Re: [Qemu-devel] [PATCH COLO-Frame v16 23/35] COLO failover: Don't do failover during loading VM's state

[Changlong Xie]

On 04/08/2016 02:26 PM, zhanghailiang wrote:
We should not do failover work while the main thread is loading
VM's state, otherwise it will destroy the consistent of VM's memory and
device state.
Here we add a new failover status 'RELAUNCH' which means we should
relaunch the process of failover.

Signed-off-by: zhanghailiang <zhang.zhanghaili...@huawei.com>
Signed-off-by: Li Zhijian <lizhij...@cn.fujitsu.com>
Reviewed-by: Dr. David Alan Gilbert <dgilb...@redhat.com>
---
v14:
- Move the place of 'vmstate_loading = false;'.
v13:
- Add Reviewed-by tag
---
  include/migration/failover.h |  2 ++
  migration/colo.c             | 25 +++++++++++++++++++++++++
  2 files changed, 27 insertions(+)

diff --git a/include/migration/failover.h b/include/migration/failover.h
index c4bd81e..99b0d58 100644
--- a/include/migration/failover.h
+++ b/include/migration/failover.h
@@ -20,6 +20,8 @@ typedef enum COLOFailoverStatus {
      FAILOVER_STATUS_REQUEST = 1, /* Request but not handled */
      FAILOVER_STATUS_HANDLING = 2, /* In the process of handling failover */
      FAILOVER_STATUS_COMPLETED = 3, /* Finish the failover process */
+    /* Optional, Relaunch the failover process, again 'NONE' -> 'COMPLETED' */
+    FAILOVER_STATUS_RELAUNCH = 4,
  } COLOFailoverStatus;

  void failover_init_state(void);
diff --git a/migration/colo.c b/migration/colo.c
index c4989c6..252a290 100644
--- a/migration/colo.c
+++ b/migration/colo.c
@@ -20,6 +20,8 @@
  #include "migration/failover.h"
  #include "qapi-event.h"

+static bool vmstate_loading;
+
  /* colo buffer */
  #define COLO_BUFFER_BASE_SIZE (4 * 1024 * 1024)

@@ -52,6 +54,19 @@ static void secondary_vm_do_failover(void)
      int old_state;
      MigrationIncomingState *mis = migration_incoming_get_current();

+    /* Can not do failover during the process of VM's loading VMstate, Or
+      * it will break the secondary VM.

Wrong comments style

+      */
+    if (vmstate_loading) {
+        old_state = failover_set_state(FAILOVER_STATUS_HANDLING,
+                                       FAILOVER_STATUS_RELAUNCH);
+        if (old_state != FAILOVER_STATUS_HANDLING) {
+            error_report("Unknown error while do failover for secondary VM,"
+                         "old_state: %d", old_state);
+        }
+        return;
+    }
+
      migrate_set_state(&mis->state, MIGRATION_STATUS_COLO,
                        MIGRATION_STATUS_COMPLETED);

@@ -561,13 +576,22 @@ void *colo_process_incoming_thread(void *opaque)

          qemu_mutex_lock_iothread();
          qemu_system_reset(VMRESET_SILENT);
+        vmstate_loading = true;
          if (qemu_loadvm_state(fb) < 0) {
              error_report("COLO: loadvm failed");
              qemu_mutex_unlock_iothread();
              goto out;
          }
+
+        vmstate_loading = false;
          qemu_mutex_unlock_iothread();

+        if (failover_get_state() == FAILOVER_STATUS_RELAUNCH) {
+            failover_set_state(FAILOVER_STATUS_RELAUNCH, FAILOVER_STATUS_NONE);
+            failover_request_active(NULL);
+            goto out;
+        }
+
          colo_send_message(mis->to_src_file, COLO_MESSAGE_VMSTATE_LOADED,
                       &local_err);
          if (local_err) {
@@ -579,6 +603,7 @@ void *colo_process_incoming_thread(void *opaque)
      }

  out:
+     vmstate_loading = false;

An redundant blank.

It seems there are many coding style issues in whole colo.c that you 
did't notice.

Thanks
        -Xie

      /* Throw the unreported error message after exited from loop */
      if (local_err) {
          error_report_err(local_err);