netdev - Re: Possible networking regression in 3.6.0

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Date:	Thu, 27 Sep 2012 23:03:46 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Chris Clayton <chris2553@...glemail.com>
Cc:	netdev@...r.kernel.org, gpiez@....de
Subject: Re: Possible networking regression in 3.6.0

On Thu, 2012-09-27 at 19:05 +0100, Chris Clayton wrote:
> On 09/27/12 13:14, Eric Dumazet wrote:
> > On Thu, 2012-09-27 at 12:50 +0100, Chris Clayton wrote:
> >> Just for information - I've pulled Linus' tree this morning and the
> >> problem is still present. Also, Gunther Piaz has reported, via the
> >> bugzilla entry, that he too has hit this regression.
> >
> > I tried to reproduce the bug, and my kvm guests have no problem.
> >
> > I guess you need to precisely describe how you setup your network, so
> > that I can reproduce the problem and eventually fix it.
> >
> 
> You've seen the bits from my firewall setup script that relate to this 
> issue. I start the WinXP client with another script:
> 
> #!/bin/sh
> if [ -e $HOME/kvm/var/run/kvm-winxp.pid ]; then
>      echo "winxp is already running ..." > /dev/stderr
>      exit 1
> fi
> 
> # make sure the kvm modules are loaded
> if test -z "$(grep '\<kvm\>' /proc/misc)"; then
>      sudo modprobe kvm-intel
>      while test -z "$(grep '\<kvm\>' /proc/misc)"; do
>          true
>      done
> fi
> 
> # make sure tun module is loaded
> if test ! -e /dev/net/tun; then
>      sudo modprobe tun
> fi
> 
> # figure out the cpu to use
> QVER=$(qemu-kvm --version | cut -d' ' -f 4 | sed 's/,/./')
> # assumes major version is 1
> MINORVER=$(echo $QVER | cut -d'.' -f 2)
> if [ $MINORVER -ge 1 ]; then
>      CPU="host"
> else
>      CPU="qemu64"
> fi
> 
> # set up the network interface
> TAPDEV=$(sudo tunctl -b -u $(whoami))
> sudo ifconfig $TAPDEV 192.168.200.254 netmask 255.255.255.0 broadcast 
> 192.168.200.255
> 
> # start Windows XP
> qemu-kvm -drive file=$HOME/kvm/winxp.qcow2,index=0,cache=none,if=virtio 
> -cpu $CPU -smp cores=1,threads=2 -soundhw es1370 \
>      -m 768 -net nic,model=virtio,macaddr=$(getmacaddr) -net 
> tap,ifname=$TAPDEV -startdate $(date +%Y-%m-%dT%H:%M:%S) \
>      -name kxplaptop -pidfile $HOME/kvm/var/run/kvm-winxp.pid $*
> 
> # stop the network interface
> sudo ifconfig $TAPDEV down
> sudo tunctl -d $TAPDEV &>/dev/null
> 
> # tidy up
> rm -f $HOME/kvm/var/run/kvm-winxp.pid
> 
> 
> The call to getmacaddr just returns the next in a sequence of mac 
> addresses. qemu-kvm is a symlink to /usr/bin/qemu-system-i386. I first 
> found the problem whilst running qemu-kvm version 1.1.1 although I've 
> since updated to 1.2.0.
> 
> By the way, I doubt it will make a difference, but, although my laptop 
> has a 64bit CPU, I am running a 32 bit kernel and, obviously, user space.
> 
> Let me know if you need anything else.

It works for me.

Hmm, maybe your guest is using DHCP and DHCP fails ?

Could you check ?



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