VGA arbitration: API proposal

[Benjamin Herrenschmidt]

On Sat, 2005-03-05 at 18:37 +0000, Alan Cox wrote:
> On Sad, 2005-03-05 at 16:37, Jon Smirl wrote:
> > What about legacy code that doesn't contain vga_get/vga_put. brackets?
> > You can't just do this on VT switch in the simultaneous user case.
> 
> I don't think that bit is actually the problem.
> 
> Right now the console is kernel side so is easy and can do vga_get/put
> itself happily enough. The fun starts with the user space applications.
> Now all of these tell the kernel they are using the graphics directly
> via a vt ioctl that currently means "don't print panic messages, do
> funky vt switch". That ioctl can be made to mean "older user space
> application hogging the vga".
> 
> The bigger question is what the API for userspace looks like for new
> "well behaved" applications that touch on VGA because the moment a user
> app can lock vga we are in deadlock paradise. We may in fact need a
> kernel API on the vga device to "issue vga sequence to device" which
> does the locking entirely in kernel.

Do you think ? I had in mind something simpler, because there are only
very few apps that will have to bother, mostly X, and those are already
kernel crashing paradise anyway :)

I had in mind to base the API on some kind of file semantic (maybe
a /dev despite that beeing unfashionable lately) so that killing the app
will allow us to easily release it's "resource" (the VGA lock) when the
file gets closed.

Ben.