[PATCH v3 3/4] migration: Add a semaphore to count PONGs

[Peter Xu <peterx@redhat.com>]

This is mostly useless, but useful for us to know whether the main channel
is correctly established without changing the migration protocol.

Signed-off-by: Peter Xu <peterx@redhat.com>
---
 migration/migration.c | 3 +++
 migration/migration.h | 6 ++++++
 2 files changed, 9 insertions(+)

diff --git a/migration/migration.c b/migration/migration.c
index fb0ecf5649..a2e362541d 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -3025,6 +3025,7 @@ retry:
         case MIG_RP_MSG_PONG:
             tmp32 = ldl_be_p(buf);
             trace_source_return_path_thread_pong(tmp32);
+            qemu_sem_post(&ms->rp_state.rp_pong_acks);
             break;
 
         case MIG_RP_MSG_REQ_PAGES:
@@ -4524,6 +4525,7 @@ static void migration_instance_finalize(Object *obj)
     qemu_sem_destroy(&ms->postcopy_pause_sem);
     qemu_sem_destroy(&ms->postcopy_pause_rp_sem);
     qemu_sem_destroy(&ms->rp_state.rp_sem);
+    qemu_sem_destroy(&ms->rp_state.rp_pong_acks);
     qemu_sem_destroy(&ms->postcopy_qemufile_src_sem);
     error_free(ms->error);
 }
@@ -4570,6 +4572,7 @@ static void migration_instance_init(Object *obj)
     qemu_sem_init(&ms->postcopy_pause_sem, 0);
     qemu_sem_init(&ms->postcopy_pause_rp_sem, 0);
     qemu_sem_init(&ms->rp_state.rp_sem, 0);
+    qemu_sem_init(&ms->rp_state.rp_pong_acks, 0);
     qemu_sem_init(&ms->rate_limit_sem, 0);
     qemu_sem_init(&ms->wait_unplug_sem, 0);
     qemu_sem_init(&ms->postcopy_qemufile_src_sem, 0);
diff --git a/migration/migration.h b/migration/migration.h
index c351872360..4cb1cb6fa8 100644
--- a/migration/migration.h
+++ b/migration/migration.h
@@ -276,6 +276,12 @@ struct MigrationState {
          */
         bool          rp_thread_created;
         QemuSemaphore rp_sem;
+        /*
+         * We post to this when we got one PONG from dest. So far it's an
+         * easy way to know the main channel has successfully established
+         * on dest QEMU.
+         */
+        QemuSemaphore rp_pong_acks;
     } rp_state;
 
     double mbps;
-- 
2.37.3