rbd: record mapped size

Add the size of the mapped image to the set of mapping-specific
fields in an rbd_device, and use it when setting the capacity of the
disk.
Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>

drivers/block/rbd.c

@@ -151,6 +151,7 @@ struct rbd_snap {
 struct rbd_mapping {
 	char                    *snap_name;
 	u64                     snap_id;
+	u64                     size;
 	bool                    snap_exists;
 	bool			read_only;
 };
@@ -643,7 +644,7 @@ static int snap_by_name(struct rbd_image_header *header, const char *snap_name,
 	return -ENOENT;
 }
 
-static int rbd_header_set_snap(struct rbd_device *rbd_dev, u64 *size)
+static int rbd_header_set_snap(struct rbd_device *rbd_dev)
 {
 	int ret;
 
@@ -652,19 +653,16 @@ static int rbd_header_set_snap(struct rbd_device *rbd_dev, u64 *size)
 	if (!memcmp(rbd_dev->mapping.snap_name, RBD_SNAP_HEAD_NAME,
 		    sizeof (RBD_SNAP_HEAD_NAME))) {
 		rbd_dev->mapping.snap_id = CEPH_NOSNAP;
+		rbd_dev->mapping.size = rbd_dev->header.image_size;
 		rbd_dev->mapping.snap_exists = false;
 		rbd_dev->mapping.read_only = rbd_dev->rbd_opts.read_only;
-		if (size)
-			*size = rbd_dev->header.image_size;
 	} else {
-		u64 snap_id = 0;
-
 		ret = snap_by_name(&rbd_dev->header,
 					rbd_dev->mapping.snap_name,
-					&snap_id, size);
+					&rbd_dev->mapping.snap_id,
+					&rbd_dev->mapping.size);
 		if (ret < 0)
 			goto done;
-		rbd_dev->mapping.snap_id = snap_id;
 		rbd_dev->mapping.snap_exists = true;
 		rbd_dev->mapping.read_only = true;
 	}
@@ -1830,8 +1828,12 @@ static int __rbd_refresh_header(struct rbd_device *rbd_dev, u64 *hver)
 	if (rbd_dev->mapping.snap_id == CEPH_NOSNAP) {
 		sector_t size = (sector_t) h.image_size / SECTOR_SIZE;
 
-		dout("setting size to %llu sectors", (unsigned long long) size);
-		set_capacity(rbd_dev->disk, size);
+		if (size != (sector_t) rbd_dev->mapping.size) {
+			dout("setting size to %llu sectors",
+				(unsigned long long) size);
+			rbd_dev->mapping.size = (u64) size;
+			set_capacity(rbd_dev->disk, size);
+		}
 	}
 
 	/* rbd_dev->header.object_prefix shouldn't change */
@@ -1875,7 +1877,6 @@ static int rbd_init_disk(struct rbd_device *rbd_dev)
 	struct request_queue *q;
 	int rc;
 	u64 segment_size;
-	u64 total_size = 0;
 
 	/* contact OSD, request size info about the object being mapped */
 	rc = rbd_read_header(rbd_dev, &rbd_dev->header);
@@ -1887,7 +1888,7 @@ static int rbd_init_disk(struct rbd_device *rbd_dev)
 	if (rc)
 		return rc;
 
-	rc = rbd_header_set_snap(rbd_dev, &total_size);
+	rc = rbd_header_set_snap(rbd_dev);
 	if (rc)
 		return rc;
 
@@ -1928,11 +1929,11 @@ static int rbd_init_disk(struct rbd_device *rbd_dev)
 	rbd_dev->disk = disk;
 
 	/* finally, announce the disk to the world */
-	set_capacity(disk, total_size / SECTOR_SIZE);
+	set_capacity(disk, (sector_t) rbd_dev->mapping.size / SECTOR_SIZE);
 	add_disk(disk);
 
 	pr_info("%s: added with size 0x%llx\n",
-		disk->disk_name, (unsigned long long)total_size);
+		disk->disk_name, (unsigned long long) rbd_dev->mapping.size);
 	return 0;
 
 out_disk: