rbd: split rbd_dev_spec_update() into two functions

rbd_dev_spec_update() has two modes of operation, with nothing in
common between them.  Split it into two functions, one for each mode
and make our expectations more clear.
Signed-off-by: Ilya Dryomov <ilya.dryomov@inktank.com>
Reviewed-by: Alex Elder <elder@linaro.org>

drivers/block/rbd.c

@@ -3798,6 +3798,9 @@ static struct rbd_spec *rbd_spec_alloc(void)
 	spec = kzalloc(sizeof (*spec), GFP_KERNEL);
 	if (!spec)
 		return NULL;
+
+	spec->pool_id = CEPH_NOPOOL;
+	spec->snap_id = CEPH_NOSNAP;
 	kref_init(&spec->kref);
 
 	return spec;
@@ -4257,44 +4260,49 @@ static u64 rbd_snap_id_by_name(struct rbd_device *rbd_dev, const char *name)
 }
 
 /*
- * When an rbd image has a parent image, it is identified by the
- * pool, image, and snapshot ids (not names).  This function fills
- * in the names for those ids.  (It's OK if we can't figure out the
- * name for an image id, but the pool and snapshot ids should always
- * exist and have names.)  All names in an rbd spec are dynamically
- * allocated.
- *
- * When an image being mapped (not a parent) is probed, we have the
- * pool name and pool id, image name and image id, and the snapshot
- * name.  The only thing we're missing is the snapshot id.
+ * An image being mapped will have everything but the snap id.
  */
-static int rbd_dev_spec_update(struct rbd_device *rbd_dev)
+static int rbd_spec_fill_snap_id(struct rbd_device *rbd_dev)
 {
-	struct ceph_osd_client *osdc = &rbd_dev->rbd_client->client->osdc;
 	struct rbd_spec *spec = rbd_dev->spec;
-	const char *pool_name;
-	const char *image_name;
-	const char *snap_name;
-	int ret;
 
-	/*
-	 * An image being mapped will have the pool name (etc.), but
-	 * we need to look up the snapshot id.
-	 */
-	if (spec->pool_name) {
+	rbd_assert(spec->pool_id != CEPH_NOPOOL && spec->pool_name);
+	rbd_assert(spec->image_id && spec->image_name);
+	rbd_assert(spec->snap_name);
+
 	if (strcmp(spec->snap_name, RBD_SNAP_HEAD_NAME)) {
 		u64 snap_id;
 
 		snap_id = rbd_snap_id_by_name(rbd_dev, spec->snap_name);
 		if (snap_id == CEPH_NOSNAP)
 			return -ENOENT;
+
 		spec->snap_id = snap_id;
 	} else {
 		spec->snap_id = CEPH_NOSNAP;
 	}
 
 	return 0;
-	}
+}
+
+/*
+ * A parent image will have all ids but none of the names.
+ *
+ * All names in an rbd spec are dynamically allocated.  It's OK if we
+ * can't figure out the name for an image id.
+ */
+static int rbd_spec_fill_names(struct rbd_device *rbd_dev)
+{
+	struct ceph_osd_client *osdc = &rbd_dev->rbd_client->client->osdc;
+	struct rbd_spec *spec = rbd_dev->spec;
+	const char *pool_name;
+	const char *image_name;
+	const char *snap_name;
+	int ret;
+
+	rbd_assert(spec->pool_id != CEPH_NOPOOL);
+	rbd_assert(spec->image_id);
+	rbd_assert(spec->snap_id != CEPH_NOSNAP);
 
 	/* Get the pool name; we have to make our own copy of this */
 
@@ -4313,7 +4321,7 @@ static int rbd_dev_spec_update(struct rbd_device *rbd_dev)
 	if (!image_name)
 		rbd_warn(rbd_dev, "unable to get image name");
 
-	/* Look up the snapshot name, and make a copy */
+	/* Fetch the snapshot name */
 
 	snap_name = rbd_snap_name(rbd_dev, spec->snap_id);
 	if (IS_ERR(snap_name)) {
@@ -4326,10 +4334,10 @@ static int rbd_dev_spec_update(struct rbd_device *rbd_dev)
 	spec->snap_name = snap_name;
 
 	return 0;
+
 out_err:
 	kfree(image_name);
 	kfree(pool_name);
-
 	return ret;
 }
 
@@ -5158,7 +5166,16 @@ static int rbd_dev_image_probe(struct rbd_device *rbd_dev, bool mapping)
 	if (ret)
 		goto err_out_watch;
 
-	ret = rbd_dev_spec_update(rbd_dev);
+	/*
+	 * If this image is the one being mapped, we have pool name and
+	 * id, image name and id, and snap name - need to fill snap id.
+	 * Otherwise this is a parent image, identified by pool, image
+	 * and snap ids - need to fill in names for those ids.
+	 */
+	if (mapping)
+		ret = rbd_spec_fill_snap_id(rbd_dev);
+	else
+		ret = rbd_spec_fill_names(rbd_dev);
 	if (ret)
 		goto err_out_probe;