[Qemu-devel] [PATCH 07/11] migration: reorder processing in hmp_savevm

["Denis V. Lunev" <den@openvz.org>]

This approach looks a bit more natural.

State deletion can be performed on running VM which reduces VM downtime

The situation when we have all devices read-only is not that frequent
to optimize for it. We can afford to pause VM for the case. This reduces
the amount of time when aio_context remains locked with next patches.

Signed-off-by: Denis V. Lunev <den@openvz.org>
CC: Juan Quintela <quintela@redhat.com>
---
 migration/savevm.c | 24 ++++++++++++------------
 1 file changed, 12 insertions(+), 12 deletions(-)

diff --git a/migration/savevm.c b/migration/savevm.c
index f7ff37a..dbcb313 100644
--- a/migration/savevm.c
+++ b/migration/savevm.c
@@ -1267,9 +1267,12 @@ void hmp_savevm(Monitor *mon, const QDict *qdict)
         return;
     }
 
-    bs = find_vmstate_bs();
-    if (!bs) {
-        monitor_printf(mon, "No block device can accept snapshots\n");
+    /* Delete old snapshots of the same name */
+    if (name && bdrv_all_delete_snapshot(name, &bs, &local_err) < 0) {
+        monitor_printf(mon,
+                       "Error while deleting snapshot on device '%s': %s\n",
+                       bdrv_get_device_name(bs), error_get_pretty(local_err));
+        error_free(local_err);
         return;
     }
 
@@ -1290,6 +1293,12 @@ void hmp_savevm(Monitor *mon, const QDict *qdict)
     sn->date_nsec = tv.tv_usec * 1000;
     sn->vm_clock_nsec = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL);
 
+    bs = find_vmstate_bs();
+    if (!bs) {
+        monitor_printf(mon, "No block device can accept snapshots\n");
+        goto the_end;
+    }
+
     if (name) {
         ret = bdrv_snapshot_find(bs, old_sn, name);
         if (ret >= 0) {
@@ -1304,15 +1313,6 @@ void hmp_savevm(Monitor *mon, const QDict *qdict)
         strftime(sn->name, sizeof(sn->name), "vm-%Y%m%d%H%M%S", &tm);
     }
 
-    /* Delete old snapshots of the same name */
-    if (name && bdrv_all_delete_snapshot(name, &bs1, &local_err) < 0) {
-        monitor_printf(mon,
-                       "Error while deleting snapshot on device '%s': %s\n",
-                       bdrv_get_device_name(bs1), error_get_pretty(local_err));
-        error_free(local_err);
-        goto the_end;
-    }
-
     /* save the VM state */
     f = qemu_fopen_bdrv(bs, 1);
     if (!f) {
-- 
2.5.0