rbd: encapsulate code that gets snapshot info

Create a function that encapsulates looking up the name, size and
features related to a given snapshot, which is indicated by its
index in an rbd device's snapshot context array of snapshot ids.

This interface will be used to hide differences between the format 1
and format 2 images.

At the moment this (looking up the name anyway) is slightly less
efficient than what's done currently, but we may be able to optimize
this a bit later on by cacheing the last lookup if it proves to be a
problem.

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

1 files changed, 30 insertions, 6 deletions

diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c
index 463f8b264c6f..366a3a1f2aac 100644
--- a/drivers/block/rbd.c
+++ b/drivers/block/rbd.c
@@ -2102,6 +2102,25 @@ err:
         return ERR_PTR(ret);
 }
 
+static char *rbd_dev_v1_snap_info(struct rbd_device *rbd_dev, u32 which,
+                u64 *snap_size, u64 *snap_features)
+{
+        char *snap_name;
+
+        rbd_assert(which < rbd_dev->header.snapc->num_snaps);
+
+        *snap_size = rbd_dev->header.snap_sizes[which];
+        *snap_features = 0;     /* No features for v1 */
+
+        /* Skip over names until we find the one we are looking for */
+
+        snap_name = rbd_dev->header.snap_names;
+        while (which--)
+                snap_name += strlen(snap_name) + 1;
+
+        return snap_name;
+}
+
 /*
  * Scan the rbd device's current snapshot list and compare it to the
  * newly-received snapshot context.  Remove any existing snapshots
@@ -2118,7 +2137,6 @@ 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;
-        char *snap_name = rbd_dev->header.snap_names;
         struct list_head *head = &rbd_dev->snaps;
         struct list_head *links = head->next;
         u32 index = 0;
@@ -2127,6 +2145,9 @@ static int rbd_dev_snaps_update(struct rbd_device *rbd_dev)
         while (index < snap_count || links != head) {
                 u64 snap_id;
                 struct rbd_snap *snap;
+                char *snap_name;
+                u64 snap_size = 0;
+                u64 snap_features = 0;
 
                 snap_id = index < snap_count ? snapc->snaps[index]
                                              : CEPH_NOSNAP;
@@ -2153,16 +2174,20 @@ static int rbd_dev_snaps_update(struct rbd_device *rbd_dev)
                         continue;
                 }
 
+                snap_name = rbd_dev_v1_snap_info(rbd_dev, index,
+                                                &snap_size, &snap_features);
+                if (IS_ERR(snap_name))
+                        return PTR_ERR(snap_name);
+
                 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_image_header *header = &rbd_dev->header;
                         struct rbd_snap *new_snap;
 
                         /* We haven't seen this snapshot before */
 
                         new_snap = __rbd_add_snap_dev(rbd_dev, snap_name,
-                                        snap_id, header->snap_sizes[index], 0);
+                                        snap_id, snap_size, snap_features);
                         if (IS_ERR(new_snap)) {
                                 int err = PTR_ERR(new_snap);
 
@@ -2183,9 +2208,9 @@ static int rbd_dev_snaps_update(struct rbd_device *rbd_dev)
 
                         dout("  already present\n");
 
-                        rbd_assert(snap->size ==
-                                        rbd_dev->header.snap_sizes[index]);
+                        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 */
 
@@ -2195,7 +2220,6 @@ static int rbd_dev_snaps_update(struct rbd_device *rbd_dev)
                 /* Advance to the next entry in the snapshot context */
 
                 index++;
-                snap_name += strlen(snap_name) + 1;
         }
         dout("%s: done\n", __func__);