Hi Marius,
On 2021/02/02 19:51, Pekka Paalanen wrote:
On Tue, 2 Feb 2021 12:41:17 +0200
Marius Vlad <marius.v...@collabora.com> wrote:
On Tue, Feb 02, 2021 at 11:28:46AM +0200, Pekka Paalanen wrote:
On Tue, 2 Feb 2021 00:39:30 +0900
Damian Hobson-Garcia <dhobs...@igel.co.jp> wrote:
Hi Pekka,
Thank you for your comments.
On 2021/02/01 19:34, Pekka Paalanen wrote:
On Mon, 1 Feb 2021 18:19:29 +0900
Damian Hobson-Garcia <dhobs...@igel.co.jp> 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.
Hi,
that is an interesting goal. How will this "nested" Weston/DRM get
input?
This is still uncertain. One option is of course to bind mount input
devices into the
container, but I know that there are problems with providing the
seat information that libinput needs (unless that has changed recently).
I haven't really looked into how to address that yet.
Are you referring to not having access to udev daemon (the udev
properties mechanism) in the container?
If yes, there might be another problem below.
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?
Hmm, what would an udev_device be needed for? Hotplug events?
Yes, hotplug events. My hope is that it would work that same as for the
regular
DRM device nodes. I guess that some modifications to the hotplug code
may be
necessary to deal with events on connectors that are not included in the
DRM lease.
Hotplug events are udev events, and traditionally they do not name any
connetor or anything. They only say "something might have changed with
this DRM device, it would be better for you to re-scan the whole
device to see what changed". Weston implements this.
I'm not exactly sure how those events are delivered, do you need a udev
daemon running? Weston uses the udev_monitor API for it currently which
I think requires udevd maybe?
An alternative could be to deliver the equivalent of hotplug events
through your DRM leasing protocol.
I can't say anything for certain, but as a first try, I'd probably
attempt writing a new launcher backend for weston, parallel to the
existing launcher backends logind, weston-launch and direct. The device
discovery code is not in the launcher backend but in the DRM-backend
proper though, so I guess you indeed may need to do something about
that.
Would this mean modifying the launcher API to pass down a
file-descriptor directly, or would that happen in the launcher itself
(assuming that would be reason for writing a new launcher -- somehow use some
helpers to retrieve the lease fd in the container).
I think that you could just pass an identifier for the DRM lease you
want to the launcher
backend with and get back the lease fd. No changes
to the launcher API, or existing launcher backends would be necessary.
It would need a method to choose which launcher backend to use, though,
which is
currently determined at the weston_launcher_connect() stage. Maybe
adding a flag
in the API or based on the environment, like it is in the other backends?
Thank you,
Damian
Wouldn't be easier to just pass down the lease fd to the DRM-backend, as
config option, and handle the mapping itself in the compositor rather than in
libweston?
I don't know. Figuring out where the API should be and what it should
look like is the major unknown.
DRM fd is one thing. Something needs to cater for input devices too.
Also I don't know what their leasing protocol looks like, does it have
dynamic revocation and re-creation without shutting down Weston.
Thanks,
pq
You seem to be on the right track from what I can tell.
As for other use cases or running inside containers, nothing comes to
my mind, but OTOH the concept of something like "a full desktop in a
container" might be attractive to some? Or using a multi-head gfx card
for multi-seat, to avoid needing to have one gfx card per seat.
Thanks,
pq
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