Re: [PATCH 2/9] xfs: improve the xfs_dabuf_map calling conventions

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

On Sat, Nov 16, 2019 at 07:22:07PM +0100, Christoph Hellwig wrote:
> Use a flags argument with the XFS_DABUF_MAP_HOLE_OK flag to signal that
> a hole is okay and not corruption, and return -ENOENT instead of the
> nameless -1 to signal that case in the return value.

Why not set *nirecs = 0 and return 0 like we sometimes do for bmap
lookups?

--D

> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  fs/xfs/libxfs/xfs_da_btree.c | 25 +++++++++++++++----------
>  fs/xfs/libxfs/xfs_da_btree.h |  3 +++
>  2 files changed, 18 insertions(+), 10 deletions(-)
> 
> diff --git a/fs/xfs/libxfs/xfs_da_btree.c b/fs/xfs/libxfs/xfs_da_btree.c
> index 681fba5731c2..c26f139bcf00 100644
> --- a/fs/xfs/libxfs/xfs_da_btree.c
> +++ b/fs/xfs/libxfs/xfs_da_btree.c
> @@ -2571,7 +2571,7 @@ static int
>  xfs_dabuf_map(
>  	struct xfs_inode	*dp,
>  	xfs_dablk_t		bno,
> -	xfs_daddr_t		mappedbno,
> +	unsigned int		flags,
>  	int			whichfork,
>  	struct xfs_buf_map	**map,
>  	int			*nmaps)
> @@ -2596,8 +2596,8 @@ xfs_dabuf_map(
>  
>  	if (!xfs_da_map_covers_blocks(nirecs, irecs, bno, nfsb)) {
>  		/* Caller ok with no mapping. */
> -		if (mappedbno == -2) {
> -			error = -1;
> +		if (flags & XFS_DABUF_MAP_HOLE_OK) {
> +			error = -ENOENT;
>  			goto out;
>  		}
>  
> @@ -2655,10 +2655,12 @@ xfs_da_get_buf(
>  		goto done;
>  	}
>  
> -	error = xfs_dabuf_map(dp, bno, mappedbno, whichfork, &mapp, &nmap);
> +	error = xfs_dabuf_map(dp, bno,
> +			mappedbno == -1 ? XFS_DABUF_MAP_HOLE_OK : 0,
> +			whichfork, &mapp, &nmap);
>  	if (error) {
>  		/* mapping a hole is not an error, but we don't continue */
> -		if (error == -1)
> +		if (error == -ENOENT)
>  			error = 0;
>  		goto out_free;
>  	}
> @@ -2710,10 +2712,12 @@ xfs_da_read_buf(
>  		goto done;
>  	}
>  
> -	error = xfs_dabuf_map(dp, bno, mappedbno, whichfork, &mapp, &nmap);
> +	error = xfs_dabuf_map(dp, bno,
> +			mappedbno == -1 ? XFS_DABUF_MAP_HOLE_OK : 0,
> +			whichfork, &mapp, &nmap);
>  	if (error) {
>  		/* mapping a hole is not an error, but we don't continue */
> -		if (error == -1)
> +		if (error == -ENOENT)
>  			error = 0;
>  		goto out_free;
>  	}
> @@ -2757,11 +2761,12 @@ xfs_da_reada_buf(
>  
>  	mapp = &map;
>  	nmap = 1;
> -	error = xfs_dabuf_map(dp, bno, mappedbno, whichfork,
> -				&mapp, &nmap);
> +	error = xfs_dabuf_map(dp, bno,
> +			mappedbno == -1 ? XFS_DABUF_MAP_HOLE_OK : 0,
> +			whichfork, &mapp, &nmap);
>  	if (error) {
>  		/* mapping a hole is not an error, but we don't continue */
> -		if (error == -1)
> +		if (error == -ENOENT)
>  			error = 0;
>  		goto out_free;
>  	}
> diff --git a/fs/xfs/libxfs/xfs_da_btree.h b/fs/xfs/libxfs/xfs_da_btree.h
> index 5af4df71e92b..9ec0d0243e96 100644
> --- a/fs/xfs/libxfs/xfs_da_btree.h
> +++ b/fs/xfs/libxfs/xfs_da_btree.h
> @@ -204,6 +204,9 @@ int	xfs_da3_node_read(struct xfs_trans *tp, struct xfs_inode *dp,
>  /*
>   * Utility routines.
>   */
> +
> +#define XFS_DABUF_MAP_HOLE_OK	(1 << 0)
> +
>  int	xfs_da_grow_inode(xfs_da_args_t *args, xfs_dablk_t *new_blkno);
>  int	xfs_da_grow_inode_int(struct xfs_da_args *args, xfs_fileoff_t *bno,
>  			      int count);
> -- 
> 2.20.1
>