Re: [PATCH] fbdev: Remove udlfb driver

[Pekka Paalanen <ppaalanen@gmail.com>]

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On Wed, 2 Dec 2020 08:55:52 +0100
Thomas Zimmermann <tzimmermann@suse.de> wrote:

> Hi
> 
> Am 01.12.20 um 12:20 schrieb Mikulas Patocka:
> > 
> > 
> > On Tue, 1 Dec 2020, Thomas Zimmermann wrote:
> >   

...

> >> And why can links not run as DRM master mode? If it renders to the terminal,
> >> it should act like a composer. In that case it almost certainly wants master
> >> status.
> >>
> >> Best regards
> >> Thomas  
> > 
> > How can a userspace program acquire master mode without being suid?  
> 
> For my understanding, there's no easy solution to that. :/

Hi,

there are several ways, though whether they are "easy" depends on your
mindset.

The best thing is to connect to logind D-Bus API and ask that for
session control, set up your session, and logind will open all input
and DRM devices for you, and logind will even handle most of the
complicated setup, DRM master and VT-switching for you.

Or, if no-one else has the DRM device open and you open it, you
automatically become DRM master. AFAIU, after recent kernel changes, it
is even possible to use dropMaster and setMaster after this without
being root, as long as you once in the file description lifetime had
DRM master.

Since this is about switching from fbdev to KMS API, you already have
all the tricky, complicated, arcane code to deal with tty setup and
VT-switching.

However, doing all that patching to all apps you want to use is such an
effort, that I'd ask if it would not be easier to just run a
light-weight Wayland compositor and run your apps in Wayland mode. Of
course, that requires choosing apps that run on Wayland to begin with,
so maybe it's not for you.


Thanks,
pq

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