Re: [Qemu-devel] Connecting vde and LAN

["Jim C. Brown" <jma5@umd.edu>]

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On Mon, Jul 11, 2005 at 09:50:11AM +0200, Henrik Nordstrom wrote:
> On Sun, 10 Jul 2005, Jim C. Brown wrote:
> 
> I didn't mean to implement this in qemu directly, but rather in a helper 
> similar to vdeq, but the primary method should be via vde_switch. Having 
> this shortcut helper is a future extension.
> 

Ooooh! Like slirpvde.

> Inspired by this discussion I now have a prototype vde_packet glue for 
> vde_switch at http://www.henriknordstrom.net/examples/vde_packet.c, 
> connecting the vde_switch to the LAN via a packet socket.
> 

Excellent work! I've attached a modified version called vde_pcap.c, which
uses libpcap to do the dirty work instead. I haven't gotten all the linuxisms
out of it yet, but it should be easy to fix. One day, this might run on Windows
hosts.

> 
> b) can't talk to the host itself. This is due to the packets going 
> directly to the wire and never really "seen" by the host stack. Not sure 
> yet if there is an easy way out, but I suppose it may be possible to set 
> up a dummy tap with the same MAC and IP address as the base Ethernet 
> device and duplicate broadcasts and packet directed to the host there, 
> obviously assuming the administrator does not block this in firewalling..
> 
> Regards
> Henrik
> 

Alas, the accepted solution to allow pcap programs to talk to the host is to
use tuntap to create a tap device and connect the program to the tap device
instead of the real ethernet device.

-- 
Infinite complexity begets infinite beauty.
Infinite precision begets infinite perfection.

[-- Attachment #2: vde_pcap.c --]
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/* Copyright (C) 2005 Jim Brown
 * Copyright (C) 2005 Henrik Nordstrom
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111, USA.
 *
 * The VDE connection setup (open_vde) is loosely based on a similar
 * functions in vdeq.c by Renzo Davoli
 */

#include <sys/socket.h>
#include <netpacket/packet.h>
#include <net/ethernet.h>       /* the L2 protocols */
#include <sys/ioctl.h>
#include <fcntl.h>
#include <net/if.h>
#include <net/if_arp.h>
#include <sys/un.h>
#include <errno.h>

#include <linux/if_tun.h>

#include <stdio.h>
#include <string.h>
#include <stdint.h>
#include <stdlib.h>

#include <pcap.h>

#define SWITCH_MAGIC 0xfeedface
#define BUFSIZE 2048
#define ETH_ALEN 6
#define PCAP_READ_TIMEOUT 1

enum request_type {
    REQ_NEW_CONTROL
};

struct request_v3 {
    uint32_t magic;
    uint32_t version;
    enum request_type type;
    struct sockaddr_un sock;
};

static int
open_vde(char *name, int intno, int group)
{
    int pid = getpid();
    struct request_v3 req;
    int fdctl;
    int fddata;
    struct sockaddr_un sock;

    if ((fdctl = socket(AF_UNIX, SOCK_STREAM, 0)) < 0) {
	perror("socket");
	exit(1);
    }
    sock.sun_family = AF_UNIX;
    snprintf(sock.sun_path, sizeof(sock.sun_path), "%s", name);
    if (connect(fdctl, (struct sockaddr *) &sock, sizeof(sock))) {
	perror("connect");
	exit(1);
    }
    memset(&req, 0, sizeof(req));
    req.magic = SWITCH_MAGIC;
    req.version = 3;
    req.type = REQ_NEW_CONTROL + ((group > 0) ? ((geteuid() << 8) + group) << 8 : 0);
    req.sock.sun_family = AF_UNIX;
    sprintf(&req.sock.sun_path[1], "%5d-%2d", pid, intno);

    if ((fddata = socket(AF_UNIX, SOCK_DGRAM, 0)) < 0) {
	perror("socket");
	exit(1);
    }
    if (bind(fddata, (struct sockaddr *) &req.sock, sizeof(req.sock)) < 0) {
	perror("bind");
	exit(1);
    }
    if (send(fdctl, &req, sizeof(req), 0) < 0) {
	perror("send");
	exit(1);
    }
    if (recv(fdctl, &sock, sizeof(struct sockaddr_un), 0) < 0) {
	perror("recv");
	exit(1);
    }
    if (connect(fddata, (struct sockaddr *) &sock, sizeof(struct sockaddr_un)) < 0) {
	perror("connect");
	exit(1);
    }
    /* note: fdctl is intentionally leaked. Closed on exit by the OS. */
    return fddata;
}

void
set_nonblocking(int fd)
{
    int fl = fcntl(fd, F_GETFL);
    fcntl(fd, F_SETFL, (fl | O_NONBLOCK));
}

void
pcap_relay(u_char *args, const struct pcap_pkthdr *header, const u_char * packet)
{
    int * vde_socket = (int *)args;
    send(*vde_socket, packet, header->len, 0);
}

static void
wrap_dispatch(fd_set * rfd, pcap_t * handle, int vde_socket)
{
    int n;

    if (FD_ISSET(pcap_get_selectable_fd(handle), rfd)) {
	n = pcap_dispatch(handle, -1, pcap_relay, (u_char *)&vde_socket);
    }
}

int pcap_sendpacket(pcap_t * handle, const u_char * packet, int len)
{
   if (send(pcap_fileno(handle), packet, len, 0) == len)
   {
	return 0;
   }
   else
   {
	return -1;
   }
}

static void
relay(fd_set * rfd, int vde_socket, pcap_t * handle)
{
    int n;
    char packet[65536];
    union {
	struct sockaddr_ll ll;
	struct sockaddr_un un;
    } sa;
    socklen_t sa_len = sizeof(sa);

    if (FD_ISSET(vde_socket, rfd)) {
	n = recvfrom(vde_socket, packet, sizeof(packet), 0, (struct sockaddr *)&sa, &sa_len);
	if (n > 0)
	    pcap_sendpacket(handle, packet, n);
	else if (n == 0)
	    exit(1);
	else if (errno != EINTR) {
	    perror("recv:");
	    exit(1);
	}
    }
}

int
main(int argc, char **argv)
{
    int vde_socket;
    pcap_t * handle;
    char errbuf[PCAP_ERRBUF_SIZE];
    const u_char * packet;
    fd_set rfd;
    int fds;

    if (argc != 3) {
	printf("Usage: %s interface vde_socket\n", argv[0]);
	exit(1);
    }
    handle = pcap_open_live(argv[1], BUFSIZ, 1, PCAP_READ_TIMEOUT, errbuf);
    if (handle == NULL)
    {
    	printf("%s\n", errbuf);
	exit(1);
    }
    vde_socket = open_vde(argv[2], 0, 0);
    set_nonblocking(vde_socket);

    fds = pcap_get_selectable_fd(handle);
    if (vde_socket > fds)
	fds = vde_socket;
    fds += 1;
    FD_ZERO(&rfd);
    int i;
    for (;;) {
	int n;
	FD_SET(pcap_get_selectable_fd(handle), &rfd);
	FD_SET(vde_socket, &rfd);

	n = select(fds, &rfd, NULL, NULL, NULL);
	if (n > 0) {
	    wrap_dispatch(&rfd, handle, vde_socket);
	    relay(&rfd, vde_socket, handle);
	} else if (n < 0 && errno != EINTR) {
	    perror("select:");
	}
    }
}