[PATCH v3] dix: adds support for none root window background

[Mark Kettenis]

> Date: Thu, 4 Nov 2010 17:40:55 +0200
> From: Pauli Nieminen <ext-pauli.nieminen at nokia.com>
> 
> On 03/11/10 22:17 +0100, Vignatti Tiago (Nokia-MS/Helsinki) wrote:
> > It lets the driver notify the server whether it can draw a background when
> > '-background none' option is used by the system platform. Use cases for that
> > could be video drivers performing mode-setting in kernel time, before X is up,
> > so a seamless transition would happen until X clients start to show up.
> > 
> > If the driver can copy the framebuffer cleanly then it can set the flag
> > (canDoBGNoneRoot), otherwise the server will fallback to the normal behaviour.
> > The system must explicit indicates willingness of doing so through
> > '-background none'. We could do this option as default; in such case,
> > malicious users would be able to steal the framebuffer with a bit of tricks.
> > 
> > For instance, I can see the content of my nVidia Quadro FX 580 framebuffer
> > old X session modifying a bit nv driver:
> > 
> > --- a/src/g80_driver.c
> > +++ b/src/g80_driver.c
> > @@ -850,17 +850,6 @@ G80ScreenInit(int scrnIndex, ScreenPtr pScreen, int argc,
> > c
> > 
> >      xf86DPMSInit(pScreen, xf86DPMSSet, 0);
> > 
> > -    /* Clear the screen */
> > -    if(pNv->xaa) {
> > -        /* Use the acceleration engine */
> > -        pNv->xaa->SetupForSolidFill(pScrn, 0, GXcopy, ~0);
> > -        pNv->xaa->SubsequentSolidFillRect(pScrn,
> > -            0, 0, pScrn->displayWidth, pNv->offscreenHeight);
> > -        G80DmaKickoff(pNv);
> > -    } else {
> > -        /* Use a slow software clear path */
> > -        memset(pNv->mem, 0, pitch * pNv->offscreenHeight);
> > -    }
> > +    pScreen->canDoBGNoneRoot = TRUE;
> > 
> > The commit is originally based on discussions happened on xorg-devel:
> > http://lists.freedesktop.org/archives/xorg-devel/2010-June/009755.html
> > 
> > Signed-off-by: Tiago Vignatti <tiago.vignatti at nokia.com>
> > ---
> 
> This patch looks good to me. But I don't know code well so only
> Acked-by: Pauli Nieminen <ext-pauli.nieminen at nokia.com>

Uh, do you really want to make the nv driver show whatever crap is in
the framebuffer when X starts up?