Re: [Qemu-devel] [PATCH] RFC: net/socket: learn to talk with a unix dgram socket

[Jason Wang <jasowang@redhat.com>]

On 2019/3/8 上午12:18, Marc-André Lureau wrote:
> Hi Jason
>
> On Thu, Nov 15, 2018 at 3:39 AM Jason Wang<jasowang@redhat.com>  wrote:
>> On 2018/11/14 下午9:01, Marc-André Lureau wrote:
>>> Hi
>>>
>>> On Wed, Nov 14, 2018 at 7:46 AM Jason Wang<jasowang@redhat.com>  wrote:
>>>> On 2018/11/10 上午3:56, Marc-André Lureau wrote:
>>>>> -net socket has a fd argument, and may be passed pre-opened sockets.
>>>>>
>>>>> TCP sockets use framing.
>>>>> UDP sockets have datagram boundaries.
>>>>>
>>>>> When given a unix dgram socket, it will be able to read from it, but
>>>>> will attempt to send on the dgram_dst, which is unset. The other end
>>>>> will not receive the data.
>>>>>
>>>>> Let's teach -net socket to recognize a UNIX DGRAM socket, and use the
>>>>> regular send() command (without dgram_dst).
>>>>>
>>>>> This makes running slirp out-of-process possible that
>>>>> way (python pseudo-code):
>>>>>
>>>>> a, b = socket.socketpair(socket.AF_UNIX, socket.SOCK_DGRAM)
>>>>>
>>>>> subprocess.Popen('qemu -net socket,fd=%d -net user' % a.fileno(), shell=True)
>>>>> subprocess.Popen('qemu ... -net nic -net socket,fd=%d' % b.fileno(), shell=True)
>>>>>
>>>>> (to make slirp a seperate project altogether, we would have to have
>>>>> some compatibility code and/or deprecate various options & HMP
>>>>> commands for dynamic port forwarding etc - but this looks like a
>>>>> reachable goal)
>>>>>
>>>>> Signed-off-by: Marc-André Lureau<marcandre.lureau@redhat.com>
>>>> I believe instead of supporting unnamed sockets, we should also support
>>>> named one through cli?
>>> This could be a later patch, I have no need for it yet. Perhaps it
>>> should be a chardev then?
>> I mean something like: -socket id=ud0,path=/tmp/XXX
>>
> Why not, but I have no need for it. If somebody has, he can make a patch.
>
>>>>> ---
>>>>>     net/socket.c | 25 +++++++++++++++++++++----
>>>>>     1 file changed, 21 insertions(+), 4 deletions(-)
>>>>>
>>>>> diff --git a/net/socket.c b/net/socket.c
>>>>> index 7095eb749f..8a9c30892d 100644
>>>>> --- a/net/socket.c
>>>>> +++ b/net/socket.c
>>>>> @@ -119,9 +119,13 @@ static ssize_t net_socket_receive_dgram(NetClientState *nc, const uint8_t *buf,
>>>>>         ssize_t ret;
>>>>>
>>>>>         do {
>>>>> -        ret = qemu_sendto(s->fd, buf, size, 0,
>>>>> -                          (struct sockaddr *)&s->dgram_dst,
>>>>> -                          sizeof(s->dgram_dst));
>>>>> +        if (s->dgram_dst.sin_family != AF_UNIX) {
>>>>> +            ret = qemu_sendto(s->fd, buf, size, 0,
>>>>> +                              (struct sockaddr *)&s->dgram_dst,
>>>>> +                              sizeof(s->dgram_dst));
>>>>> +        } else {
>>>>> +            ret = send(s->fd, buf, size, 0);
>>>>> +        }
>>>> Any reason that send is a must here? send(2) said:
>>>>           call
>>>>
>>>>               send(sockfd, buf, len, flags);
>>>>
>>>>           is equivalent to
>>>>
>>>>               sendto(sockfd, buf, len, flags, NULL, 0);
>>> Yes they should be equivalent, but then we need to add ?: operators
>>> for the dest arguments. I preferred to have an if() instead.
>>>
>>> thanks
>> One possible issue here is I'm not sure there's a equivalent send() in
>> e.g non POSIX system.
> send() should be as common as sendto().
>
> Should I resend the patch without RFC?


Yes please.


> no other changes needed?


No.

Thanks


>
> thanks!
>