Patchwork monitor: make 'info snapshots' show only fully available snapshots

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Submitter Miguel Di Ciurcio Filho
Date July 27, 2010, 2:54 p.m.
Message ID <1280242448-20775-1-git-send-email-miguel.filho@gmail.com>
Download mbox | patch
Permalink /patch/60007/
State New
Headers show

Comments

Miguel Di Ciurcio Filho - July 27, 2010, 2:54 p.m.
The output generated by 'info snapshots' shows only snapshots that exist on the
block device that saves the VM state. This output can cause an user to
erroneously try to load an snapshot that is not available on all block devices.

$ qemu-img snapshot -l xxtest.qcow2
Snapshot list:
ID        TAG                 VM SIZE                DATE       VM CLOCK
1                                1.5M 2010-07-26 16:51:52   00:00:08.599
2                                1.5M 2010-07-26 16:51:53   00:00:09.719
3                                1.5M 2010-07-26 17:26:49   00:00:13.245
4                                1.5M 2010-07-26 19:01:00   00:00:46.763

$ qemu-img snapshot -l xxtest2.qcow2
Snapshot list:
ID        TAG                 VM SIZE                DATE       VM CLOCK
3                                   0 2010-07-26 17:26:49   00:00:13.245
4                                   0 2010-07-26 19:01:00   00:00:46.763

Current output:
$ qemu -hda xxtest.qcow2 -hdb xxtest2.qcow2 -monitor stdio -vnc :0
QEMU 0.12.4 monitor - type 'help' for more information
(qemu) info snapshots
Snapshot devices: ide0-hd0
Snapshot list (from ide0-hd0):
ID        TAG                 VM SIZE                DATE       VM CLOCK
1                                1.5M 2010-07-26 16:51:52   00:00:08.599
2                                1.5M 2010-07-26 16:51:53   00:00:09.719
3                                1.5M 2010-07-26 17:26:49   00:00:13.245
4                                1.5M 2010-07-26 19:01:00   00:00:46.763

Snapshots 1 and 2 do not exist on xxtest2.qcow, but they are displayed anyway.

This patch sumarizes the output to only show fully available snapshots.

New output:
(qemu) info snapshots
ID        TAG                 VM SIZE                DATE       VM CLOCK
3                                1.5M 2010-07-26 17:26:49   00:00:13.245
4                                1.5M 2010-07-26 19:01:00   00:00:46.763

Signed-off-by: Miguel Di Ciurcio Filho <miguel.filho@gmail.com>
---
 savevm.c |   65 ++++++++++++++++++++++++++++++++++++++++++-------------------
 1 files changed, 45 insertions(+), 20 deletions(-)
Markus Armbruster - July 28, 2010, 3:38 p.m.
Miguel Di Ciurcio Filho <miguel.filho@gmail.com> writes:

> The output generated by 'info snapshots' shows only snapshots that exist on the
> block device that saves the VM state. This output can cause an user to
> erroneously try to load an snapshot that is not available on all block devices.

What happens when you try that?

> $ qemu-img snapshot -l xxtest.qcow2
> Snapshot list:
> ID        TAG                 VM SIZE                DATE       VM CLOCK
> 1                                1.5M 2010-07-26 16:51:52   00:00:08.599
> 2                                1.5M 2010-07-26 16:51:53   00:00:09.719
> 3                                1.5M 2010-07-26 17:26:49   00:00:13.245
> 4                                1.5M 2010-07-26 19:01:00   00:00:46.763
>
> $ qemu-img snapshot -l xxtest2.qcow2
> Snapshot list:
> ID        TAG                 VM SIZE                DATE       VM CLOCK
> 3                                   0 2010-07-26 17:26:49   00:00:13.245
> 4                                   0 2010-07-26 19:01:00   00:00:46.763
>
> Current output:
> $ qemu -hda xxtest.qcow2 -hdb xxtest2.qcow2 -monitor stdio -vnc :0
> QEMU 0.12.4 monitor - type 'help' for more information
> (qemu) info snapshots
> Snapshot devices: ide0-hd0
> Snapshot list (from ide0-hd0):
> ID        TAG                 VM SIZE                DATE       VM CLOCK
> 1                                1.5M 2010-07-26 16:51:52   00:00:08.599
> 2                                1.5M 2010-07-26 16:51:53   00:00:09.719
> 3                                1.5M 2010-07-26 17:26:49   00:00:13.245
> 4                                1.5M 2010-07-26 19:01:00   00:00:46.763
>
> Snapshots 1 and 2 do not exist on xxtest2.qcow, but they are displayed anyway.
>
> This patch sumarizes the output to only show fully available snapshots.
>
> New output:
> (qemu) info snapshots
> ID        TAG                 VM SIZE                DATE       VM CLOCK
> 3                                1.5M 2010-07-26 17:26:49   00:00:13.245
> 4                                1.5M 2010-07-26 19:01:00   00:00:46.763
>
> Signed-off-by: Miguel Di Ciurcio Filho <miguel.filho@gmail.com>

No information on "partial" snapshots.  I doubt anybody will miss it.

