rbd: refactor rbd_dev_probe_update_spec()

Fairly straightforward refactoring of rbd_dev_probe_update_spec().
The name is changed to rbd_dev_spec_update().

Rearrange it so nothing gets assigned to the spec until all of the
names have been successfully acquired.
Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>

drivers/block/rbd.c

@@ -3774,83 +3774,88 @@ static char *rbd_dev_image_name(struct rbd_device *rbd_dev)
 }
 
 /*
- * When a parent image gets probed, we only have the pool, image,
- * and snapshot ids but not the names of any of them.  This call
- * is made later to fill in those names.  It has to be done after
- * rbd_dev_snaps_update() has completed because some of the
- * information (in particular, snapshot name) is not available
- * until then.
+ * 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.
+ *
+ * The set of snapshots for an image is not known until they have
+ * been read by rbd_dev_snaps_update(), so we can't completely fill
+ * in this information until after that has been called.
  */
-static int rbd_dev_probe_update_spec(struct rbd_device *rbd_dev)
+static int rbd_dev_spec_update(struct rbd_device *rbd_dev)
 {
-	struct ceph_osd_client *osdc;
-	const char *name;
-	void *reply_buf = NULL;
+	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 (rbd_dev->spec->pool_name) {
-		if (strcmp(rbd_dev->spec->snap_name, RBD_SNAP_HEAD_NAME)) {
+	if (spec->pool_name) {
+		if (strcmp(spec->snap_name, RBD_SNAP_HEAD_NAME)) {
 			struct rbd_snap *snap;
 
-			snap = snap_by_name(rbd_dev, rbd_dev->spec->snap_name);
+			snap = snap_by_name(rbd_dev, spec->snap_name);
 			if (!snap)
 				return -ENOENT;
-			rbd_dev->spec->snap_id = snap->id;
+			spec->snap_id = snap->id;
 		} else {
-			rbd_dev->spec->snap_id = CEPH_NOSNAP;
+			spec->snap_id = CEPH_NOSNAP;
 		}
 
 		return 0;
 	}
 
-	/* Look up the pool name */
+	/* Get the pool name; we have to make our own copy of this */
 
-	osdc = &rbd_dev->rbd_client->client->osdc;
-	name = ceph_pg_pool_name_by_id(osdc->osdmap, rbd_dev->spec->pool_id);
-	if (!name) {
-		rbd_warn(rbd_dev, "there is no pool with id %llu",
-			rbd_dev->spec->pool_id);	/* Really a BUG() */
+	pool_name = ceph_pg_pool_name_by_id(osdc->osdmap, spec->pool_id);
+	if (!pool_name) {
+		rbd_warn(rbd_dev, "no pool with id %llu", spec->pool_id);
 		return -EIO;
 	}
-
-	rbd_dev->spec->pool_name = kstrdup(name, GFP_KERNEL);
-	if (!rbd_dev->spec->pool_name)
+	pool_name = kstrdup(pool_name, GFP_KERNEL);
+	if (!pool_name)
 		return -ENOMEM;
 
 	/* Fetch the image name; tolerate failure here */
 
-	name = rbd_dev_image_name(rbd_dev);
-	if (name)
-		rbd_dev->spec->image_name = (char *)name;
-	else
+	image_name = rbd_dev_image_name(rbd_dev);
+	if (!image_name)
 		rbd_warn(rbd_dev, "unable to get image name");
 
-	/* Look up the snapshot name. */
+	/* Look up the snapshot name, and make a copy */
 
-	name = rbd_snap_name(rbd_dev, rbd_dev->spec->snap_id);
-	if (!name) {
-		rbd_warn(rbd_dev, "no snapshot with id %llu",
-			rbd_dev->spec->snap_id);	/* Really a BUG() */
+	snap_name = rbd_snap_name(rbd_dev, spec->snap_id);
+	if (!snap_name) {
+		rbd_warn(rbd_dev, "no snapshot with id %llu", spec->snap_id);
 		ret = -EIO;
 		goto out_err;
 	}
-	rbd_dev->spec->snap_name = kstrdup(name, GFP_KERNEL);
-	if(!rbd_dev->spec->snap_name)
+	snap_name = kstrdup(snap_name, GFP_KERNEL);
+	if (!snap_name) {
+		ret = -ENOMEM;
 		goto out_err;
+	}
+
+	spec->pool_name = pool_name;
+	spec->image_name = image_name;
+	spec->snap_name = snap_name;
 
 	return 0;
 out_err:
-	kfree(reply_buf);
-	kfree(rbd_dev->spec->pool_name);
-	rbd_dev->spec->pool_name = NULL;
+	kfree(image_name);
+	kfree(pool_name);
 
 	return ret;
 }
@@ -4710,7 +4715,7 @@ static int rbd_dev_probe_finish(struct rbd_device *rbd_dev)
 	if (ret)
 		return ret;
 
-	ret = rbd_dev_probe_update_spec(rbd_dev);
+	ret = rbd_dev_spec_update(rbd_dev);
 	if (ret)
 		goto err_out_snaps;