Re: [Xen-devel] pvops netconsole

[Jeremy Fitzhardinge <jeremy@xxxxxxxx>]

On 02/13/2010 06:28 PM, Brad Plant wrote:
> On Fri, 12 Feb 2010 15:09:12 -0800
> Jeremy Fitzhardinge<jeremy@xxxxxxxx>  wrote:
>
>    
> > On 02/04/2010 04:15 PM, Brad Plant wrote:
> >      
> > > Initialising Xen virtual ethernet driver.
> > > blkfront: xvda1: barriers enabled
> > > netconsole: local port 11111
> > > netconsole: local IP 10.20.40.2
> > > netconsole: interface eth1
> > > netconsole: remote port 9514
> > > netconsole: remote IP 10.20.50.2
> > > netconsole: remote ethernet address 00:16:3e:00:50:02
> > > netconsole: eth1 doesn't support polling, aborting.
> > > netconsole: cleaning up
> > >
> > >        
> > The xen-netfront device doesn't support the polling interface that
> > netconsole relies on.  It probably wouldn't be too hard to add that
> > capability if you want to.  It's independent of the backend and/or the
> > actual underlying hardware device.
> >      
> Ok, I've come up with something that "works". Patch against 2.6.32.7 is attached. While 
> it works, I've got no idea if what I've done is the "right way". I used virtio_net.c as a 
> guide.
>
> I've got some issues that I'm stuck on and would like some guidance:
>
> 1. When the first message is sent over the net console, the WARN_ONCE() at 
> net/core/netpoll.c:327 triggers. I'm not sure what to do about this.
>
>    
What's the backtrace in the warning?

I had a quick look at e1000's and it calls the interrupt handler; the 
netfront equivalent would be to call xennet_interrupt() with interrupts 
disabled.  I'm not sure virtio_net is a good model because it doesn't 
seem to have any interrupt-related stuff in it; I guess that happens 
elsewhere in virtio.
> 2. When either netconsole is setup or the first message is sent, messages 
> already logged to the main console get logged again. Maybe this will go away 
> when the above is fixed?
>    
Probably not.  It sounds like a feature.

> 3. Initially netconsole would not initialise because the interface didn't yet have a 
> mac address as setup_netfront hadn't yet been called. I changed the module_init() in 
> netconsole.c to late_initcall() if !CONFIG_MODULES&&  CONFIG_XEN. Is this 
> allowed and sane?
>    
Probably not.  In practice every kernel will have modules and Xen 
enabled, and it will change netconsole for all users.  I guess we 
probably need to find some way to init the MAC address earlier, or 
trigger netconsole init once the mac address is known.
> Cheers,
>
> Brad
>    

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