[systemd-devel] starting qt application after DRM initialized

[Mantas Mikulėnas]

On Fri, Dec 7, 2018 at 9:36 AM Belisko Marek <marek.belisko at gmail.com>
wrote:

> Hi Tomasz,
>
> On Fri, Dec 7, 2018 at 6:26 AM Tomasz Torcz <tomek at pipebreaker.pl> wrote:
> >
> > On Thu, Dec 06, 2018 at 10:58:31PM +0100, Belisko Marek wrote:
> > > Hi,
> > >
> > > I'm trying to run qt qml application on intel nuc but when booted from
> > > hdd I'll get an eror when app is started:
> > >
> > > I think it is some kind of timing issue as when booting same image
> > > from usb stick application will automatically start while when booting
> > > from hdd I get above error. Would be possible to postpone it somehow
> > > until DRM display is initialized? Thanks.
> >
> >   This is exactly the problem GDM (GNOME Display Manager) encountered
> > few years ago. The solution was devised – your application needs to wait
> > until CanGraphical property goes to yes on the seat application is
> > using.
> Thanks for info. But I'm not suing any GDM (nor X) just qml
> application. So IIRC then I need to code something in my application
> to wait until
> CanGraphical is available?


Yes, to use this method you would need to access logind's D-Bus API. I'm
not sure whether QML provides D-Bus access, although Qt does.


> I was thinking about
> approach that systemd can postpone starting of my application until
> DRM is available (not sure is such trigger exists though).
>

It sounds more like you're looking for a dependency, not a trigger.
(Although either would work, I guess.)

In systemd itself, the only available built-in dependency is "device now
available in /dev or /sys". For example, you could use this, assuming
there's only one card and it's always called "card0":

[Unit]
Requires=dev-dri-card0.device
After=dev-dri-card0.device

(Note: This also needs udev/rules.d/99-systemd.rules to be extended with an
apropriate TAG+="systemd".)

-- 
Mantas Mikulėnas
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