1 files changed, 89 insertions, 0 deletions
diff --git a/fs/xfs/xfs_bmap_util.c b/fs/xfs/xfs_bmap_util.c
index 3b9f262f8e91..c88b9ade7389 100644
--- a/fs/xfs/xfs_bmap_util.c
+++ b/fs/xfs/xfs_bmap_util.c
@@ -1744,3 +1744,92 @@ out_trans_cancel:
 	xfs_trans_cancel(tp);
 	goto out_unlock_ilock;
 }
+
+/*
+ * Given a CoW fork mapping @got and a replacement mapping @rep, map the space
+ * described by @rep into the cow fork, pushing aside @got as necessary.  @icur
+ * must point to iext tree leaf containing @got.
+ */
+void
+xfs_bmap_replace_cow_mapping(
+	struct xfs_inode	*ip,
+	struct xfs_iext_cursor	*icur,
+	struct xfs_bmbt_irec	*got,
+	struct xfs_bmbt_irec	*rep)
+{
+	struct xfs_ifork	*ifp = xfs_ifork_ptr(ip, XFS_COW_FORK);
+	xfs_fileoff_t		rep_endoff =
+			rep->br_startoff + rep->br_blockcount;
+	xfs_fileoff_t		got_endoff =
+			got->br_startoff + got->br_blockcount;
+	uint32_t		state = BMAP_COWFORK;
+
+	ASSERT(rep->br_blockcount > 0);
+	ASSERT(!isnullstartblock(got->br_startblock));
+	ASSERT(got->br_startoff <= rep->br_startoff);
+	ASSERT(got_endoff >= rep_endoff);
+
+	trace_xfs_bmap_replace_cow_mapping(ip, got, rep);
+
+	if (got->br_startoff == rep->br_startoff)
+		state |= BMAP_LEFT_FILLING;
+	if (got_endoff == rep_endoff)
+		state |= BMAP_RIGHT_FILLING;
+
+	switch (state & (BMAP_LEFT_FILLING | BMAP_RIGHT_FILLING)) {
+	case BMAP_LEFT_FILLING | BMAP_RIGHT_FILLING:
+		/*
+		 * Replacement matches the whole mapping, update the record.
+		 */
+		xfs_iext_update_extent(ip, state, icur, rep);
+		break;
+	case BMAP_LEFT_FILLING:
+		/*
+		 * Replace the first part of the mapping: Update the cursor
+		 * position with the new mapping, then add a record with the
+		 * tail of the old mapping.
+		 */
+		got->br_startoff = rep_endoff;
+		got->br_blockcount -= rep->br_blockcount;
+		got->br_startblock += rep->br_blockcount;
+
+		xfs_iext_update_extent(ip, state, icur, rep);
+		xfs_iext_next(ifp, icur);
+		xfs_iext_insert(ip, icur, got, state);
+		break;
+	case BMAP_RIGHT_FILLING:
+		/*
+		 * Replacing the last part of the mapping.  Shorten the current
+		 * mapping then add a record with the new mapping.
+		 */
+		got->br_blockcount -= rep->br_blockcount;
+
+		xfs_iext_update_extent(ip, state, icur, got);
+		xfs_iext_next(ifp, icur);
+		xfs_iext_insert(ip, icur, rep, state);
+		break;
+	case 0:
+		/*
+		 * Replacing the middle of the extent.  Shorten the current
+		 * mapping, add a new record with the new mapping, and add a
+		 * second new record with the tail of the old mapping.
+		 */
+		got->br_blockcount = rep->br_startoff - got->br_startoff;
+
+		struct xfs_bmbt_irec	new = {
+			.br_startoff	= rep_endoff,
+			.br_blockcount	= got_endoff - rep_endoff,
+			.br_state	= got->br_state,
+			.br_startblock	= got->br_startblock +
+						rep->br_blockcount +
+						got->br_blockcount,
+		};
+
+		xfs_iext_update_extent(ip, state, icur, got);
+		xfs_iext_next(ifp, icur);
+		xfs_iext_insert(ip, icur, rep, state);
+		xfs_iext_next(ifp, icur);
+		xfs_iext_insert(ip, icur, &new, state);
+		break;
+	}
+}