Re: [Xen-devel] [PATCH] Paravirt framebuffer console cleanups [5/5]

[Steven Smith <sos22-xen@xxxxxxxxxxxxx>]

> On Mon, 2006-09-04 at 10:02 +0100, Steven Smith wrote:
> > > diff -r c859588adc5e -r 72582b968445 
> > > linux-2.6-xen-sparse/drivers/char/tty_io.c
> > > --- a/linux-2.6-xen-sparse/drivers/char/tty_io.c  Sat Sep 02 15:31:29 
> > > 2006 -0400
> > > +++ b/linux-2.6-xen-sparse/drivers/char/tty_io.c  Sat Sep 02 15:32:38 
> > > 2006 -0400
> > 
> > It looks to me like this patch makes tty_io.c identical to the
> > upstream version.  Is this correct?
> Yep -- so actually could be removed from the sparse tree.  I'm usually
> working in a non-sparse tree, so the diff is more relevant.
Ack.

> > > diff -r c859588adc5e -r 72582b968445 
> > > linux-2.6-xen-sparse/drivers/xen/console/console.c
> > > --- a/linux-2.6-xen-sparse/drivers/xen/console/console.c  Sat Sep 02 
> > > 15:31:29 2006 -0400
> > > +++ b/linux-2.6-xen-sparse/drivers/xen/console/console.c  Sat Sep 02 
> > > 15:32:38 2006 -0400
> > > @@ -663,6 +663,20 @@ static int __init xencons_init(void)
> > >   printk("Xen virtual console successfully installed as %s%d\n",
> > >          DRV(xencons_driver)->name, xc_num);
> > >  
> > > +        /* Don't need to check about graphical fb for domain 0 */
> > > +        if (is_initial_xendomain())
> > > +   return 0;
> > > +
> > > + rc = 0;
> > > + if (xenbus_scanf(XBT_NIL, "console", "use_graphics", "%d", &rc) < 0)
> > > +         printk(KERN_ERR "Unable to read console/use_graphics\n");
> > > + if (rc == 0) {
> > > +               /* FIXME: this is ugly */
> > > +        unregister_console(&kcons_info);
> > > +        kcons_info.flags |= CON_CONSDEV;
> > > +        register_console(&kcons_info);
> > > + }
> > > +
> > Could you pull the setting of CON_CONSDEV into xen_console_init and
> > avoid this weirdness?
> Nope -- when consoles are registered, we don't have enough
> infrastructure to check xenbus to see if console/use_graphics is set or
> not
That's a pity.

> > This whole passage is a little peculiar, in that you're only going to
> > do anything if use_graphics is disabled.  I'd expect that just leaving
> > the current behaviour alone would be the correct thing to do in that
> > case.
> > 
> > Also, why do you need to set CON_CONSDEV at all?
> 
> Otherwise, you don't get kernel console messages.
Why not?  None of the other console drivers seem to need to set it
explicitly, and it seems like it would break setting console=blah on
the kernel command line.

It also strikes me as very odd that you need to do this iff
use_graphics is switched off.

> Realistically, I think the better longer-term answer is to create an
> early xenconsole -- then, when we do this later initialization, we can
> deregister the early console and do the right registration for the
> "real" console.  This mirrors pretty closely what's done on a few other
> arches
Agreed, but not in this patch series.

Steven.

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