Re: pvops netconsole

[Jeremy Fitzhardinge <jeremy@goop.org>]

On 02/13/2010 06:28 PM, Brad Plant wrote:
> On Fri, 12 Feb 2010 15:09:12 -0800
> Jeremy Fitzhardinge<jeremy@goop.org>  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
>