Hi Scott,
On 2021/02/01 19:21, Scott Anderson wrote:
On 1/02/21 10:19 pm, Damian Hobson-Garcia wrote:
Hi all,
I am working on adding DRM lease support to a libweston based
compositor.
The compositor will be a client (lessee) that will display output to
a DRM lease that
is created by another (lessor) process, so this is kind of the
opposite direction to the DRM lease patches
that were submitted a while back [1].
The motivation is to be able to run multiple instances of weston w/
DRM backend, where each instance
has direct access to a subset of the DRM connectors. Each instance
could, for example, run in a separate container,
with minimal host interaction.
In this configuration the DRM lease would be received from a UNIX
domain socket connection to the lessor,
so would not discoverable via udev, in the same way that DRM device
nodes normally are.
I think that I would need to make changes to the compositor-drm, but
if possible,
I'd like to make those changes generic enough to be useful upstream
as well, so I was hoping to get some feedback before possibly heading
down a wrong path.
From what I can tell, I need to:
1. Get the DRM lease file descriptor, given an identifier (In my DRM
lease case this is a name that maps to a socket path)
2. Get a udev_device struct for the device corresponding to the above
fd (via the major:minor numbers)
I think that #1 can be implemented in either via the launcher API (a
new launcher type?) or by adding an option for
the compositor to provide the fd, but #2 seems like it should be in
compositor-drm, right?
Are there other use cases that would benefit from extending the
launcher / compostior APIs in this way?
or the udev device handle creation? Are there any plans/interest for
running the DRM backend from inside
a container?
Thank you,
Damian
[1]
https://lists.freedesktop.org/archives/wayland-devel/2018-February/037162.html
This doesn't answer any of your questions about Weston specifically,
but an alternative approach would be to add drm-lease support to
logind. It already has its own concept of groups of devices (seats),
so it would also solve any issues regarding who gets what input
devices, and the solution wouldn't be specific to weston. Any
logind-capable display server (i.e. all of them, including Xorg) would
be able to use this, without requiring any modification.
Scott
Thank you for your suggestion. I'm not too familiar with all of the
specifics of logind, but I will look into it. One thing that I noticed
though is that it looks like launcher-logind requests file descriptors
based on major and minor device numbers. Since all DRM leases
for a device share the same major/minor, it looks like the TakeDevice()
method might not be able to differentiate them. I'll look into it some
more.
Thank you,
Damian
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