[PATCH 4/4] drm: Add getfb2 ioctl

[Ville Syrjälä]

On Fri, Mar 23, 2018 at 05:00:11PM +0000, Daniel Stone wrote:
> Hi,
> 
> On 23 March 2018 at 14:49, Ville Syrjälä <ville.syrjala at linux.intel.com> wrote:
> > On Fri, Mar 23, 2018 at 01:45:52PM +0000, Daniel Stone wrote:
> >> +     for (i = 0; i < ARRAY_SIZE(r->handles); i++) {
> >> +             r->handles[i] = 0;
> >> +             r->pitches[i] = 0;
> >> +             r->offsets[i] = 0;
> >> +             r->modifier[i] = DRM_FORMAT_MOD_INVALID;
> >
> > Don't we want to leave this zeroed too? For addfb2 we require any unused
> > modifier to be 0, so if someone does 'getfb2(&cmd); addfb2(&cmd);' they
> > would get an error from the addfb2().
> 
> My thinking is that since the primary userspace for this doesn't have
> symmetry with add (args for add, struct for get), that it was better
> to feed in INVALID directly. This is going to change, e.g., X server
> to:
>   modifier = (fb->flags ? DRM_MODE_FB_MODIFIERS) ? fb->modifier :
> DRM_FORMAT_MOD_INVALID;
> 
> It's a good point about the symmetry though. Do you know of direct
> non-libdrm users? Apart from igt of course ;)

Nope. Just thought that since both take the same struct it'd make some
sense. And figured it could serve as a quick sanity check to make sure
getfb outputs sane data. Or rather, if the driver accepts it back in
it can't be all bad at least.

But if you think it's not a particularly useful thing to do then I'm
certainly willing to accept that.

-- 
Ville Syrjälä
Intel OTC