Re: [Qemu-devel] qemu tun networking bug

[Vitaly Belostotsky]

Thank you very much, Henrik,

based on your reply I've found the relevant linux kernel TUN/TAP problem 
description
in http://www.kernel.org/pub/linux/kernel/v2.6/testing/ChangeLog-2.6.11-rc2
and was able to workaround the problem in my case with the small patch:

--- qemu-0.7.0/vl.c.orig        2005-04-28 00:52:05.000000000 +0400
+++ qemu-0.7.0/vl.c     2005-07-12 13:14:11.583204352 +0400
@@ -1622,7 +1622,7 @@
         return -1;
     }
     memset(&ifr, 0, sizeof(ifr));
-    ifr.ifr_flags = IFF_TAP | IFF_NO_PI;
+    ifr.ifr_flags = IFF_TAP | IFF_NO_PI | IFF_ONE_QUEUE;
     pstrcpy(ifr.ifr_name, IFNAMSIZ, "tun%d");
     ret = ioctl(fd, TUNSETIFF, (void *) &ifr);
     if (ret != 0) {

May be the problem deserves mentioning in some qemu docs?

Regards
Vitaly

On Tue, Jul 12, 2005 at 03:09:43AM +0200, Henrik Nordstrom wrote:
> On Tue, 12 Jul 2005, Vitaly Belostotsky wrote:
> 
> >I've encountered some network related bug when using qemu with tun
> >and I'm willing to debug it but could you please provide some help.
> 
> you may want to try upgrading to the host kernel to 2.6.12. Had quite a 
> bit of issues with tun devices "hanging" in earlier Linux-2.6 versions, 
> but after I switched to a Fedora Core 4 host running Linux-2.6.12 things 
> seems much more stable.
> 
> My diagnostics at the time indicated some flow control problem within the 
> host kernle tun driver, making the driver stall and not deliver packets to 
> the application (qemu). Your findings seems to indicate very similar 
> result.
> 
> Regards
> Henrik
> 
> 
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