[PATCH v3 3/3] xfs: introduce xfs_bremapi_from_cowfork()

[Gao Xiang]

Previously, xfs_reflink_end_cow_extent() will unconditionally unmap
the corresponding old extent and remap an extent from COW fork.
However, it seems somewhat ineffective since the old bmbt records can
be directly updated for many cases instead.

This patch uses introduced xfs_bmap_update_extent_real() in the
previous patch for most extent inclusive cases or it will fall back
to the old way if such replacement is not possible.

Actually, we're planing to use a modified alway-cow like atomic write
approach internally, therefore it'd be nice to do some optimization
to reduce some metadata overhead.

Signed-off-by: Gao Xiang <hsiangkao@xxxxxxxxxxxxxxxxx>
---
changes since v2:
 - fix quota accounting found by tests which were not run by mistake;
   Also, after this patch, xfs/312 will be false positive since
   xfs_bmap_finish_one() can be bypassed and error injection has no
   effect.

 fs/xfs/libxfs/xfs_bmap.c | 115 ++++++++++++++++++++++++++++++++++++---
 fs/xfs/libxfs/xfs_bmap.h |   3 +
 fs/xfs/xfs_reflink.c     |  15 +----
 3 files changed, 110 insertions(+), 23 deletions(-)

diff --git a/fs/xfs/libxfs/xfs_bmap.c b/fs/xfs/libxfs/xfs_bmap.c
index 8eb1d1ed7b75..b7649ad5f18d 100644
--- a/fs/xfs/libxfs/xfs_bmap.c
+++ b/fs/xfs/libxfs/xfs_bmap.c
@@ -5880,6 +5880,112 @@ xfs_bmap_collapse_extents(
 	return error;
 }
 
+/* Deferred mapping is only for real extents in the data fork. */
+static bool
+xfs_bmap_is_update_needed(
+	struct xfs_bmbt_irec	*bmap)
+{
+	return  bmap->br_startblock != HOLESTARTBLOCK &&
+		bmap->br_startblock != DELAYSTARTBLOCK;
+}
+
+/* del is an extent from COW fork */
+int
+xfs_bremapi_from_cowfork(
+	struct xfs_trans	*tp,
+	struct xfs_inode	*ip,
+	struct xfs_bmbt_irec	*icow)
+{
+	int			error;
+	xfs_filblks_t		rlen;
+
+	if (xfs_bmap_is_update_needed(icow)) {
+		xfs_fileoff_t		start, end, max_len;
+		struct xfs_bmbt_irec	got;
+		struct xfs_iext_cursor	icur;
+		struct xfs_btree_cur	*cur = NULL;
+		struct xfs_ifork	*ifp = XFS_IFORK_PTR(ip, XFS_DATA_FORK);
+		int			logflags = 0;
+
+		error = xfs_iread_extents(tp, ip, XFS_DATA_FORK);
+		if (error)
+			return error;
+
+		max_len = xfs_refcount_max_unmap(tp->t_log_res);
+		if (max_len < icow->br_blockcount) {
+			icow->br_startoff += icow->br_blockcount - max_len;
+			icow->br_startblock += icow->br_blockcount - max_len;
+			icow->br_blockcount = max_len;
+		}
+
+		end = icow->br_startoff + icow->br_blockcount;
+		if (!xfs_iext_count(ifp) || !xfs_iext_lookup_extent_before(ip,
+				ifp, &end, &icur, &got) ||
+		    isnullstartblock(got.br_startblock) ||
+		    icow->br_startoff + icow->br_blockcount > got.br_startoff +
+				got.br_blockcount) {
+			error = -EAGAIN;
+		} else {
+			end = icow->br_startoff + icow->br_blockcount;
+			start = XFS_FILEOFF_MAX(icow->br_startoff,
+						got.br_startoff);
+			ASSERT(start < end);
+
+			/* Trim the extent to what we need */
+			xfs_trim_extent(icow, start, end - start);
+			xfs_trim_extent(&got, start, end - start);
+
+			if (ifp->if_format == XFS_DINODE_FMT_BTREE) {
+				cur = xfs_bmbt_init_cursor(tp->t_mountp, tp, ip,
+							   XFS_DATA_FORK);
+				cur->bc_ino.flags = 0;
+			}
+
+			/*
+			 * Free the CoW orphan record (it should be done here
+			 * before updating extent due to rmapbt update)
+			 */
+			xfs_refcount_free_cow_extent(tp, icow->br_startblock,
+						     icow->br_blockcount);
+
+			xfs_bmap_update_extent_real(tp, ip, XFS_DATA_FORK,
+					&icur, &cur, icow, &logflags, false);
+
+			/* Free previous referenced space */
+			xfs_refcount_decrease_extent(tp, &got);
+
+			/* Unchange the previous referenced quota */
+			xfs_trans_mod_dquot_byino(tp, ip, XFS_TRANS_DQ_BCOUNT,
+						  -(int)got.br_blockcount);
+			trace_xfs_reflink_cow_remap(ip, icow);
+			error = 0;
+		}
+		if (cur)
+			xfs_btree_del_cursor(cur, 0);
+		if (logflags)
+			xfs_trans_log_inode(tp, ip, logflags);
+		if (!error)
+			return 0;
+	}
+
+	rlen = icow->br_blockcount;
+	error = __xfs_bunmapi(tp, ip, icow->br_startoff, &rlen, 0, 1);
+	if (error)
+		return error;
+
+	/* Trim the extent to whatever got unmapped. */
+	xfs_trim_extent(icow, icow->br_startoff + rlen,
+			icow->br_blockcount - rlen);
+	/* Free the CoW orphan record. */
+	xfs_refcount_free_cow_extent(tp, icow->br_startblock,
+				     icow->br_blockcount);
+
+	/* Map the new blocks into the data fork. */
+	xfs_bmap_map_extent(tp, ip, icow);
+	trace_xfs_reflink_cow_remap(ip, icow);
+	return 0;
+}
+
 /* Make sure we won't be right-shifting an extent past the maximum bound. */
 int
 xfs_bmap_can_insert_extents(
@@ -6123,15 +6229,6 @@ xfs_bmap_split_extent(
 	return error;
 }
 
