[libvirt] [PATCH] snapshot: allow reuse of existing files in disk snapshot

[Eric Blake]

On 01/10/2012 10:15 AM, Peter Krempa wrote:
> On 01/09/2012 08:03 PM, Eric Blake wrote:
>> When disk snapshots were first implemented, libvirt blindly refused
>> to allow an external snapshot destination that already exists, since
>> qemu will blindly overwrite the contents of that file during the
>> snapshot_blkdev monitor command, and we don't like a default of
>> data loss by default.  But VDSM has a scenario where NFS permissions
>> are intentionally set so that the destination file can only be
>> created by the management machine, and not the machine where the
>> guest is running, so that libvirt will necessarily see the destination
>> file already existing; adding a flag will allow VDSM to force the file
>> reuse without libvirt complaining of possible data loss.
>>

>> +    VIR_DOMAIN_SNAPSHOT_CREATE_REUSE_EXT   = (1<<  5), /* reuse any
>> existing
>> +                                                          external
>> files */
>>   } virDomainSnapshotCreateFlags;
> 
> You added a new flag here
> 
>>
>>   /* Take a snapshot of the current VM state */
>> diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
>> index 1a7e816..9765a69 100644
>> --- a/src/qemu/qemu_driver.c
>> +++ b/src/qemu/qemu_driver.c
>> @@ -10162,11 +10163,14 @@ qemuDomainSnapshotCreateXML(virDomainPtr
>> domain,
> 
> --- SNIP from top of this func. ------
>     virCheckFlags(VIR_DOMAIN_SNAPSHOT_CREATE_REDEFINE |
>                   VIR_DOMAIN_SNAPSHOT_CREATE_CURRENT |
>                   VIR_DOMAIN_SNAPSHOT_CREATE_NO_METADATA |
>                   VIR_DOMAIN_SNAPSHOT_CREATE_HALT |
>                   VIR_DOMAIN_SNAPSHOT_CREATE_DISK_ONLY, NULL);
> ----- </snip> -----------
> 
> But you don't check for the new flag here.

Oops - shows that I posted before testing.  Now fixed.

> 
> Apart from that I think the code looks sane. ACK with that flag check
> fixed.

Thanks; pushed (after testing, this time).

-- 
Eric Blake   eblake at redhat.com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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