Re: [Qemu-devel] [PATCH 2/2] block-stream: include base into job node list

[Andrey Shinkevich]

On 26/02/2019 16:33, Alberto Garcia wrote:
> On Mon 25 Feb 2019 05:39:14 PM CET, Vladimir Sementsov-Ogievskiy wrote:
>>> --- a/block/stream.c
>>> +++ b/block/stream.c
>>> @@ -259,6 +259,15 @@ void stream_start(const char *job_id, BlockDriverState 
>>> *bs,
>>>                               &error_abort);
>>>        }
>>>    
>>> +    if (base) {
>>> +        /*
>>> +         * The base node should not disappear during the job.
>>> +         */
>>> +        block_job_add_bdrv(&s->common, "base", base, 0,
>>> +                           BLK_PERM_ALL & ~BLK_PERM_GRAPH_MOD,
>>> +                           &error_abort);
>>> +    }
>>> +
>>>        s->base = base;
>>>        s->backing_file_str = g_strdup(backing_file_str);
>>>        s->bs_read_only = bs_read_only;
>>>
>>
>>
>> Hmm, intersting, is BLK_PERM_GRAPH_MOD a good way to lock relations in
>> node graph?
>>
>> bdrv_replace_node don't check this permission. So, I don't understand,
>> how this permission works.. Graph modification operation in difference
>> with read or write are not done through BdrvChild at all.
>>
>> Are there any ideas or work started for some another mechanism of
>> "freezing" a subgraph during an operation?
> 
> See this discussion:
> 
>     https://lists.gnu.org/archive/html/qemu-block/2018-11/msg00387.html
> 
> And these patches (currently under review):
> 
>     https://lists.gnu.org/archive/html/qemu-block/2019-01/msg00622.html
> 
> Berto
> 

The bdrv_freeze_backing_chain() excludes the base BlockDriverState.
And we would like to protect the base as well when running the
block-stream.
-- 
With the best regards,
Andrey Shinkevich