Re: [PATCH 13/20] xfs: fill out the srcmap in iomap_begin

From: "Darrick J. Wong" <darrick.wong@oracle.com>
To: Christoph Hellwig <hch@lst.de>
Cc: Goldwyn Rodrigues <rgoldwyn@suse.com>,
	linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH 13/20] xfs: fill out the srcmap in iomap_begin
Date: Tue, 8 Oct 2019 08:26:03 -0700	[thread overview]
Message-ID: <20191008152603.GZ13108@magnolia> (raw)
In-Reply-To: <20191008071527.29304-14-hch@lst.de>

On Tue, Oct 08, 2019 at 09:15:20AM +0200, Christoph Hellwig wrote:
> Replace our local hacks to report the source block in the main iomap
> with the proper scrmap reporting.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>

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

--D

> ---
>  fs/xfs/xfs_iomap.c | 49 +++++++++++++++++++++++-----------------------
>  1 file changed, 24 insertions(+), 25 deletions(-)
> 
> diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
> index 3292dfc8030a..ab2482a573d8 100644
> --- a/fs/xfs/xfs_iomap.c
> +++ b/fs/xfs/xfs_iomap.c
> @@ -527,7 +527,8 @@ xfs_file_iomap_begin_delay(
>  	loff_t			offset,
>  	loff_t			count,
>  	unsigned		flags,
> -	struct iomap		*iomap)
> +	struct iomap		*iomap,
> +	struct iomap		*srcmap)
>  {
>  	struct xfs_inode	*ip = XFS_I(inode);
>  	struct xfs_mount	*mp = ip->i_mount;
> @@ -721,11 +722,13 @@ xfs_file_iomap_begin_delay(
>  found_cow:
>  	xfs_iunlock(ip, XFS_ILOCK_EXCL);
>  	if (imap.br_startoff <= offset_fsb) {
> -		/* ensure we only report blocks we have a reservation for */
> -		xfs_trim_extent(&imap, cmap.br_startoff, cmap.br_blockcount);
> -		return xfs_bmbt_to_iomap(ip, iomap, &imap, IOMAP_F_SHARED);
> +		error = xfs_bmbt_to_iomap(ip, srcmap, &imap, 0);
> +		if (error)
> +			return error;
> +	} else {
> +		xfs_trim_extent(&cmap, offset_fsb,
> +				imap.br_startoff - offset_fsb);
>  	}
> -	xfs_trim_extent(&cmap, offset_fsb, imap.br_startoff - offset_fsb);
>  	return xfs_bmbt_to_iomap(ip, iomap, &cmap, IOMAP_F_SHARED);
>  
>  out_unlock:
> @@ -933,7 +936,7 @@ xfs_file_iomap_begin(
>  {
>  	struct xfs_inode	*ip = XFS_I(inode);
>  	struct xfs_mount	*mp = ip->i_mount;
> -	struct xfs_bmbt_irec	imap;
> +	struct xfs_bmbt_irec	imap, cmap;
>  	xfs_fileoff_t		offset_fsb, end_fsb;
>  	int			nimaps = 1, error = 0;
>  	bool			shared = false;
> @@ -947,7 +950,7 @@ xfs_file_iomap_begin(
>  			!IS_DAX(inode) && !xfs_get_extsz_hint(ip)) {
>  		/* Reserve delalloc blocks for regular writeback. */
>  		return xfs_file_iomap_begin_delay(inode, offset, length, flags,
> -				iomap);
> +				iomap, srcmap);
>  	}
>  
>  	/*
> @@ -987,9 +990,6 @@ xfs_file_iomap_begin(
>  	 * been done up front, so we don't need to do them here.
>  	 */
>  	if (xfs_is_cow_inode(ip)) {
> -		struct xfs_bmbt_irec	cmap;
> -		bool			directio = (flags & IOMAP_DIRECT);
> -
>  		/* if zeroing doesn't need COW allocation, then we are done. */
>  		if ((flags & IOMAP_ZERO) &&
>  		    !needs_cow_for_zeroing(&imap, nimaps))
> @@ -997,23 +997,11 @@ xfs_file_iomap_begin(
>  
>  		/* may drop and re-acquire the ilock */
>  		error = xfs_reflink_allocate_cow(ip, &imap, &cmap, &shared,
> -				&lockmode, directio);
> +				&lockmode, flags & IOMAP_DIRECT);
>  		if (error)
>  			goto out_unlock;
> -
> -		/*
> -		 * For buffered writes we need to report the address of the
> -		 * previous block (if there was any) so that the higher level
> -		 * write code can perform read-modify-write operations; we
> -		 * won't need the CoW fork mapping until writeback.  For direct
> -		 * I/O, which must be block aligned, we need to report the
> -		 * newly allocated address.  If the data fork has a hole, copy
> -		 * the COW fork mapping to avoid allocating to the data fork.
> -		 */
> -		if (shared &&
> -		    (directio || imap.br_startblock == HOLESTARTBLOCK))
> -			imap = cmap;
> -
> +		if (shared)
> +			goto out_found_cow;
>  		end_fsb = imap.br_startoff + imap.br_blockcount;
>  		length = XFS_FSB_TO_B(mp, end_fsb) - offset;
>  	}
> @@ -1067,6 +1055,17 @@ xfs_file_iomap_begin(
>  	trace_xfs_iomap_found(ip, offset, length, XFS_DATA_FORK, &imap);
>  	goto out_finish;
>  
> +out_found_cow:
> +	xfs_iunlock(ip, lockmode);
> +	length = XFS_FSB_TO_B(mp, cmap.br_startoff + cmap.br_blockcount);
> +	trace_xfs_iomap_found(ip, offset, length - offset, XFS_COW_FORK, &cmap);
> +	if (imap.br_startblock != HOLESTARTBLOCK) {
> +		error = xfs_bmbt_to_iomap(ip, srcmap, &imap, 0);
> +		if (error)
> +			return error;
> +	}
> +	return xfs_bmbt_to_iomap(ip, iomap, &cmap, IOMAP_F_SHARED);
> +
>  out_unlock:
>  	xfs_iunlock(ip, lockmode);
>  	return error;
> -- 
> 2.20.1
> 