> ---
>  savevm.c |   65 ++++++++++++++++++++++++++++++++++++++++++-------------------
>  1 files changed, 45 insertions(+), 20 deletions(-)
>
> diff --git a/savevm.c b/savevm.c
> index 7a1de3c..be83878 100644
> --- a/savevm.c
> +++ b/savevm.c
> @@ -1997,37 +1997,62 @@ void do_delvm(Monitor *mon, const QDict *qdict)
>  
>  void do_info_snapshots(Monitor *mon)
>  {
> -    BlockDriverState *bs, *bs1;
> -    QEMUSnapshotInfo *sn_tab, *sn;
> -    int nb_sns, i;
> +    BlockDriverState *bs_vm_state, *bs;
> +    QEMUSnapshotInfo *sn_tab, *sn, s, *sn_info = &s;
> +    int nb_sns, i, ret, available;
> +    int total;
> +    int *available_snapshots;
>      char buf[256];
>  
> -    bs = bdrv_snapshots();
> -    if (!bs) {
> +    bs_vm_state = bdrv_snapshots();
> +    if (!bs_vm_state) {
>          monitor_printf(mon, "No available block device supports snapshots\n");
>          return;
>      }
> -    monitor_printf(mon, "Snapshot devices:");
> -    bs1 = NULL;
> -    while ((bs1 = bdrv_next(bs1))) {
> -        if (bdrv_can_snapshot(bs1)) {
> -            if (bs == bs1)
> -                monitor_printf(mon, " %s", bdrv_get_device_name(bs1));
> -        }
> -    }
> -    monitor_printf(mon, "\n");
>  
> -    nb_sns = bdrv_snapshot_list(bs, &sn_tab);
> +    nb_sns = bdrv_snapshot_list(bs_vm_state, &sn_tab);
>      if (nb_sns < 0) {
>          monitor_printf(mon, "bdrv_snapshot_list: error %d\n", nb_sns);
>          return;
> +    } else if (nb_sns == 0) {
> +        monitor_printf(mon, "There is no snapshot available.\n");
>      }

This changes output for the "no snapshots available" case from the empty
table

    ID        TAG                 VM SIZE                DATE       VM CLOCK

to

    There is no snapshot available.

I'd prefer that as separate patch, if at all.

Nitpick: I don't like "return; else".

> -    monitor_printf(mon, "Snapshot list (from %s):\n",
> -                   bdrv_get_device_name(bs));
> -    monitor_printf(mon, "%s\n", bdrv_snapshot_dump(buf, sizeof(buf), NULL));
> -    for(i = 0; i < nb_sns; i++) {
> +
> +    available_snapshots = qemu_mallocz(sizeof(int) * nb_sns);

This can die due to the nonsensical semantics of qemu_mallocz(0).

> +    total = 0;
> +    for (i = 0; i < nb_sns; i++) {
>          sn = &sn_tab[i];
> -        monitor_printf(mon, "%s\n", bdrv_snapshot_dump(buf, sizeof(buf), sn));
> +        available = 1;
> +        bs = NULL;
> +
> +        while ((bs = bdrv_next(bs))) {
> +            if (bdrv_can_snapshot(bs) && bs != bs_vm_state) {
> +                ret = bdrv_snapshot_find(bs, sn_info, sn->id_str);
> +                if (ret < 0) {
> +                    available = 0;
> +                    break;
> +                }
> +            }
> +        }
> +
> +        if (available) {
> +            available_snapshots[total] = i;
> +            total++;
> +        }
>      }
> +
> +    if (total > 0) {
> +        monitor_printf(mon, "%s\n", bdrv_snapshot_dump(buf, sizeof(buf), NULL));
> +        for (i = 0; i < total; i++) {
> +            sn = &sn_tab[available_snapshots[i]];
> +            monitor_printf(mon, "%s\n", bdrv_snapshot_dump(buf, sizeof(buf), sn));
> +        }
> +
> +        qemu_free(available_snapshots);
> +
> +    } else {
> +        monitor_printf(mon, "There is no suitable snapshot available to be loaded.\n");

Where is available_snapshots freed when control flows through this point?

