Disable screen blanking on VT switch

[Connor Behan]

Dave Airlie wrote:
> On Sat, Jan 17, 2009 at 3:19 PM, Connor Behan<connor.behan at gmail.com>  wrote:
>    
>> I have two video cards each hooked up to a different monitor. The AGP
>> card driving my laptop screen is the boot display device which shows the
>> console and I've configred xorg to use the PCI card driving my external
>> monitor when I start it. I can use Ctrl+Alt+Fn to switch between X on
>> the big screen and a ttyn on the small screen but whenever I do so, the
>> inactive screen is not surprisingly blank. I'd like to be able to see X
>> persist on my external monitor when a text console is in the foreground
>> and eventually to see the output of a background tty on my laptop screen
>> when tty7 is in the foreground.
>>
>> I know the second direction sounds harder... people have been asking
>> questions about it since 2002 and the only solutions I've seen have been
>> unstable kernel patches that are now dead. But I am naive enough to
>> think that X could be configured to not blank the screen even when its
>> own console is switched away from. After all, it's still running. Do you
>> know of a way to do this? I've tried all combinations of tty and vt
>> related arguments to X but haven't got it to work yet.
>>
>> One thing that I think might work, is initializing a framebuffer for
>> both cards and then using con2fb to move a particular console to the
>> other framebuffer before starting X. I can't try this however because
>> all framebuffer drivers I've tried only create a framebuffer device for
>> the primary AGP card. So do you know how to disable screen blanking when
>> switching VTs or how to use multiple monitors with a framebuffer driver?
>> Thanks alot.
>>      
>
> X at least with normal drivers can't do this, there is only one VT and
> when X is switched
> all the screens it controls go away, you can't do text mode and X at
> the same time on multiiple cards
> with the current system AFAIK.
>
> fbdev might be an option but again I'm not sure, you'd need to avoid
> the VT switch in X, using
> (sharevts or novtswitch type options).
>
> Dave.
>    
Do you know what function makes all the screens go away when X is 
switched? I've tried to find out but this is probably way beyond my 
skill level. Is it in hw/xfree86/os-support/linux/lnx_init.c? Is one of 
the "restored permissions" in restoreVTPerms the fact that background 
consoles do not have permission to control screens? Or do the TRUE and 
FALSE return values in VTsw_noop.c and VTsw_usl.c somehow indicate that 
X should or shouldn't keep displaying on its screens? I can get 
VT-X1550PCI256 to display on my laptop screen while X is running. That's 
just the name of my card and when I switch Vts then switch back it goes 
away. But if X knows how to display that perhaps it could be made to 
display something else? Also a comment in lnx_init.c says "Detach from 
the controlling tty to avoid char loss"... by char loss does that mean 
loss of the characters that the textmode tty showed before X was 
started. And avoiding char loss means preventing that tty from going 
invisible?

I've also treid getting X to start in GNU screen so as to use screen 
keycodes to switch between multiplexed terminals instead of Ctrl+Alt+Fn 
to switch between ttys. Do you think this method is hopeless too?