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Re: [Qemu-devel] [Qemu-block] [PATCH v10 08/10] Implement new driver for
From: |
Wen Congyang |
Subject: |
Re: [Qemu-devel] [Qemu-block] [PATCH v10 08/10] Implement new driver for block replication |
Date: |
Fri, 16 Oct 2015 08:52:01 +0800 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.2.0 |
On 10/15/2015 10:55 PM, Stefan Hajnoczi wrote:
> On Thu, Oct 15, 2015 at 10:19:17AM +0800, Wen Congyang wrote:
>> On 10/14/2015 10:27 PM, Stefan Hajnoczi wrote:
>>> On Tue, Oct 13, 2015 at 05:08:17PM +0800, Wen Congyang wrote:
>>>> On 10/13/2015 12:27 AM, Stefan Hajnoczi wrote:
>>>>> On Fri, Sep 25, 2015 at 02:17:36PM +0800, Wen Congyang wrote:
>>>>>> + /* start backup job now */
>>>>>> + bdrv_op_unblock(s->hidden_disk, BLOCK_OP_TYPE_BACKUP_TARGET,
>>>>>> + s->active_disk->backing_blocker);
>>>>>> + bdrv_op_unblock(s->secondary_disk, BLOCK_OP_TYPE_BACKUP_SOURCE,
>>>>>> + s->hidden_disk->backing_blocker);
>>>>>
>>>>> Why is it safe to unblock these operations?
>>>>>
>>>>> Why do they have to be blocked for non-replication users?
>>>>
>>>> hidden_disk and secondary disk are opened as backing file, so it is
>>>> blocked for
>>>> non-replication users.
>>>> What can I do if I don't unblock it and want to do backup?
>>>
>>> CCing Jeff Cody, block jobs maintainer
>>>
>>> You need to explain why it is safe remove this protection. We can't
>>> merge code that may be unsafe.
>>>
>>> I think we can investigate further by asking: when does QEMU code assume
>>> the backing file is read-only?
>>
>> The backing file is opened in read-only mode. I want to reopen it in
>> read-write
>> mode here in the next version(So the patch 1 will be dropped)
>>
>>>
>>> I haven't checked but these cases come to mind:
>>>
>>> Operations that move data between BDS in the backing chain (e.g. commit
>>> and stream block jobs) will lose or overwrite data if the backing file
>>> is being written to by another coroutine.
>>>
>>> We need to prevent users from running these operations at the same time.
>>
>> Yes, but qemu doesn't provide such API.
>
> This series can't be merged unless it is safe.
>
> Have you looked at op blockers and thought about how to prevent unsafe
> operations?
Hmm, only block jobs will write to the backing file? If so, op blockers can
prevent unsafe operations.
Thanks
Wen Congyang
>
> Stefan
> .
>
- Re: [Qemu-devel] [Qemu-block] [PATCH v10 08/10] Implement new driver for block replication, (continued)
Re: [Qemu-devel] [Qemu-block] [PATCH v10 08/10] Implement new driver for block replication, Stefan Hajnoczi, 2015/10/12
- Re: [Qemu-devel] [Qemu-block] [PATCH v10 08/10] Implement new driver for block replication, Wen Congyang, 2015/10/15
- Re: [Qemu-devel] [Qemu-block] [PATCH v10 08/10] Implement new driver for block replication, Stefan Hajnoczi, 2015/10/15
- Re: [Qemu-devel] [Qemu-block] [PATCH v10 08/10] Implement new driver for block replication, Wen Congyang, 2015/10/14
- Re: [Qemu-devel] [Qemu-block] [PATCH v10 08/10] Implement new driver for block replication, Stefan Hajnoczi, 2015/10/15
- Re: [Qemu-devel] [Qemu-block] [PATCH v10 08/10] Implement new driver for block replication,
Wen Congyang <=
- Re: [Qemu-devel] [Qemu-block] [PATCH v10 08/10] Implement new driver for block replication, Wen Congyang, 2015/10/16
- Re: [Qemu-devel] [Qemu-block] [PATCH v10 08/10] Implement new driver for block replication, Stefan Hajnoczi, 2015/10/16
- Re: [Qemu-devel] [Qemu-block] [PATCH v10 08/10] Implement new driver for block replication, Wen Congyang, 2015/10/26
- Re: [Qemu-devel] [Qemu-block] [PATCH v10 08/10] Implement new driver for block replication, Stefan Hajnoczi, 2015/10/27
Re: [Qemu-devel] [Qemu-block] [PATCH v10 08/10] Implement new driver for block replication, Stefan Hajnoczi, 2015/10/15