> +    }
> +
>      qemu_free(sn_tab);
>  }
Miguel Di Ciurcio Filho - July 28, 2010, 4:37 p.m.
On Wed, Jul 28, 2010 at 12:38 PM, Markus Armbruster <armbru@redhat.com> wrote:
> Miguel Di Ciurcio Filho <miguel.filho@gmail.com> writes:
>
>> The output generated by 'info snapshots' shows only snapshots that exist on the
>> block device that saves the VM state. This output can cause an user to
>> erroneously try to load an snapshot that is not available on all block devices.
>
> What happens when you try that?
>

I've sent a patch that will protect that from happening [1]. With that
patch, the VM stays stopped, without it the VM keeps running with a
failed bdrv_snapshot_goto().

>
>> ---
>>  savevm.c |   65 ++++++++++++++++++++++++++++++++++++++++++-------------------
>>  1 files changed, 45 insertions(+), 20 deletions(-)
>>
>> diff --git a/savevm.c b/savevm.c
>> index 7a1de3c..be83878 100644
>> --- a/savevm.c
>> +++ b/savevm.c
>> @@ -1997,37 +1997,62 @@ void do_delvm(Monitor *mon, const QDict *qdict)
>>
>>  void do_info_snapshots(Monitor *mon)
>>  {
>> -    BlockDriverState *bs, *bs1;
>> -    QEMUSnapshotInfo *sn_tab, *sn;
>> -    int nb_sns, i;
>> +    BlockDriverState *bs_vm_state, *bs;
>> +    QEMUSnapshotInfo *sn_tab, *sn, s, *sn_info = &s;
>> +    int nb_sns, i, ret, available;
>> +    int total;
>> +    int *available_snapshots;
>>      char buf[256];
>>
>> -    bs = bdrv_snapshots();
>> -    if (!bs) {
>> +    bs_vm_state = bdrv_snapshots();
>> +    if (!bs_vm_state) {
>>          monitor_printf(mon, "No available block device supports snapshots\n");
>>          return;
>>      }
>> -    monitor_printf(mon, "Snapshot devices:");
>> -    bs1 = NULL;
>> -    while ((bs1 = bdrv_next(bs1))) {
>> -        if (bdrv_can_snapshot(bs1)) {
>> -            if (bs == bs1)
>> -                monitor_printf(mon, " %s", bdrv_get_device_name(bs1));
>> -        }
>> -    }
>> -    monitor_printf(mon, "\n");
>>
>> -    nb_sns = bdrv_snapshot_list(bs, &sn_tab);
>> +    nb_sns = bdrv_snapshot_list(bs_vm_state, &sn_tab);
>>      if (nb_sns < 0) {
>>          monitor_printf(mon, "bdrv_snapshot_list: error %d\n", nb_sns);
>>          return;
>> +    } else if (nb_sns == 0) {
>> +        monitor_printf(mon, "There is no snapshot available.\n");
>>      }
>
> This changes output for the "no snapshots available" case from the empty
> table
>
>    ID        TAG                 VM SIZE                DATE       VM CLOCK
>
> to
>
>    There is no snapshot available.
>
> I'd prefer that as separate patch, if at all.

I think a clear message saying "there is nothing" is better than an
empty table. I'm already changing the output to something more
reasonable, so.

>
> Nitpick: I don't like "return; else".
>

Yeah, kinda ugly. I will fix it.

>> -    monitor_printf(mon, "Snapshot list (from %s):\n",
>> -                   bdrv_get_device_name(bs));
>> -    monitor_printf(mon, "%s\n", bdrv_snapshot_dump(buf, sizeof(buf), NULL));
>> -    for(i = 0; i < nb_sns; i++) {
>> +
>> +    available_snapshots = qemu_mallocz(sizeof(int) * nb_sns);
>
> This can die due to the nonsensical semantics of qemu_mallocz(0).
>

Will fix that, so this code will be reached only if  nb_sns > 0 and
qemu_mallocz(0) will never be executed.

