[Bug 638955] Re: [Qemu-devel] [PATCH] e1000: Pad short frames to minimum size (60 bytes)

[Edgar E. Iglesias]

On Mon, Sep 20, 2010 at 03:31:32PM -0500, Anthony Liguori wrote:
> On 09/20/2010 05:42 AM, Michael S. Tsirkin wrote:
> > On Sun, Sep 19, 2010 at 07:36:51AM +0100, Stefan Hajnoczi wrote:
> >    
> >> On Sat, Sep 18, 2010 at 10:27 PM, Edgar E. Iglesias
> >> <address@hidden>  wrote:
> >>      
> >>> This doesn't look right. AFAIK, MAC's dont pad on receive.
> >>>        
> >> I agree.  NICs that do padding will do it on transmit, not receive.
> >> Anything coming in on the wire should already have the minimum length.
> >>      
> > QEMU never gets access to the wire.
> > Our APIs do not really pass complete ethernet packets:
> > we forward packets without checksum and padding.
> >
> > I think it makes complete sense to keep this and
> > handle padding in devices because we
> > have devices that pass the frame to guest without padding and checksum.
> > It should be easy to replace padding code in devices that
> > need it with some kind of macro.
> >    
> 
> Would this not also address the problem?  It sounds like the root cause 
> is the tap code, not the devices..
> 
> Regards,
> 
> Anthony Liguori
> 
> >    
> >> In QEMU that isn't true today and that's why rtl8139, pcnet, and
> >> ne2000 already do this same padding.  This patch is the smallest
> >> change to cover e1000.
> >>
> >>      
> >>> IMO this kind of padding should somehow be done by the bridge that 
> >>> forwards
> >>> packets into the qemu vlan (e.g slirp or the generic tap bridge).
> >>>        
> >> That should work and we can then drop the padding code from existing
> >> NICs.  I'll take a look.
> >>
> >> Stefan
> >>      
> >    
> 

> From f77c3143f3fbefdfa2f0cc873c2665b5aa78e8c9 Mon Sep 17 00:00:00 2001
> From: Anthony Liguori <address@hidden>
> Date: Mon, 20 Sep 2010 15:29:31 -0500
> Subject: [PATCH] tap: make sure packets are at least 40 bytes long
> 
> This is required by ethernet drivers but not enforced in the Linux tap code so
> we need to fix it up ourselves.
> 
> Signed-off-by: Anthony Liguori <address@hidden>
> 
> diff --git a/net/tap.c b/net/tap.c
> index 4afb314..822241a 100644
> --- a/net/tap.c
> +++ b/net/tap.c
> @@ -179,7 +179,13 @@ static int tap_can_send(void *opaque)
>  #ifndef __sun__
>  ssize_t tap_read_packet(int tapfd, uint8_t *buf, int maxlen)
>  {
> -    return read(tapfd, buf, maxlen);
> +    ssize_t len;
> +
> +    len = read(tapfd, buf, maxlen);
> +    if (len > 0) {
> +        len = MAX(MIN(maxlen, 40), len);


A small detail :)
40 -> 64 (including a dummy FCS).


> +    }
> +    return len;
>  }
>  #endif
>  
> -- 
> 1.7.0.4
>

-- 
emulated netcards don't work with recent sunos kernel
https://bugs.launchpad.net/bugs/638955
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Status in QEMU: New

Bug description:
hi there,

i'm using qemu-kvm backend in version: # qemu-kvm -version
QEMU PC emulator version 0.12.5 (qemu-kvm-0.12.5), Copyright (c) 2003-2008 
Fabrice Bellard

and there are just *not working any of model=$type with combinations of recent 
sunos (solaris, openindiana, opensolaris, ..) ..

you can download for testing purposes iso from here: 
http://dlc-origin.openindiana.org/isos/147/ or from here: 
http://genunix.org/distributions/indiana/ << osol and oi are also bubuntu-like 
*live cds, so no need to bother with installing

behaviour is as follows:
e1000 - receiving doesn't work, transmitting works .. dladm (tool for handle 
ethers) shows that is all ok, correct mode is loaded up, it just seems like 
this driver works at 100% but ..

rtl8169|pcnet - works in 10Mbit mode with several other issues like high cpu 
utilization and so .. dladm is unable to recognize options for this kind of -nic

others - just don't work

.. i experienced this issue several times in past .. woraround was, that 
rtl8169 worked so-so .. with recent sunos kernel it doesn't.

it's easy to reproduce, this is why i'm not putting here more then launching 
script for my virtual machine:

# cat openindiana.sh
qemu-kvm -hda /home/kvm/openindiana/openindiana.img -m 2048 -localtime -cdrom 
/home/kvm/+images/oi-dev-147-x86.iso -boot d \
-vga std -vnc :9 -k en-us -monitor 
unix:/home/kvm/openindiana/instance,server,nowait \
-net nic,model=e1000,vlan=1 -net tap,ifname=oi0,script=no,vlan=1 &

sleep 2;
ip l set oi0 up;
ip a a 192.168.99.9/24 dev oi0;

regards by daniel