xfs: fill out the srcmap in iomap_begin

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>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>

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);
 	}
 
 	/*
@@ -987,33 +990,18 @@ 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))
 			goto out_found;
 
 		/* 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;
 	}
@@ -1074,6 +1062,17 @@ 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;