Dynamically transfer DRM lease between clients

Close for LL 12.0.0

The stealing (renamed to lease transition) functionality as described above (without the configuration file settings, which depends on https://lf-automotivelinux.atlassian.net/browse/SPEC-3815#icft=SPEC-3815) has been pushed to gerrit.

Lease transition has been tested with both weston and kmscube can perform a no blank transition from weston to kmscube and kmscube to kmscube.  Transitions to weston still see a black screen on transition because weston displays a black screen as its first frame.  This is because weston starts to display frames before the desktop-shell application is launched.

There is a patch pending merge upstream to fix this, which will allow seamless transition to weston, but it is blocked because it causes failures in the weston test suite.  I looked into the problem, and it seems to be an underlying problem with wayland.
Specifically with the patch applied, the wayland display event loop does not exit as expected when running the test suite (this doesn't affect the actual weston compositor shutdown).  An issue has been opened on the wayland gitlab to look into this.

I will push the weston patch to gerrit too, since it seems likely to be merged upstream once the wayland issue is fixed.

@Naoto YAMAGUCHI, thank you for your comments.

>> Should the stealing be prohibited (by the DRM lease manager) for other clients?

> This case can control container isolation. Which lease can use, it can control by socket binding to guest. It's my understanding.
In this case, DRM lease manager may not stealing be prohibited.

Container isolation may not be enough to prohibit stealing because any client in the container will be able to steal the lease.
The lease could also be stolen by the host.

For containers / environments that don't need the stealing feature, it might be useful to be able to disable stealing.  Then the clients don't have
to worry about it at all.

It is easy to add a global (applied to all DRM leases) enable/disable flag to the DRM lease manager. 
If the configuration file from SPEC is implemented, we can also enable/disable stealing per lease, so we can, for example, enable stealing on IC and disable it on IVI containers.

Maybe this is overkill (over spec) for the current IC use case though, what do you think?  

I agree to this point.

> this would only be used to transition away from a custom made IC specific client.

> Will the DRM lease transition feature only be used to switch from custom IC clients?

Exactly. This use case is limited.

> Should the stealing be prohibited (by the DRM lease manager) for other clients?

This case can control container isolation. Which lease can use, it can control by socket binding to guest. It's my understanding.
In this case, DRM lease manager may not stealing be prohibited.

Cool, thanks for looking into it!. I guess if this stealing process only happens with some custom clients made that are only intended to run in IC, then there shouldn't be a problem for the IVI side of things (where weston/libweston runs in) so that's why I've wanted to clarify things a bit.