Re: [Qemu-devel] [PATCH] monitor: make 'info snapshots' show only fully available snapshots

[Markus Armbruster]

Miguel Di Ciurcio Filho <address@hidden> 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 <address@hidden>

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);
>  }