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net/socket: learn to talk with a unix dgram socket

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-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)

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>
This commit is contained in:
Marc-André Lureau 2019-03-11 18:25:05 +01:00 committed by Jason Wang
parent a04d91c701
commit fdec16e3c2
1 changed files with 21 additions and 4 deletions
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25
net/socket.c
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@ -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);
}
} while (ret == -1 && errno == EINTR);
if (ret == -1 && errno == EAGAIN) {
@ -336,6 +340,15 @@ static NetSocketState *net_socket_fd_init_dgram(NetClientState *peer,
int newfd;
NetClientState *nc;
NetSocketState *s;
SocketAddress *sa;
SocketAddressType sa_type;
sa = socket_local_address(fd, errp);
if (!sa) {
return NULL;
}
sa_type = sa->type;
qapi_free_SocketAddress(sa);
/* fd passed: multicast: "learn" dgram_dst address from bound address and save it
* Because this may be "shared" socket from a "master" process, datagrams would be recv()
@ -379,8 +392,12 @@ static NetSocketState *net_socket_fd_init_dgram(NetClientState *peer,
"socket: fd=%d (cloned mcast=%s:%d)",
fd, inet_ntoa(saddr.sin_addr), ntohs(saddr.sin_port));
} else {
if (sa_type == SOCKET_ADDRESS_TYPE_UNIX) {
s->dgram_dst.sin_family = AF_UNIX;
}
snprintf(nc->info_str, sizeof(nc->info_str),
"socket: fd=%d", fd);
"socket: fd=%d %s", fd, SocketAddressType_str(sa_type));
}
return s;