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

[Jason Wang]

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<address@hidden>  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<address@hidden>  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<address@hidden>
> > > > 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!