_cow(
>  	xfs_fileoff_t		end_fsb = XFS_B_TO_FSB(mp, offset + count);
>  	xfs_filblks_t		count_fsb = end_fsb - offset_fsb;
>  	struct xfs_bmbt_irec	imap;
> -	xfs_fsblock_t		first_block = NULLFSBLOCK;
>  	int			nimaps = 1, error = 0;
>  
>  	ASSERT(count != 0);
> @@ -349,8 +347,7 @@ xfs_reflink_convert_cow(
>  	xfs_ilock(ip, XFS_ILOCK_EXCL);
>  	error = xfs_bmapi_write(NULL, ip, offset_fsb, count_fsb,
>  			XFS_BMAPI_COWFORK | XFS_BMAPI_CONVERT |
> -			XFS_BMAPI_CONVERT_ONLY, &first_block, 0, &imap,
> -			&nimaps);
> +			XFS_BMAPI_CONVERT_ONLY, NULL, 0, &imap, &nimaps);
>  	xfs_iunlock(ip, XFS_ILOCK_EXCL);
>  	return error;
>  }
> -- 
> 2.17.1
> 
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