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

["Sebastian Herbszt" <herbszt@gmx.de>]

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.

>> 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.

>> +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

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

Otherwise it seems to compile and run fine.

- Sebastian