rbd: kill off the snapshot list

We no longer use the snapshot list for anything.  When we need to
look up a snapshot name, id, size, or feature mask, we just do it
directly rather than relying on this list being updated with every
refresh.  The main reason it existed was for the benefit of the
device/sysfs entries that previously were associated with snapshots.

So get rid of the snapshot list, and struct rbd_snap, and the
hundreds of lines of code that supported them.

This resolves:
    http://tracker.ceph.com/issues/4868

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

drivers/block/rbd.c

@@ -274,14 +274,6 @@ struct rbd_img_request {
 #define for_each_obj_request_safe(ireq, oreq, n) \
 	list_for_each_entry_safe_reverse(oreq, n, &(ireq)->obj_requests, links)
 
-struct rbd_snap {
-	const char		*name;
-	u64			size;
-	struct list_head	node;
-	u64			id;
-	u64			features;
-};
-
 struct rbd_mapping {
 	u64                     size;
 	u64                     features;
@@ -326,9 +318,6 @@ struct rbd_device {
 
 	struct list_head	node;
 
-	/* list of snapshots */
-	struct list_head	snaps;
-
 	/* sysfs related */
 	struct device		dev;
 	unsigned long		open_count;	/* protected by lock */
@@ -356,10 +345,7 @@ static DEFINE_SPINLOCK(rbd_client_list_lock);
 
 static int rbd_img_request_submit(struct rbd_img_request *img_request);
 
-static int rbd_dev_snaps_update(struct rbd_device *rbd_dev);
-
 static void rbd_dev_device_release(struct device *dev);
-static void rbd_snap_destroy(struct rbd_snap *snap);
 
 static ssize_t rbd_add(struct bus_type *bus, const char *buf,
 		       size_t count);
@@ -3075,17 +3061,6 @@ static int rbd_read_header(struct rbd_device *rbd_dev,
 	return ret;
 }
 
-static void rbd_remove_all_snaps(struct rbd_device *rbd_dev)
-{
-	struct rbd_snap *snap;
-	struct rbd_snap *next;
-
-	list_for_each_entry_safe(snap, next, &rbd_dev->snaps, node) {
-		list_del(&snap->node);
-		rbd_snap_destroy(snap);
-	}
-}
-
 static void rbd_update_mapping_size(struct rbd_device *rbd_dev)
 {
 	if (rbd_dev->spec->snap_id != CEPH_NOSNAP)
@@ -3134,8 +3109,6 @@ static int rbd_dev_v1_refresh(struct rbd_device *rbd_dev)
 		rbd_warn(rbd_dev, "object prefix changed (ignoring)");
 	kfree(h.object_prefix);
 
-	ret = rbd_dev_snaps_update(rbd_dev);
-
 	up_write(&rbd_dev->header_rwsem);
 
 	return ret;
@@ -3461,7 +3434,6 @@ static struct rbd_device *rbd_dev_create(struct rbd_client *rbdc,
 	spin_lock_init(&rbd_dev->lock);
 	rbd_dev->flags = 0;
 	INIT_LIST_HEAD(&rbd_dev->node);
-	INIT_LIST_HEAD(&rbd_dev->snaps);
 	init_rwsem(&rbd_dev->header_rwsem);
 
 	rbd_dev->spec = spec;
@@ -3484,54 +3456,6 @@ static void rbd_dev_destroy(struct rbd_device *rbd_dev)
 	kfree(rbd_dev);
 }
 