-/* Deferred mapping is only for real extents in the data fork. */
-static bool
-xfs_bmap_is_update_needed(
-	struct xfs_bmbt_irec	*bmap)
-{
-	return  bmap->br_startblock != HOLESTARTBLOCK &&
-		bmap->br_startblock != DELAYSTARTBLOCK;
-}
-
 /* Record a bmap intent. */
 static int
 __xfs_bmap_add(
diff --git a/fs/xfs/libxfs/xfs_bmap.h b/fs/xfs/libxfs/xfs_bmap.h
index c52ff94786e2..9da1cff41c1c 100644
--- a/fs/xfs/libxfs/xfs_bmap.h
+++ b/fs/xfs/libxfs/xfs_bmap.h
@@ -220,6 +220,9 @@ int	xfs_bmap_update_extent_real(struct xfs_trans *tp,
 		struct xfs_inode *ip, int whichfork,
 		struct xfs_iext_cursor *icur, struct xfs_btree_cur **curp,
 		struct xfs_bmbt_irec *new, int *logflagsp, bool convert);
+int
+xfs_bremapi_from_cowfork(struct xfs_trans *tp, struct xfs_inode *ip,
+		struct xfs_bmbt_irec *icow);
 
 enum xfs_bmap_intent_type {
 	XFS_BMAP_MAP = 1,
diff --git a/fs/xfs/xfs_reflink.c b/fs/xfs/xfs_reflink.c
index 276387a6a85d..0cddee8feda0 100644
--- a/fs/xfs/xfs_reflink.c
+++ b/fs/xfs/xfs_reflink.c
@@ -590,7 +590,6 @@ xfs_reflink_end_cow_extent(
 	struct xfs_mount	*mp = ip->i_mount;
 	struct xfs_trans	*tp;
 	struct xfs_ifork	*ifp = XFS_IFORK_PTR(ip, XFS_COW_FORK);
-	xfs_filblks_t		rlen;
 	unsigned int		resblks;
 	int			error;
 
@@ -651,22 +650,10 @@ xfs_reflink_end_cow_extent(
 		goto out_cancel;
 	}
 
-	/* Unmap the old blocks in the data fork. */
-	rlen = del.br_blockcount;
-	error = __xfs_bunmapi(tp, ip, del.br_startoff, &rlen, 0, 1);
+	error = xfs_bremapi_from_cowfork(tp, ip, &del);
 	if (error)
 		goto out_cancel;
 
-	/* Trim the extent to whatever got unmapped. */
-	xfs_trim_extent(&del, del.br_startoff + rlen, del.br_blockcount - rlen);
-	trace_xfs_reflink_cow_remap(ip, &del);
-
-	/* Free the CoW orphan record. */
-	xfs_refcount_free_cow_extent(tp, del.br_startblock, del.br_blockcount);
-
-	/* Map the new blocks into the data fork. */
-	xfs_bmap_map_extent(tp, ip, &del);
-
 	/* Charge this new data fork mapping to the on-disk quota. */
 	xfs_trans_mod_dquot_byino(tp, ip, XFS_TRANS_DQ_DELBCOUNT,
 			(long)del.br_blockcount);
-- 
2.24.4