rbd-mirror: group-replayer check for remote demote state

I'm seeing a possibility for 3 situations here for resync flagging and
rbd-mirror daemon working on it:

1. No Demotion on Primary while/just-before resync is play'ed
    there is no demote snap along side resync, we can cancel syncing other
    snaps, and start resync as soon as resync is flagged, because there is
    no point syncing snaps that we are anyway going to delete the whole
    group and resync fresh.

2. first Demote + immediately Resync
    demote came first, this mean before proceeding with resync, we should
    always see if the last remote snap is PRIMARY (validate if the remote
    is still primary, which is on point) and only proceed

3. first Resync + immediately Demote
    resync Came first, so we head straight to resync.

Signed-off-by: Prasanna Kumar Kalever <prasanna.kalever@redhat.com>

diff --git a/src/tools/rbd_mirror/group_replayer/Replayer.cc b/src/tools/rbd_mirror/group_replayer/Replayer.cc
index 63c2f097e9730f8f959ac803fcbba88538b40fd8..2fe96e8bba639edadc00b2ddf4c6d1e1a3d9ec68 100644 (file)
--- a/src/tools/rbd_mirror/group_replayer/Replayer.cc
+++ b/src/tools/rbd_mirror/group_replayer/Replayer.cc
@@ -270,12 +270,6 @@ void Replayer<I>::load_local_group_snapshots() {
 
     if (m_stop_requested) {
       return;
-    } else if (is_resync_requested()) {
-      m_stop_requested = true;
-      dout(10) << "local group resync requested" << dendl;
-      // send stop for Group Replayer
-      notify_group_listener_stop();
-      return;
     } else if (is_rename_requested()) {
       m_stop_requested = true;
       dout(10) << "remote group rename requested" << dendl;
@@ -378,22 +372,35 @@ void Replayer<I>::handle_load_remote_group_snapshots(int r) {
   }
   m_in_flight_op_tracker.finish_op();
 
+  auto last_local_snap = m_local_group_snaps.rbegin();
+  auto last_remote_snap = m_remote_group_snaps.rbegin();
   if (r < 0) {  // may be remote group is deleted?
     derr << "error listing remote mirror group snapshots: " << cpp_strerror(r)
          << dendl;
     notify_group_listener_stop();
     return;
+  } else if (is_resync_requested()) {
+    dout(10) << "local group resync requested" << dendl;
+    auto last_remote_snap_ns = std::get_if<cls::rbd::GroupSnapshotNamespaceMirror>(
+        &last_remote_snap->snapshot_namespace);
+    if (last_remote_snap_ns &&
+        last_remote_snap_ns->state == cls::rbd::MIRROR_SNAPSHOT_STATE_PRIMARY) {
+      m_stop_requested = true;
+      // send stop for Group Replayer
+      notify_group_listener_stop();
+      return;
+    }
+    dout(10) << "turns out remote is not primary, we cannot resync, will retry later"
+             << dendl;
   }
 
   if (!m_local_group_snaps.empty()) {
-    auto last_local_snap = m_local_group_snaps.rbegin();
     unlink_group_snapshots(last_local_snap->id);
     auto last_local_snap_ns = std::get_if<cls::rbd::GroupSnapshotNamespaceMirror>(
         &last_local_snap->snapshot_namespace);
     if (last_local_snap_ns &&
         last_local_snap_ns->state == cls::rbd::MIRROR_SNAPSHOT_STATE_NON_PRIMARY_DEMOTED &&
         !m_remote_group_snaps.empty()) {
-      auto last_remote_snap = m_remote_group_snaps.rbegin();
       if (last_local_snap->id == last_remote_snap->id) {
         m_stop_requested = true;
         notify_group_listener_stop();