-static void rbd_snap_destroy(struct rbd_snap *snap)
-{
-	kfree(snap->name);
-	kfree(snap);
-}
-
-static struct rbd_snap *rbd_snap_create(struct rbd_device *rbd_dev,
-						const char *snap_name,
-						u64 snap_id, u64 snap_size,
-						u64 snap_features)
-{
-	struct rbd_snap *snap;
-
-	snap = kzalloc(sizeof (*snap), GFP_KERNEL);
-	if (!snap)
-		return ERR_PTR(-ENOMEM);
-
-	snap->name = snap_name;
-	snap->id = snap_id;
-	snap->size = snap_size;
-	snap->features = snap_features;
-
-	return snap;
-}
-
-/*
- * Returns a dynamically-allocated snapshot name if successful, or a
- * pointer-coded error otherwise.
- */
-static const char *rbd_dev_v1_snap_info(struct rbd_device *rbd_dev,
-			u64 snap_id, u64 *snap_size, u64 *snap_features)
-{
-	const char *snap_name;
-	u32 which;
-
-	which = rbd_dev_snap_index(rbd_dev, snap_id);
-	if (which == BAD_SNAP_INDEX)
-		return ERR_PTR(-ENOENT);
-	snap_name = _rbd_dev_v1_snap_name(rbd_dev, which);
-	if (!snap_name)
-		return ERR_PTR(-ENOMEM);
-
-	*snap_size = rbd_dev->header.snap_sizes[which];
-	*snap_features = 0;	/* No features for v1 */
-
-	return snap_name;
-}
-
 /*
  * Get the size and object order for an image snapshot, or if
  * snap_id is CEPH_NOSNAP, gets this information for the base
@@ -3883,10 +3807,6 @@ static u64 rbd_snap_id_by_name(struct rbd_device *rbd_dev, const char *name)
  * 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_spec_update(struct rbd_device *rbd_dev)
 {
@@ -4065,45 +3985,6 @@ out:
 	return snap_name;
 }
 
-static const char *rbd_dev_v2_snap_info(struct rbd_device *rbd_dev,
-			u64 snap_id, u64 *snap_size, u64 *snap_features)
-{
-	u64 size;
-	u64 features;
-	const char *snap_name;
-	int ret;
-
-	ret = _rbd_dev_v2_snap_size(rbd_dev, snap_id, NULL, &size);
-	if (ret)
-		goto out_err;
-
-	ret = _rbd_dev_v2_snap_features(rbd_dev, snap_id, &features);
-	if (ret)
-		goto out_err;
-
-	snap_name = rbd_dev_v2_snap_name(rbd_dev, snap_id);
-	if (!IS_ERR(snap_name)) {
-		*snap_size = size;
-		*snap_features = features;
-	}
-
-	return snap_name;
-out_err:
-	return ERR_PTR(ret);
-}
-
-static const char *rbd_dev_snap_info(struct rbd_device *rbd_dev,
-		u64 snap_id, u64 *snap_size, u64 *snap_features)
-{
-	if (rbd_dev->image_format == 1)
-		return rbd_dev_v1_snap_info(rbd_dev, snap_id,
-					snap_size, snap_features);
-	if (rbd_dev->image_format == 2)
-		return rbd_dev_v2_snap_info(rbd_dev, snap_id,
-					snap_size, snap_features);
-	return ERR_PTR(-EINVAL);
-}
-
 static int rbd_dev_v2_refresh(struct rbd_device *rbd_dev)
 {
 	int ret;
@@ -4119,141 +4000,12 @@ static int rbd_dev_v2_refresh(struct rbd_device *rbd_dev)
 	dout("rbd_dev_v2_snap_context returned %d\n", ret);
 	if (ret)
 		goto out;
-	ret = rbd_dev_snaps_update(rbd_dev);
-	dout("rbd_dev_snaps_update returned %d\n", ret);
-	if (ret)
-		goto out;
 out:
 	up_write(&rbd_dev->header_rwsem);
 
