Re: [Qemu-devel] [PATCH] savevm: create snapshot failed when id_str already exits

[Stefan Hajnoczi]

On Thu, Mar 05, 2015 at 09:05:52PM +0800, Yi Wang wrote:
> Thanks for your reply and Happy Lantern Festival!
> I am afraid you misunderstood what I mean, maybe I didn't express
> clearly :-) My patch works in such case:
> Firstly vm has two disks:
> [root@fox-host vmimg]# virsh domblklist win7
> Target Source
> ------------------------------------------------
> hdb /home/virtio_test.iso
> vda /home/vmimg/win7.img.1
> vdb /home/vmimg/win7.append
> 
> Secondly first disk has one snapshot with id_str "1", and another disk
> has three snapshots with id_str "1", "2", "3".
> [root@fox-host vmimg]# qemu-img snapshot -l win7.img.1
> Snapshot list:
> ID TAG VM SIZE DATE VM CLOCK
> 1 s1 0 2015-03-05 10:26:16 00:00:00.000
> 
> [root@fox-host vmimg]# qemu-img snapshot -l win7.append
> Snapshot list:
> ID TAG VM SIZE DATE VM CLOCK
> 1 s3 0 2015-03-05 10:29:21 00:00:00.000
> 2 s1 0 2015-03-05 10:29:38 00:00:00.000
> 3 s2 0 2015-03-05 10:30:49 00:00:00.000
> 
> In this case, we will fail when create snapshot specifying a name,
> 'cause id_str "2" already exists in disk vdb.
> [root@fox-host8 vmimg]# virsh snapshot-create-as win7-fox s4
> error: operation failed: Failed to take snapshot: Error while creating
> snapshot on 'drive-virtio-disk1'

This means that name != NULL but it is still unnecessary to duplicate ID
generation.

Does this work?

diff --git a/savevm.c b/savevm.c
index 08ec678..e81e4aa 100644
--- a/savevm.c
+++ b/savevm.c
@@ -1047,6 +1047,7 @@ void do_savevm(Monitor *mon, const QDict *qdict)
     QEMUFile *f;
     int saved_vm_running;
     uint64_t vm_state_size;
+    bool generate_ids = true;
     qemu_timeval tv;
     struct tm tm;
     const char *name = qdict_get_try_str(qdict, "name");
@@ -1088,6 +1089,7 @@ void do_savevm(Monitor *mon, const QDict *qdict)
         if (ret >= 0) {
             pstrcpy(sn->name, sizeof(sn->name), old_sn->name);
             pstrcpy(sn->id_str, sizeof(sn->id_str), old_sn->id_str);
+            generate_ids = false;
         } else {
             pstrcpy(sn->name, sizeof(sn->name), name);
         }
@@ -1123,6 +1125,14 @@ void do_savevm(Monitor *mon, const QDict *qdict)
         if (bdrv_can_snapshot(bs1)) {
             /* Write VM state size only to the image that contains the state */
             sn->vm_state_size = (bs == bs1 ? vm_state_size : 0);
+
+            /* Images may have existing IDs so let the ID be autogenerated if 
the
+             * user did not specify a name.
+             */
+            if (generate_ids) {
+                sn->id_str[0] = '\0';
+            }
+
             ret = bdrv_snapshot_create(bs1, sn);
             if (ret < 0) {
                 monitor_printf(mon, "Error while creating snapshot on '%s'\n",

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