[Qemu-devel] Re: [PATCH] networking using libpcap

[Jung-uk Kim <jkim@FreeBSD.org>]

On Friday 18 July 2008 12:12 pm, Sebastian Herbszt wrote:
> Jung-uk Kim wrote:
> > Since someone showed interest, I updated my patches against
> > trunk. :-)
> >
> > http://people.freebsd.org/~jkim/qemu-pcap-20080717.diff
> >
> > I turned it off by default for now.  If you want to enable it,
> > do:
> >
> > configure --enable-pcap
>
> To avoid confusion please change the pcap probe to error instead of
> silently setting pcap=no. Take a look at audio_drv_probe.

Done.

> >> Works perfect for me and allows access to the local Ethernet
> >> right out of the box, very much unlike tap and bridging. The
> >> attached version applies to trunk.
> >>
> >> I have modified (e.g. got rid of threads) the original patch
> >> from the forum and am using it here on Windows. It works fine
> >> but performance is pretty low.
> >
> > *After* applying the new patch:
> >
> > cp -p vl.c vl.c.orig
> > sed -e 's/#ifdef PCAP_SET_FILTER/#if 1/g' vl.c > vl.c.tmp
> > mv vl.c.tmp vl.c
> >
> > and try again?  BTW, I have no real experience with WinPcap, so
> > don't kill me if it does not work for you. ;-)
>
> Using pcap_setfilter helps and colinux (conet-bridged-daemon) does
> use one too. Currently your filter is
> "ether dst 52:54:00:12:34:56 or ((broadcast or multicast) and not
> ether src 52:54:00:12:34:56)". The filter used by colinux is
> "(ether dst 00:ff:81:24:00:00) or (ether broadcast or multicast) or
> (ip broadcast or multicast)".
>
> The "and not ether src 52:54:00:12:34:56" part in your filter
> prevents the VM from seeing own packets. It doesn't reply to own
> "ping broadcast" where it does in colinux and VMware Server.

I knew that I might have missed some edge cases. ;-P Corrected and 
enabled by default.

> >> +ifdef CONFIG_PCAP
> >> +LIBS+=-lpcap
> >> +endif
> >>
> >> On Windows it should be -lwpcap.
> >
> > Thanks for the tip!
> >
> >> +    if ((fd = pcap_get_selectable_fd(s->handle)) < 0) {
> >> + fprintf(stderr, "qemu: pcap_get_selectable_fd failed\n");
> >> + goto fail;
> >> +    }
> >> +    qemu_set_fd_handler(fd, pcap_send, NULL, s);
> >>
> >> pcap_get_selectable_fd() is not available on Windows. I just put
> >> pcap_send() in main_loop_wait().
> >
> > I added WinPcap API support from WinPcap manual pages but I have
> > no way of checking.  Can you try the patch and letting me know?
>
> Since you use the winpcap win32 only parts there is the following
> warning:
>
> vl.c: In function `net_pcap_init':
> vl.c:4247: warning: implicit declaration of function
> `pcap_getevent' vl.c:4247: warning: assignment makes pointer from
> integer without a cast
>
> You can avoid it by defining WPCAP in vl.c:
>
> #if defined(CONFIG_PCAP)
> #ifdef _WIN32
> #define WPCAP 1
> #endif
> #include <pcap.h>
> #endif

Thanks for the tip, again!

> I noticed that if no ifname is passed you try to get one with
> pcap_lookupdev. This is broken on winpcap, please see
> http://www.winpcap.org/pipermail/winpcap-bugs/2006-May/000220.html

I don't think it is "broken" on Windows.  The OP was just saying that 
it returns device name in wide characters on Windows.  In fact, both 
tcpdump (3.9.8) and WinDump (3.9.5) seem to do the same (trimmed 
formatting):

-----------------
	if (device == NULL) {
		device = pcap_lookupdev(ebuf);
			if (device == NULL)
				error("%s", ebuf);
	}
#ifdef WIN32
	//we assume that an ASCII string is always longer than 1 char
	if(strlen(device) == 1)
	{	//a Unicode string has a \0 as second byte (so strlen() is 1)
		fprintf(stderr, "%s: listening on %ws\n", program_name, device);
	}
	else
	{
		fprintf(stderr, "%s: listening on %s\n", program_name, device);
	}

	fflush(stderr);
#endif /* WIN32 */
	*ebuf = '\0';
	pd = pcap_open_live(device, snaplen, !pflag, 1000, ebuf);
	if (pd == NULL)
		error("%s", ebuf);
	else if (*ebuf)
		warning("%s", ebuf);
-----------------

The OP had to use %ws format, not just %s, it seems.  In fact, WinPcap 
seems to convert ASCII names to Unicode names unconditionally from 
pcap_lookupdev():

	/*
	 * Windows NT (NT 4.0, W2K, WXP). Convert the names to UNICODE for 
backward compatibility
	 */

> I am not sure if pcap_lookupdev() gets you the "right" interface on
> non-win32, so maybe just require ifname (tap does it too)?

At least, it works for me on FreeBSD. :-) Does WinDump work without 
specifying interface name when there is only one network device?  If 
it does, I am not going to change it.

> Otherwise it seems to compile and run fine.

Please try the updated patch and let me know:

http://people.freebsd.org/~jkim/qemu-pcap-20080718.diff

Note I had to re-shuffle the patch a bit to make it applicable to 
slightly older sources.

Juergen,

I simplified FreeBSD ports patch with the above patch:

http://people.freebsd.org/~jkim/qemu-devel-20080620_1-pcap.diff

Thanks!

Jung-uk Kim