RFC: what to do with ums when the X server is not suid root ?

Matthew Garrett mjg59 at srcf.ucam.org
Mon Jan 20 16:09:23 UTC 2014

On Mon, Jan 20, 2014 at 04:48:55PM +0100, Hans de Goede wrote:
> Hi,
> On 01/20/2014 03:18 PM, Matthew Garrett wrote:
> >-mga is probably also still relevant in some small number of cases.
> Don't we've a kms driver for those? Or you mean for mga cards not supported by
> the kms driver?

The KMS driver only supports the g200 cores embedded in some server 
chipsets, it doesn't handle real hardware. We've already dropped 3D 
support for those chips, though, so it's arguably not of great 
importance. The only real difference in functionality by dropping -mga 
would be losing multihead support, and I don't think anyone ever made 
that work on the UMS driver without the HAL blob.

> >We can probably kill -cirrus. That would leave -openchrome, which I think
> >is probably only really relevant for OLPC? What's the situation with the
> >binary nvidia and amd drivers?
> Oh, I completely did not think about the binary drivers yet. Ugh. AFAIK those
> are not compatible with kms, so the helper for other ums drivers would just do
> the right thing there since there would be no kms capable card to be found in /dev.

The binary drivers don't need iopl(), so the only real question is 
whether they need root for anything else. It may just be permissions on 
device nodes, in which case we can probably just special-case them?

> >It's probably worth considering whether porting uvesafb to kms would be
> >worthwhile, and then just using -modesetting.
> Yes that is something I was thinking about too, that would be an interesting approach,
> it would make it somewhat harder for people to use binary drivers, but not impossible.

I don't see it being any harder than the blacklisting of nouveau/radeon 
that's already required.

> And then we could simply forget about supporting ums at all I guess.

That would be certainly be a glorious flying-car future.

Matthew Garrett | mjg59 at srcf.ucam.org

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