>> +    total = 0;
>> +    for (i = 0; i < nb_sns; i++) {
>>          sn = &sn_tab[i];
>> -        monitor_printf(mon, "%s\n", bdrv_snapshot_dump(buf, sizeof(buf), sn));
>> +        available = 1;
>> +        bs = NULL;
>> +
>> +        while ((bs = bdrv_next(bs))) {
>> +            if (bdrv_can_snapshot(bs) && bs != bs_vm_state) {
>> +                ret = bdrv_snapshot_find(bs, sn_info, sn->id_str);
>> +                if (ret < 0) {
>> +                    available = 0;
>> +                    break;
>> +                }
>> +            }
>> +        }
>> +
>> +        if (available) {
>> +            available_snapshots[total] = i;
>> +            total++;
>> +        }
>>      }
>> +
>> +    if (total > 0) {
>> +        monitor_printf(mon, "%s\n", bdrv_snapshot_dump(buf, sizeof(buf), NULL));
>> +        for (i = 0; i < total; i++) {
>> +            sn = &sn_tab[available_snapshots[i]];
>> +            monitor_printf(mon, "%s\n", bdrv_snapshot_dump(buf, sizeof(buf), sn));
>> +        }
>> +
>> +        qemu_free(available_snapshots);
>> +
>> +    } else {
>> +        monitor_printf(mon, "There is no suitable snapshot available to be loaded.\n");
>
> Where is available_snapshots freed when control flows through this point?
>

Oops. I will fix that too.

Thanks for the feedback.

Regards,

Miguel

[1] http://lists.gnu.org/archive/html/qemu-devel/2010-07/msg01065.html
(Kevin has applied it to this block branch)

Patch

diff --git a/savevm.c b/savevm.c
index 7a1de3c..be83878 100644
--- a/savevm.c
+++ b/savevm.c
@@ -1997,37 +1997,62 @@  void do_delvm(Monitor *mon, const QDict *qdict)
 
 void do_info_snapshots(Monitor *mon)
 {
-    BlockDriverState *bs, *bs1;
-    QEMUSnapshotInfo *sn_tab, *sn;
-    int nb_sns, i;
+    BlockDriverState *bs_vm_state, *bs;
+    QEMUSnapshotInfo *sn_tab, *sn, s, *sn_info = &s;
+    int nb_sns, i, ret, available;
+    int total;
+    int *available_snapshots;
     char buf[256];
 
-    bs = bdrv_snapshots();
-    if (!bs) {
+    bs_vm_state = bdrv_snapshots();
+    if (!bs_vm_state) {
         monitor_printf(mon, "No available block device supports snapshots\n");
         return;
     }
-    monitor_printf(mon, "Snapshot devices:");
-    bs1 = NULL;
-    while ((bs1 = bdrv_next(bs1))) {
-        if (bdrv_can_snapshot(bs1)) {
-            if (bs == bs1)
-                monitor_printf(mon, " %s", bdrv_get_device_name(bs1));
-        }
-    }
-    monitor_printf(mon, "\n");
 
-    nb_sns = bdrv_snapshot_list(bs, &sn_tab);
+    nb_sns = bdrv_snapshot_list(bs_vm_state, &sn_tab);
     if (nb_sns < 0) {
         monitor_printf(mon, "bdrv_snapshot_list: error %d\n", nb_sns);
         return;
+    } else if (nb_sns == 0) {
+        monitor_printf(mon, "There is no snapshot available.\n");
     }
-    monitor_printf(mon, "Snapshot list (from %s):\n",
-                   bdrv_get_device_name(bs));
-    monitor_printf(mon, "%s\n", bdrv_snapshot_dump(buf, sizeof(buf), NULL));
-    for(i = 0; i < nb_sns; i++) {
+
+    available_snapshots = qemu_mallocz(sizeof(int) * nb_sns);
+    total = 0;
+    for (i = 0; i < nb_sns; i++) {
         sn = &sn_tab[i];
-        monitor_printf(mon, "%s\n", bdrv_snapshot_dump(buf, sizeof(buf), sn));
+        available = 1;
+        bs = NULL;
+
+        while ((bs = bdrv_next(bs))) {
+            if (bdrv_can_snapshot(bs) && bs != bs_vm_state) {
+                ret = bdrv_snapshot_find(bs, sn_info, sn->id_str);
+                if (ret < 0) {
+                    available = 0;
+                    break;
+                }
+            }
+        }
+
+        if (available) {
+            available_snapshots[total] = i;
+            total++;
+        }
     }
+
+    if (total > 0) {
+        monitor_printf(mon, "%s\n", bdrv_snapshot_dump(buf, sizeof(buf), NULL));
+        for (i = 0; i < total; i++) {
+            sn = &sn_tab[available_snapshots[i]];
+            monitor_printf(mon, "%s\n", bdrv_snapshot_dump(buf, sizeof(buf), sn));
+        }
+
+        qemu_free(available_snapshots);
+
+    } else {
+        monitor_printf(mon, "There is no suitable snapshot available to be loaded.\n");
+    }
+
     qemu_free(sn_tab);
 }