[Qemu-devel] [PATCH 05/11] migration: move vm_old_running into global state

[Peter Xu <peterx@redhat.com>]

Firstly, it was passed around.  Let's just move it into MigrationState
just like many other variables as state of migration.

One thing to mention is that for postcopy, we actually don't need this
knowledge at all since postcopy can't resume a VM even if it fails (we
can see that from the old code too: when we try to resume we also check
against "entered_postcopy" variable).  So further we do this:

- in postcopy_start(), we don't update vm_old_running since useless
- in migration_thread(), we don't need to check entered_postcopy when
  resume, since it's only used for precopy.

Comment this out too for that variable definition.

Signed-off-by: Peter Xu <peterx@redhat.com>
---
 migration/migration.c | 17 +++++++----------
 migration/migration.h |  6 ++++++
 2 files changed, 13 insertions(+), 10 deletions(-)

diff --git a/migration/migration.c b/migration/migration.c
index b684c2005d..62b3766852 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -1272,6 +1272,7 @@ MigrationState *migrate_init(void)
 
     s->mig_start_time = qemu_clock_get_ms(QEMU_CLOCK_REALTIME);
     s->mig_total_time = 0;
+    s->old_vm_running = false;
     return s;
 }
 
@@ -1846,7 +1847,7 @@ static int await_return_path_close_on_source(MigrationState *ms)
  * Switch from normal iteration to postcopy
  * Returns non-0 on error
  */
-static int postcopy_start(MigrationState *ms, bool *old_vm_running)
+static int postcopy_start(MigrationState *ms)
 {
     int ret;
     QIOChannelBuffer *bioc;
@@ -1864,7 +1865,6 @@ static int postcopy_start(MigrationState *ms, bool *old_vm_running)
     trace_postcopy_start_set_run();
 
     qemu_system_wakeup_request(QEMU_WAKEUP_REASON_OTHER);
-    *old_vm_running = runstate_is_running();
     global_state_store();
     ret = vm_stop_force_state(RUN_STATE_FINISH_MIGRATE);
     if (ret < 0) {
@@ -2055,11 +2055,9 @@ static int migration_maybe_pause(MigrationState *s,
  *
  * @s: Current migration state
  * @current_active_state: The migration state we expect to be in
- * @*old_vm_running: Pointer to old_vm_running flag
  * @*start_time: Pointer to time to update
  */
 static void migration_completion(MigrationState *s, int current_active_state,
-                                 bool *old_vm_running,
                                  int64_t *start_time)
 {
     int ret;
@@ -2068,7 +2066,7 @@ static void migration_completion(MigrationState *s, int current_active_state,
         qemu_mutex_lock_iothread();
         *start_time = qemu_clock_get_ms(QEMU_CLOCK_REALTIME);
         qemu_system_wakeup_request(QEMU_WAKEUP_REASON_OTHER);
-        *old_vm_running = runstate_is_running();
+        s->old_vm_running = runstate_is_running();
         ret = global_state_store();
 
         if (!ret) {
@@ -2174,7 +2172,6 @@ static void *migration_thread(void *opaque)
     int64_t threshold_size = 0;
     int64_t start_time = initial_time;
     int64_t end_time;
-    bool old_vm_running = false;
     bool entered_postcopy = false;
     /* The active state we expect to be in; ACTIVE or POSTCOPY_ACTIVE */
     enum MigrationStatus current_active_state = MIGRATION_STATUS_ACTIVE;
@@ -2233,7 +2230,7 @@ static void *migration_thread(void *opaque)
                     pend_nonpost <= threshold_size &&
                     atomic_read(&s->start_postcopy)) {
 
-                    if (!postcopy_start(s, &old_vm_running)) {
+                    if (!postcopy_start(s)) {
                         current_active_state = MIGRATION_STATUS_POSTCOPY_ACTIVE;
                         entered_postcopy = true;
                     }
@@ -2245,7 +2242,7 @@ static void *migration_thread(void *opaque)
             } else {
                 trace_migration_thread_low_pending(pending_size);
                 migration_completion(s, current_active_state,
-                                     &old_vm_running, &start_time);
+                                     &start_time);
                 break;
             }
         }
@@ -2311,9 +2308,9 @@ static void *migration_thread(void *opaque)
             * Fixme: we will run VM in COLO no matter its old running state.
             * After exited COLO, we will keep running.
             */
-            old_vm_running = true;
+            s->old_vm_running = true;
         }
-        if (old_vm_running && !entered_postcopy) {
+        if (s->old_vm_running) {
             vm_start();
         } else {
             if (runstate_check(RUN_STATE_FINISH_MIGRATE)) {
diff --git a/migration/migration.h b/migration/migration.h
index ac74a12713..0f5df2367c 100644
--- a/migration/migration.h
+++ b/migration/migration.h
@@ -111,6 +111,12 @@ struct MigrationState
     int64_t expected_downtime;
     bool enabled_capabilities[MIGRATION_CAPABILITY__MAX];
     int64_t setup_time;
+    /*
+     * Whether the old VM is running for the last migration.  This is
+     * used to resume the VM when precopy failed or cancelled somehow.
+     * It's never used for postcopy.
+     */
+    bool old_vm_running;
 
     /* Flag set once the migration has been asked to enter postcopy */
     bool start_postcopy;
-- 
2.14.3