[PATCH 2/8] xfs: move DIO mapping size calculation

[Brian Foster]

On Tue, Apr 14, 2015 at 05:26:45PM +1000, Dave Chinner wrote:
> From: Dave Chinner <dchinner at redhat.com>
> 
> The mapping size calculation is done last in __xfs_get_blocks(), but
> we are going to need the actual mapping size we will use to map the
> direct IO correctly in xfs_map_direct(). Factor out the calculation
> for code clarity, and move the call to be the first operation in
> mapping the extent to the returned buffer.
> 
> Signed-off-by: Dave Chinner <dchinner at redhat.com>
> ---

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

>  fs/xfs/xfs_aops.c | 79 ++++++++++++++++++++++++++++++++-----------------------
>  1 file changed, 46 insertions(+), 33 deletions(-)
> 
> diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c
> index 5f7ddd5..8f63520 100644
> --- a/fs/xfs/xfs_aops.c
> +++ b/fs/xfs/xfs_aops.c
> @@ -1249,6 +1249,47 @@ xfs_map_direct(
>  	}
>  }
>  
> +
> +/*
> + * If this is O_DIRECT or the mpage code calling tell them how large the mapping
> + * is, so that we can avoid repeated get_blocks calls.
> + *
> + * If the mapping spans EOF, then we have to break the mapping up as the mapping
> + * for blocks beyond EOF must be marked new so that sub block regions can be
> + * correctly zeroed. We can't do this for mappings within EOF unless the mapping
> + * was just allocated or is unwritten, otherwise the callers would overwrite
> + * existing data with zeros. Hence we have to split the mapping into a range up
> + * to and including EOF, and a second mapping for beyond EOF.
> + */
> +static void
> +xfs_map_trim_size(
> +	struct inode		*inode,
> +	sector_t		iblock,
> +	struct buffer_head	*bh_result,
> +	struct xfs_bmbt_irec	*imap,
> +	xfs_off_t		offset,
> +	ssize_t			size)
> +{
> +	xfs_off_t		mapping_size;
> +
> +	mapping_size = imap->br_startoff + imap->br_blockcount - iblock;
> +	mapping_size <<= inode->i_blkbits;
> +
> +	ASSERT(mapping_size > 0);
> +	if (mapping_size > size)
> +		mapping_size = size;
> +	if (offset < i_size_read(inode) &&
> +	    offset + mapping_size >= i_size_read(inode)) {
> +		/* limit mapping to block that spans EOF */
> +		mapping_size = roundup_64(i_size_read(inode) - offset,
> +					  1 << inode->i_blkbits);
> +	}
> +	if (mapping_size > LONG_MAX)
> +		mapping_size = LONG_MAX;
> +
> +	bh_result->b_size = mapping_size;
> +}
> +
>  STATIC int
>  __xfs_get_blocks(
>  	struct inode		*inode,
> @@ -1347,6 +1388,11 @@ __xfs_get_blocks(
>  		goto out_unlock;
>  	}
>  
> +	/* trim mapping down to size requested */
> +	if (direct || size > (1 << inode->i_blkbits))
> +		xfs_map_trim_size(inode, iblock, bh_result,
> +				  &imap, offset, size);
> +
>  	if (imap.br_startblock != HOLESTARTBLOCK &&
>  	    imap.br_startblock != DELAYSTARTBLOCK &&
>  	    (create || !ISUNWRITTEN(&imap))) {
> @@ -1388,39 +1434,6 @@ __xfs_get_blocks(
>  		}
>  	}
>  
> -	/*
> -	 * If this is O_DIRECT or the mpage code calling tell them how large
> -	 * the mapping is, so that we can avoid repeated get_blocks calls.
> -	 *
> -	 * If the mapping spans EOF, then we have to break the mapping up as the
> -	 * mapping for blocks beyond EOF must be marked new so that sub block
> -	 * regions can be correctly zeroed. We can't do this for mappings within
> -	 * EOF unless the mapping was just allocated or is unwritten, otherwise
> -	 * the callers would overwrite existing data with zeros. Hence we have
> -	 * to split the mapping into a range up to and including EOF, and a
> -	 * second mapping for beyond EOF.
> -	 */
> -	if (direct || size > (1 << inode->i_blkbits)) {
> -		xfs_off_t		mapping_size;
> -
> -		mapping_size = imap.br_startoff + imap.br_blockcount - iblock;
> -		mapping_size <<= inode->i_blkbits;
> -
> -		ASSERT(mapping_size > 0);
> -		if (mapping_size > size)
> -			mapping_size = size;
> -		if (offset < i_size_read(inode) &&
> -		    offset + mapping_size >= i_size_read(inode)) {
> -			/* limit mapping to block that spans EOF */
> -			mapping_size = roundup_64(i_size_read(inode) - offset,
> -						  1 << inode->i_blkbits);
> -		}
> -		if (mapping_size > LONG_MAX)
> -			mapping_size = LONG_MAX;
> -
> -		bh_result->b_size = mapping_size;
> -	}
> -
>  	return 0;
>  
>  out_unlock:
> -- 
> 2.0.0
> 
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