rbd: rename __rbd_init_snaps_header()

The name __rbd_init_snaps_header() doesn't really convey what that
function does very well.  Its purpose is to scan a new snapshot
context and either create or destroy snapshot device entries so
that local host's view is consistent with the reality maintained
on the OSDs.  This patch just changes the name of this function,
to be rbd_dev_snap_devs_update().  Still not perfect, but I think
better.

Also add some dynamic debug statements to this function.

Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>

drivers/block/rbd.c

@@ -201,7 +201,7 @@ static DEFINE_SPINLOCK(rbd_dev_list_lock);
 static LIST_HEAD(rbd_client_list);		/* clients */
 static DEFINE_SPINLOCK(rbd_client_list_lock);
 
-static int __rbd_init_snaps_header(struct rbd_device *rbd_dev);
+static int rbd_dev_snap_devs_update(struct rbd_device *rbd_dev);
 static void rbd_dev_release(struct device *dev);
 static ssize_t rbd_snap_add(struct device *dev,
 			    struct device_attribute *attr,
@@ -1848,7 +1848,7 @@ static int __rbd_refresh_header(struct rbd_device *rbd_dev, u64 *hver)
 	WARN_ON(strcmp(rbd_dev->header.object_prefix, h.object_prefix));
 	kfree(h.object_prefix);
 
-	ret = __rbd_init_snaps_header(rbd_dev);
+	ret = rbd_dev_snap_devs_update(rbd_dev);
 
 	up_write(&rbd_dev->header_rwsem);
 
@@ -1880,7 +1880,7 @@ static int rbd_init_disk(struct rbd_device *rbd_dev)
 		return rc;
 
 	/* no need to lock here, as rbd_dev is not registered yet */
-	rc = __rbd_init_snaps_header(rbd_dev);
+	rc = rbd_dev_snap_devs_update(rbd_dev);
 	if (rc)
 		return rc;
 
@@ -2184,7 +2184,7 @@ static struct rbd_snap *__rbd_add_snap_dev(struct rbd_device *rbd_dev,
  * snapshot id, highest id first.  (Snapshots in the rbd_dev's list
  * are also maintained in that order.)
  */
-static int __rbd_init_snaps_header(struct rbd_device *rbd_dev)
+static int rbd_dev_snap_devs_update(struct rbd_device *rbd_dev)
 {
 	struct ceph_snap_context *snapc = rbd_dev->header.snapc;
 	const u32 snap_count = snapc->num_snaps;
@@ -2193,6 +2193,7 @@ static int __rbd_init_snaps_header(struct rbd_device *rbd_dev)
 	struct list_head *links = head->next;
 	u32 index = 0;
 
+	dout("%s: snap count is %u\n", __func__, (unsigned int) snap_count);
 	while (index < snap_count || links != head) {
 		u64 snap_id;
 		struct rbd_snap *snap;
@@ -2211,32 +2212,45 @@ static int __rbd_init_snaps_header(struct rbd_device *rbd_dev)
 			if (rbd_dev->snap_id == snap->id)
 				rbd_dev->snap_exists = false;
 			__rbd_remove_snap_dev(snap);
+			dout("%ssnap id %llu has been removed\n",
+				rbd_dev->snap_id == snap->id ? "mapped " : "",
+				(unsigned long long) snap->id);
 
 			/* Done with this list entry; advance */
 
 			links = next;
 			continue;
 		}
 
+		dout("entry %u: snap_id = %llu\n", (unsigned int) snap_count,
+			(unsigned long long) snap_id);
 		if (!snap || (snap_id != CEPH_NOSNAP && snap->id < snap_id)) {
 			struct rbd_snap *new_snap;
 
 			/* We haven't seen this snapshot before */
 
 			new_snap = __rbd_add_snap_dev(rbd_dev, index,
 							snap_name);
-			if (IS_ERR(new_snap))
-				return PTR_ERR(new_snap);
+			if (IS_ERR(new_snap)) {
+				int err = PTR_ERR(new_snap);
+
+				dout("  failed to add dev, error %d\n", err);
+
+				return err;
+			}
 
 			/* New goes before existing, or at end of list */
 
+			dout("  added dev%s\n", snap ? "" : " at end\n");
 			if (snap)
 				list_add_tail(&new_snap->node, &snap->node);
 			else
 				list_add_tail(&new_snap->node, head);
 		} else {
 			/* Already have this one */
 
+			dout("  already present\n");
+
 			rbd_assert(snap->size ==
 					rbd_dev->header.snap_sizes[index]);
 			rbd_assert(!strcmp(snap->name, snap_name));
@@ -2251,6 +2265,7 @@ static int __rbd_init_snaps_header(struct rbd_device *rbd_dev)
 		index++;
 		snap_name += strlen(snap_name) + 1;
 	}
+	dout("%s: done\n", __func__);
 
 	return 0;
 }