Re: [PATCH 03/10] xfs: improve the xfs_dabuf_map calling conventions

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

On Wed, Nov 20, 2019 at 12:17:20PM +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 0 with *nmap set to 0 to
> signal that case in the return value instead of a nameless -1 return
> code.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  fs/xfs/libxfs/xfs_da_btree.c | 39 +++++++++++++-----------------------
>  fs/xfs/libxfs/xfs_da_btree.h |  3 +++
>  2 files changed, 17 insertions(+), 25 deletions(-)
> 
> diff --git a/fs/xfs/libxfs/xfs_da_btree.c b/fs/xfs/libxfs/xfs_da_btree.c
> index e078817fc26c..d85dd99d28a3 100644
> --- a/fs/xfs/libxfs/xfs_da_btree.c
> +++ b/fs/xfs/libxfs/xfs_da_btree.c
> @@ -2460,19 +2460,11 @@ xfs_da_shrink_inode(
>  	return error;
>  }
>  
> -/*
> - * Map the block we are given ready for reading. There are three possible return
> - * values:
> - *	-1 - will be returned if we land in a hole and mappedbno == -2 so the
> - *	     caller knows not to execute a subsequent read.
> - *	 0 - if we mapped the block successfully
> - *	>0 - positive error number if there was an error.
> - */
>  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	**mapp,
>  	int			*nmaps)
> @@ -2527,7 +2519,7 @@ xfs_dabuf_map(
>  
>  invalid_mapping:
>  	/* Caller ok with no mapping. */
> -	if (XFS_IS_CORRUPT(mp, mappedbno != -2)) {
> +	if (XFS_IS_CORRUPT(mp, !flags & XFS_DABUF_MAP_HOLE_OK)) {

Also I totally forgot to mention this flags test ^^^^^^^^ probably
should have parentheses...

--D

>  		error = -EFSCORRUPTED;
>  		if (xfs_error_level >= XFS_ERRLEVEL_LOW) {
>  			xfs_alert(mp, "%s: bno %u inode %llu",
> @@ -2575,13 +2567,11 @@ xfs_da_get_buf(
>  		goto done;
>  	}
>  
> -	error = xfs_dabuf_map(dp, bno, mappedbno, whichfork, &mapp, &nmap);
> -	if (error) {
> -		/* mapping a hole is not an error, but we don't continue */
> -		if (error == -1)
> -			error = 0;
> +	error = xfs_dabuf_map(dp, bno,
> +			mappedbno == -1 ? XFS_DABUF_MAP_HOLE_OK : 0,
> +			whichfork, &mapp, &nmap);
> +	if (error || nmap == 0)
>  		goto out_free;
> -	}
>  
>  	bp = xfs_trans_get_buf_map(tp, mp->m_ddev_targp, mapp, nmap, 0);
>  done:
> @@ -2630,13 +2620,11 @@ xfs_da_read_buf(
>  		goto done;
>  	}
>  
> -	error = xfs_dabuf_map(dp, bno, mappedbno, whichfork, &mapp, &nmap);
> -	if (error) {
> -		/* mapping a hole is not an error, but we don't continue */
> -		if (error == -1)
> -			error = 0;
> +	error = xfs_dabuf_map(dp, bno,
> +			mappedbno == -1 ? XFS_DABUF_MAP_HOLE_OK : 0,
> +			whichfork, &mapp, &nmap);
> +	if (error || !nmap)
>  		goto out_free;
> -	}
>  
>  	error = xfs_trans_read_buf_map(mp, tp, mp->m_ddev_targp, mapp, nmap, 0,
>  			&bp, ops);
> @@ -2677,11 +2665,12 @@ 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 ed3b558a9c1a..64624d5717c9 100644
> --- a/fs/xfs/libxfs/xfs_da_btree.h
> +++ b/fs/xfs/libxfs/xfs_da_btree.h
> @@ -194,6 +194,9 @@ 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
>