xfs: introduce xfs_aligned_fsb_count

Factor a helper to calculate the extent-size aligned block out of the
iomap code, so that it can be reused by the upcoming reflink dio code.

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

@@ -162,7 +162,7 @@ xfs_iomap_write_direct(
 	xfs_fileoff_t	last_fsb;
 	xfs_filblks_t	count_fsb, resaligned;
 	xfs_fsblock_t	firstfsb;
-	xfs_extlen_t	extsz, temp;
+	xfs_extlen_t	extsz;
 	int		nimaps;
 	int		quota_flag;
 	int		rt;
@@ -203,14 +203,7 @@ xfs_iomap_write_direct(
 	}
 	count_fsb = last_fsb - offset_fsb;
 	ASSERT(count_fsb > 0);
-
-	resaligned = count_fsb;
-	if (unlikely(extsz)) {
-		if ((temp = do_mod(offset_fsb, extsz)))
-			resaligned += temp;
-		if ((temp = do_mod(resaligned, extsz)))
-			resaligned += extsz - temp;
-	}
+	resaligned = xfs_aligned_fsb_count(offset_fsb, count_fsb, extsz);
 
 	if (unlikely(rt)) {
 		resrtextents = qblocks = resaligned;

fs/xfs/xfs_iomap.h

@@ -33,6 +33,26 @@ void xfs_bmbt_to_iomap(struct xfs_inode *, struct iomap *,
 		struct xfs_bmbt_irec *);
 xfs_extlen_t xfs_eof_alignment(struct xfs_inode *ip, xfs_extlen_t extsize);
 
+static inline xfs_filblks_t
+xfs_aligned_fsb_count(
+	xfs_fileoff_t		offset_fsb,
+	xfs_filblks_t		count_fsb,
+	xfs_extlen_t		extsz)
+{
+	if (extsz) {
+		xfs_extlen_t	align;
+
+		align = do_mod(offset_fsb, extsz);
+		if (align)
+			count_fsb += align;
+		align = do_mod(count_fsb, extsz);
+		if (align)
+			count_fsb += extsz - align;
+	}
+
+	return count_fsb;
+}
+
 extern const struct iomap_ops xfs_iomap_ops;
 extern const struct iomap_ops xfs_xattr_iomap_ops;