[libvirt] RFC backup API

[Maxim Nestratov]

23.03.2016 17:27, John Snow пишет:
>
> On 03/23/2016 06:36 AM, Kashyap Chamarthy wrote:
>> On Mon, Mar 21, 2016 at 01:18:19PM +0300, Maxim Nestratov wrote:
>>> Hi all,
>>>
>>> It's been already quite a long time since qemu implemented QMP
>>> "drive-backup" command to create block devices backups. Even more,
>>> since qemu 2.4 there is a possibility to create incremental backups.
>>> Though it is possible to backup all attached to a domain disk drives
>>> by combining them into a single QMP transaction command, this way of
>>> creating them, not to mention managing, remains inconvenient for an
>>> end user of libvirt. Moreover, creating a single drive backup via QMP
>>> interface isn't handy either. That said, it looks reasonable to
>>> introduce a *new backup API* based on QMP "drive-backup" facilities.
>> There's also the 'blockdev-backup' command, which seems similar in
>> operation to 'drive-backup', but differs subtly.
>>
>> Looking at qmp-commands.hx, I learn that 'blockdev-backup' accepts
>> target ID; while 'drive-backup' accept target drive name, otherwise,
>> their operation look almost identical, and both commands use
>> backup_start() (from qemu/blockdev.c).  [Added John Snow in CC to
>> correct me if I'm wrong.]
>>
> No, you're right. Blockdev-backup can backup to an arbitrary device
> (which can be backed by a new file), but drive-backup will only accept a
> new file.
>
> I don't think blockdev-backup supports incremental backups just yet, but
> I don't think there's any reason it can't. (Looking at it: yeah, why
> have I not done that yet?...)

John,
Any chances to get this implemented? Just not to use two different 
commands in libvirt and start using 'blockdev-backup' right away for 
both full and incremental backups?

>> For 'blockdev-backup'
>> ---------------------
>>
>> -> { "execute": "blockdev-backup", "arguments": { "device": "src-id",
>>                                                    "sync": "full",
>>                                                    "target": "tgt-id" } }
>> <- { "return": {} }
>>
>>
>> Where 'tagert' in this case means:
>>
>>      "the name of the backup target device. (json-string)"
>>
>>
>> For 'drive-backup'
>> -----------------
>>
>> -> { "execute": "drive-backup", "arguments": { "device": "drive0",
>>                                                 "sync": "full",
>>                                                 "target": "backup.img" } }
>> <- { "return": {} }
>>
>> Here, 'target' means:
>>
>>          "the target of the new image. If the file exists, or if it is a
>>          device, the existing file/device will be used as the new
>>          destination.  If it does not exist, a new file will be created.
>>          (json-string)"
>>
>> [...]
>>
>>
> --js