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

[Alberto Garcia]

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