On 1/17/19 2:07 AM, Vladimir Sementsov-Ogievskiy wrote:
> 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?Because it is highly unlikely that we will ever encounter a server that knows how to serve "qemu:" contexts but not "base:allocation" (qemu is not such a server, and why would any other server bother with qemu: specific information?). > So, at least, "probably" is imbalanced with this not described > in comment heuristic which seems bound to 3.0. qemu 3.0 is the only server where the heuristic will make a difference, but not the only server where the heuristic may trigger. -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3226 Virtualization: qemu.org | libvirt.org
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