On 18 December 2018 7:07:01 pm NZDT, Christopher James Halse Rogers
<ch...@cooperteam.net> wrote:
>On 18 December 2018 4:35:37 am AEDT, Emil Velikov
><emil.l.veli...@gmail.com> wrote:
>>Hi Christopher,
>>
>>On Tue, 20 Nov 2018 at 03:37, Christopher James Halse Rogers
>><christopher.halse.rog...@canonical.com> wrote:
>>>
>>> We can't use drmSetMaster to query whether or not a drm fd is master
>>> because it requires CAP_SYS_ADMIN, even if the fd *is* a master fd.
>>>
>>Can you please mention the exact use case here? You mentioned it over
>>IRC although it'll be nice to have it here for posterity.
>
>Certainly!
>
>The particular use-case I was hitting was testing my display server in
>a container, where container-root is not real-root but the
>implicit-master FD you get by opening the DRM node when there is no
>current master would be sufficient.
>
>Just assuming the FD we get is master and failing later breaks the
>platform probing; for example, when run under X11 if we don't check
>master we'll load the KMS platform and then fail, rather than noticing
>that KMS won't work and using our X11 backend.
>
>>
>>> Pick DRM_IOCTL_MODE_ATTACHMODE as a long-deprecated ioctl that is
>>> DRM_MASTER but not DRM_ROOT_ONLY as the probe by which we can detect
>>> whether or not the fd is master.
>>>
>>I'm wondering if we cannot extent DRM_IOCTL_GET_CLIENT or another
>>IOCTL.
>>What do you think? May I interest you in writing an RFC for the
>>kernel-side?
>
>I think if I was going to do kernel-side changes if probably just make
>it so that IOCTL_SET_MASTER just unconditionally succeeded on an fd
>that was already master?
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Ping!
Is there anything more you'd like to know about my use-case here? Are there any
objections to adding drmIsMaster()?
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