[PATCH v7] unstable/drm-lease: DRM lease protocol support

Drew DeVault sir at cmpwn.com
Fri Oct 18 11:54:50 UTC 2019

On Fri Oct 18, 2019 at 12:21 PM Pekka Paalanen wrote:
> One thing I did not know the last time was that apparently
> systemd-logind may not like to give out non-master DRM fds. That might
> need fixing in logind implementations. I hope someone would step up to
> look into that.
> This protocol aims to deliver a harmless "read-only" DRM device file
> description to a client, so that the client can enumerate all DRM
> resources, fetch EDID and other properties to be able to decide which
> connector it would want to lease. The client should not be able to
> change any KMS state through this fd, and it should not be able to e.g.
> spy on display contents. The assumption is that a non-master DRM fd
> from a fresh open() would be fine for this, but is it?

What I do for wlroots is call drmGetDeviceNameFromFd2, which returns the
path to the device file, and then I open() it and use
drmIsMaster/drmDropMaster to make sure it's not a master fd. This seems
to work correctly in practice.

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