pnfsblock: merge rw extents

Signed-off-by: NFred Isaman <iisaman@citi.umich.edu>
Signed-off-by: NBenny Halevy <bhalevy@panasas.com>
Signed-off-by: NBenny Halevy <bhalevy@tonian.com>
Signed-off-by: NJim Rees <rees@umich.edu>
Signed-off-by: NTrond Myklebust <Trond.Myklebust@netapp.com>

fs/nfs/blocklayout/extents.c

@@ -493,3 +493,50 @@ bl_find_get_extent(struct pnfs_block_layout *bl, sector_t isect,
 	print_bl_extent(ret);
 	return ret;
 }
+
+/* Helper function to set_to_rw that initialize a new extent */
+static void
+_prep_new_extent(struct pnfs_block_extent *new,
+		 struct pnfs_block_extent *orig,
+		 sector_t offset, sector_t length, int state)
+{
+	kref_init(&new->be_refcnt);
+	/* don't need to INIT_LIST_HEAD(&new->be_node) */
+	memcpy(&new->be_devid, &orig->be_devid, sizeof(struct nfs4_deviceid));
+	new->be_mdev = orig->be_mdev;
+	new->be_f_offset = offset;
+	new->be_length = length;
+	new->be_v_offset = orig->be_v_offset - orig->be_f_offset + offset;
+	new->be_state = state;
+	new->be_inval = orig->be_inval;
+}
+
+/* Tries to merge be with extent in front of it in list.
+ * Frees storage if not used.
+ */
+static struct pnfs_block_extent *
+_front_merge(struct pnfs_block_extent *be, struct list_head *head,
+	     struct pnfs_block_extent *storage)
+{
+	struct pnfs_block_extent *prev;
+
+	if (!storage)
+		goto no_merge;
+	if (&be->be_node == head || be->be_node.prev == head)
+		goto no_merge;
+	prev = list_entry(be->be_node.prev, struct pnfs_block_extent, be_node);
+	if ((prev->be_f_offset + prev->be_length != be->be_f_offset) ||
+	    !extents_consistent(prev, be))
+		goto no_merge;
+	_prep_new_extent(storage, prev, prev->be_f_offset,
+			 prev->be_length + be->be_length, prev->be_state);
+	list_replace(&prev->be_node, &storage->be_node);
+	bl_put_extent(prev);
+	list_del(&be->be_node);
+	bl_put_extent(be);
+	return storage;
+
+ no_merge:
+	kfree(storage);
+	return be;
+}