Re: [Qemu-block] [PATCH v3 18/19] nbd/client: Work around 3.0 bug for listing meta contexts

[Vladimir Sementsov-Ogievskiy]

17.01.2019 6:21, Eric Blake wrote:
> On 1/16/19 9:43 AM, Vladimir Sementsov-Ogievskiy wrote:
> 
>>> @@ -839,9 +842,25 @@ static int nbd_list_meta_contexts(QIOChannel *ioc,
>>>
>>>            ret = nbd_receive_one_meta_context(ioc, 
>>> NBD_OPT_LIST_META_CONTEXT,
>>>                                               &context, NULL, errp);
>>> +        if (ret == 0 && seen_any && !seen_qemu) {
>>> +            /*
>>> +             * Work around qemu 3.0 bug: the server forgot to send
>>> +             * "qemu:" replies to 0 queries. If we saw at least one
>>> +             * reply (probably base:allocation), but none of them were
>>
>> if we are saying about 3.0, it is base:allocation for sure, isn't it?
>>
>>> +             * qemu:, then run a more specific query to make sure.
> 
> If the server is qemu 3.0, then yes, it is base:allocation. But it could
> be some other server that has its own custom return without implementing
> base:allocation.

Indeed) And in this context, heuristic about that server should have at least 
one
context listed with no query seems not generic. Why not query 'qemu:' even if 
empty
query returns nothing? So, at least, "probably" is imbalanced with this not 
described
in comment heuristic which seems bound to 3.0.

> 


-- 
Best regards,
Vladimir