Re: [Qemu-devel] [PATCH 4/4] block/nbd-client: use non-blocking io channel for nbd negotiation

[Vladimir Sementsov-Ogievskiy]

12.02.2019 1:02, Eric Blake wrote:
> On 2/11/19 6:56 AM, Vladimir Sementsov-Ogievskiy wrote:
>> Now negotiation is done in coroutine, so to take benefit of it let's
>> use non-blocking model.
>>
>> Note that QIOChannel handle synchronous io calls correctly anyway, so
> 
> s/handle/handles/
> 
>> it's not a problem to send final NBD_CMD_DISC to non-blocking channel
>> but using sync qio interface, even not in coroutine.
> 
> s/not in/when not in a/
> 
>>
>> Signed-off-by: Vladimir Sementsov-Ogievskiy <address@hidden>
>> ---
>>   block/nbd-client.c | 10 +++-------
>>   1 file changed, 3 insertions(+), 7 deletions(-)
> 
> This fixes qemu as NBD client for use in block devices, but what about
> qemu as NBD client in qemu-nbd?  Does that need any updates?  Then
> again, your observation about QIO doing the right thing for both
> blocking (qemu-nbd) and non-blocking (block layer) channels seems to
> cover that.

In qemu-nbd client works in a separate thread, so, I think, we don't need
nonblocking: we have a thread anyway.

On the other hand, is my code in nbd_reaceive_common safe, keeping in mind
that we call it from separate thread?

Are qio_channel_attach_aio_context, qemu_aio_coroutine_enter, AIO_WAIT_WHILE
thread-safe?

> 
>> @@ -1072,9 +1072,6 @@ static int nbd_client_connect(BlockDriverState *bs,
>>           object_ref(OBJECT(client->ioc));
>>       }
>>   
>> -    /* Now that we're connected, set the socket to be non-blocking and
>> -     * kick the reply mechanism.  */
>> -    qio_channel_set_blocking(QIO_CHANNEL(sioc), false, NULL);
>>       client->connection_co = qemu_coroutine_create(nbd_connection_entry, 
>> client);
>>       nbd_client_attach_aio_context(bs, bdrv_get_aio_context(bs));
>>   
>> @@ -1083,9 +1080,8 @@ static int nbd_client_connect(BlockDriverState *bs,
>>   
>>    fail:
>>       /*
>> -     * We have connected, but must fail for other reasons. The
>> -     * connection is still blocking; send NBD_CMD_DISC as a courtesy
>> -     * to the server.
>> +     * We have connected, but must fail for other reasons.
>> +     * Send NBD_CMD_DISC as a courtesy to the server.
>>        */
>>       {
>>           NBDRequest request = { .type = NBD_CMD_DISC };
>>
> 


-- 
Best regards,
Vladimir