librbd: make group and group snapshot IDs more random

Image IDs suffered from the same issue -- it was addressed in commit
be83736 ("librbd: block_name_prefix is not created randomly").
The code for generating group IDs is duplicated in api/Group.cc and
got missed.

Instead of cut-and-pasting the fix, just call generate_image_id()
directly and rename variables for more explicitness.

Before:

  $ rados -p rbd ls | grep rbd_group_header
  rbd_group_header.10256b8b4567
  rbd_group_header.10216b8b4567
  rbd_group_header.10236b8b4567
  rbd_group_header.101f6b8b4567

After:

  $ rados -p rbd ls | grep rbd_group_header
  rbd_group_header.10255f555a5
  rbd_group_header.1023f347eafb
  rbd_group_header.101f24c75111
  rbd_group_header.1021dda4e122

Fixes: https://tracker.ceph.com/issues/65573
Signed-off-by: Ilya Dryomov <[email protected]>

Author: idryomov

src/librbd/Utils.cc

@@ -59,6 +59,7 @@ librados::AioCompletion *create_rados_callback(Context *on_finish) {
   return create_rados_callback<Context, &Context::complete>(on_finish);
 }
 
+// also used for group and group snapshot ids
 std::string generate_image_id(librados::IoCtx &ioctx) {
   librados::Rados rados(ioctx);
 

src/librbd/api/Group.cc

@@ -53,17 +53,6 @@ snap_t get_group_snap_id(I* ictx,
   return CEPH_NOSNAP;
 }
 
-string generate_uuid(librados::IoCtx& io_ctx)
-{
-  Rados rados(io_ctx);
-  uint64_t bid = rados.get_instance_id();
-
-  uint32_t extra = rand() % 0xFFFFFFFF;
-  std::ostringstream bid_ss;
-  bid_ss << std::hex << bid << std::hex << extra;
-  return bid_ss.str();
-}
-
 int group_snap_list(librados::IoCtx& group_ioctx, const char *group_name,
 		    std::vector<cls::rbd::GroupSnapshot> *cls_snaps)
 {
@@ -523,21 +512,20 @@ int Group<I>::create(librados::IoCtx& io_ctx, const char *group_name)
 {
   CephContext *cct = (CephContext *)io_ctx.cct();
 
-  string id = generate_uuid(io_ctx);
-
   ldout(cct, 2) << "adding group to directory..." << dendl;
 
+  std::string group_id = util::generate_image_id(io_ctx);
   int r = cls_client::group_dir_add(&io_ctx, RBD_GROUP_DIRECTORY, group_name,
-                                    id);
+                                    group_id);
   if (r < 0) {
     lderr(cct) << "error adding group to directory: "
 	       << cpp_strerror(r)
 	       << dendl;
     return r;
   }
-  string header_oid = util::group_header_name(id);
 
-  r = io_ctx.create(header_oid, true);
+  std::string group_header_oid = util::group_header_name(group_id);
+  r = io_ctx.create(group_header_oid, true);
   if (r < 0) {
     lderr(cct) << "error creating group header: " << cpp_strerror(r) << dendl;
     goto err_remove_from_dir;
@@ -547,7 +535,7 @@ int Group<I>::create(librados::IoCtx& io_ctx, const char *group_name)
 
 err_remove_from_dir:
   int remove_r = cls_client::group_dir_remove(&io_ctx, RBD_GROUP_DIRECTORY,
-					      group_name, id);
+					      group_name, group_id);
   if (remove_r < 0) {
     lderr(cct) << "error cleaning up group from rbd_directory "
 	       << "object after creation failed: " << cpp_strerror(remove_r)
@@ -929,7 +917,7 @@ int Group<I>::snap_create(librados::IoCtx& group_ioctx,
 
   string group_header_oid = util::group_header_name(group_id);
 
-  group_snap.id = generate_uuid(group_ioctx);
+  group_snap.id = util::generate_image_id(group_ioctx);
   group_snap.name = string(snap_name);
   group_snap.state = cls::rbd::GROUP_SNAPSHOT_STATE_INCOMPLETE;
   group_snap.snaps = image_snaps;