Re: Console unregistration questions

[Jesse Barnes <jbarnes@virtuousgeek.org>]

On Tuesday, April 24, 2007, Antonino A. Daplas wrote:
> > But since we're using drmfb as a console, the unregister_framebuffer
> > call silently fails.  fbcon is builtin to the kernel, so when drmfb
> > exits, unregister_framebuffer will end up calling fbcon's
> > fbcon_fb_unregistered() function via the notifier chain.  However,
> > when fbcon_fb_unregistered calls unregister_con_driver(&fb_con) it
> > ignores the return value, which is bad since unregister_con_driver
> > left fbcon's routines active (due to fbcon still being bound to the
> > console) even while unregister_framebuffer freed their underlying
> > structures.
>
> Okay, we can do that. This was not done before because
> unregister_framebuffer was only called on rmmod <module>.  But checking
> for the return error and have it propagate to the driver should not be a
> problem.
>
> I'll send a patch to you and to akpm soon.

Great!  Thanks.

> >   So when unregister_framebuffer returns, the
> > very next console operation causes an oops or worse (I usually see
> > hide_cursor->fbcon_cursor die when it tries to get at
> > info->fbcon_par).
> >
> > However, it doesn't appear that there's a way for fb drivers to unbind
> > themselves from the console at unload time, so we have to do it
> > manually.
>
> You cannot unbind framebuffer drivers independently from the console
> layer because the console is holding a reference count on them.
>
> FYI: this was what I did initially, but akpm objected :-).
>
> > Should there be a way to unbind it from driver code?  Maybe by
> > exporting a wrapper to unbind_con_driver?
>
> Yes, you can expose unbind_con_driver(), I don't mind. You can do it
> first in your tree, then when you need it for mainline, let me know.

So using unbind_con_driver is ok since we go through the console layer and 
all the refcounting is kosher?  The only other thing with 
unbind_con_driver is I'm not sure about the other arguments (first, last, 
& default) should be if called from a driver context.

Thanks,
Jesse



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