 	return ret;
 }
 
-/*
- * Scan the rbd device's current snapshot list and compare it to the
- * newly-received snapshot context.  Remove any existing snapshots
- * not present in the new snapshot context.  Add a new snapshot for
- * any snaphots in the snapshot context not in the current list.
- * And verify there are no changes to snapshots we already know
- * about.
- *
- * Assumes the snapshots in the snapshot context are sorted by
- * snapshot id, highest id first.  (Snapshots in the rbd_dev's list
- * are also maintained in that order.)
- *
- * Note that any error occurs while updating the snapshot list
- * aborts the update, and the entire list is cleared.  The snapshot
- * list becomes inconsistent at that point anyway, so it might as
- * well be empty.
- */
-static int rbd_dev_snaps_update(struct rbd_device *rbd_dev)
-{
-	struct ceph_snap_context *snapc = rbd_dev->header.snapc;
-	const u32 snap_count = snapc->num_snaps;
-	struct list_head *head = &rbd_dev->snaps;
-	struct list_head *links = head->next;
-	u32 index = 0;
-	int ret = 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;
-		const char *snap_name;
-		u64 snap_size = 0;
-		u64 snap_features = 0;
-
-		snap_id = index < snap_count ? snapc->snaps[index]
-					     : CEPH_NOSNAP;
-		snap = links != head ? list_entry(links, struct rbd_snap, node)
-				     : NULL;
-		rbd_assert(!snap || snap->id != CEPH_NOSNAP);
-
-		if (snap_id == CEPH_NOSNAP || (snap && snap->id > snap_id)) {
-			struct list_head *next = links->next;
-
-			/*
-			 * A previously-existing snapshot is not in
-			 * the new snap context.
-			 *
-			 * If the now-missing snapshot is the one
-			 * the image represents, clear its existence
-			 * flag so we can avoid sending any more
-			 * requests to it.
-			 */
-			if (rbd_dev->spec->snap_id == snap->id)
-				clear_bit(RBD_DEV_FLAG_EXISTS, &rbd_dev->flags);
-			dout("removing %ssnap id %llu\n",
-				rbd_dev->spec->snap_id == snap->id ?
-							"mapped " : "",
-				(unsigned long long)snap->id);
-
-			list_del(&snap->node);
-			rbd_snap_destroy(snap);
-
-			/* Done with this list entry; advance */
-
-			links = next;
-			continue;
-		}
-
-		snap_name = rbd_dev_snap_info(rbd_dev, snap_id,
-					&snap_size, &snap_features);
-		if (IS_ERR(snap_name)) {
-			ret = PTR_ERR(snap_name);
-			dout("failed to get snap info, error %d\n", ret);
-			goto out_err;
-		}
-
-		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_snap_create(rbd_dev, snap_name,
-					snap_id, snap_size, snap_features);
-			if (IS_ERR(new_snap)) {
-				ret = PTR_ERR(new_snap);
-				dout("  failed to add dev, error %d\n", ret);
-				goto out_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 == snap_size);
-			rbd_assert(!strcmp(snap->name, snap_name));
-			rbd_assert(snap->features == snap_features);
-
-			/* Done with this list entry; advance */
-
-			links = links->next;
-		}
-
-		/* Advance to the next entry in the snapshot context */
-
-		index++;
-	}
-	dout("%s: done\n", __func__);
-
-	return 0;
-out_err:
-	rbd_remove_all_snaps(rbd_dev);
-
-	return ret;
-}
-
 static int rbd_bus_add_dev(struct rbd_device *rbd_dev)
 {
 	struct device *dev;
@@ -4913,7 +4665,6 @@ static void rbd_dev_image_release(struct rbd_device *rbd_dev)
 {
 	int ret;
 
-	rbd_remove_all_snaps(rbd_dev);
 	rbd_dev_unprobe(rbd_dev);
 	ret = rbd_dev_header_watch_sync(rbd_dev, 0);
 	if (ret)
@@ -4963,20 +4714,14 @@ static int rbd_dev_image_probe(struct rbd_device *rbd_dev)
 	if (ret)
 		goto err_out_watch;
 
-	ret = rbd_dev_snaps_update(rbd_dev);
-	if (ret)
-		goto err_out_probe;
-
 	ret = rbd_dev_spec_update(rbd_dev);
 	if (ret)
-		goto err_out_snaps;
+		goto err_out_probe;
 
 	ret = rbd_dev_probe_parent(rbd_dev);
 	if (!ret)
 		return 0;
 
-err_out_snaps:
-	rbd_remove_all_snaps(rbd_dev);
 err_out_probe:
 	rbd_dev_unprobe(rbd_dev);
 err_out_watch: