Re: [Qemu-devel] [PULL 00/14] Net patches

[Jason Wang <jasowang@redhat.com>]

On 03/10/2016 11:51 AM, Li Zhijian wrote:
>
>
> On 03/10/2016 10:28 AM, Jason Wang wrote:
>>
>>
>> On 03/08/2016 05:54 PM, Peter Maydell wrote:
>>> On 8 March 2016 at 16:06, Zhang Chen <zhangchen.fnst@cn.fujitsu.com>
>>> wrote:
>>>> I found the reason for this problem is that
>>>> unix_connect() have not connect to sock_path before iov_send().
>>>> It need time to establish connection. so can we fix it with usleep()
>>>> like this:
>>>>
>>>>      recv_sock = unix_connect(sock_path, NULL);
>>>>      g_assert_cmpint(recv_sock, !=, -1);
>>>> +    usleep(1000);
>>>>
>>>>      ret = iov_send(send_sock[0], iov, 2, 0, sizeof(size) +
>>>> sizeof(send_buf));
>>>>      g_assert_cmpint(ret, ==, sizeof(send_buf) + sizeof(size));
>>>>      close(send_sock[0]);
>>>>
>>>>      ret = qemu_recv(recv_sock, &len, sizeof(len), 0);
>>> I would prefer it if we could find a way to fix this race
>>> reliably rather than just inserting a delay and hoping it
>>> is sufficient. Otherwise the test is likely to be unreliable
>>> if run on a heavily loaded or slow machine.
>>>
>>> thanks
>>> -- PMM
>>>
>>
>> +1
>>
>> To make sure the connected socket to be proceeded before iov_send(), you
>> could use some like  qmp("{ 'execute' : 'query-status'}") before
>> iov_send(). With this we are guaranteed that connected is setting to
>> true before iov_send().
>>
>>
>
> it seem works, but i don't know.
> Is this because that both qemu accepting the connection and qmp
> command are working under *iothread*,
> so that when the qemu command returns, we can guaranteed the
> connection is accepted ?

I think the problem is the race in main loop between the two handlers.
If the socket netdev read handler was proceed before chardev read
handler, since connected was false the packet will be dropped silently.
After we place whateve a qmp command in the middled, it's guaranteed
that all handlers were proceed after qmp command was executed, so we are
sure the connected is true when doing iov_send().

>
> Thanks
> Li Zhijian
>>
>>
>>
>
>
>