[Wayland-bugs] [Bug 73782] Weston called from weston-launch loses permission to uaccess fb devices on tty switch back

[bugzilla-daemon]

https://bugs.freedesktop.org/show_bug.cgi?id=73782

Pekka Paalanen  changed:

   What|Removed |Added

 Resolution|--- |FIXED
 Status|NEW |RESOLVED

--- Comment #9 from Pekka Paalanen  ---
Ok, let's assume it's fixed then. Thanks.

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[Wayland-bugs] [Bug 73782] Weston called from weston-launch loses permission to uaccess fb devices on tty switch back

[bugzilla-daemon]

https://bugs.freedesktop.org/show_bug.cgi?id=73782

--- Comment #8 from n3rdopolis  ---
I think this can be closed, I have not replicated this in years (although I am
not using weston-launch)

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[Wayland-bugs] [Bug 73782] Weston called from weston-launch loses permission to uaccess fb devices on tty switch back

[bugzilla-daemon]

https://bugs.freedesktop.org/show_bug.cgi?id=73782

--- Comment #7 from Pekka Paalanen ppaala...@gmail.com ---
David Herrmann explains:
http://lists.freedesktop.org/archives/wayland-devel/2015-May/021998.html

Can you solve your problem with that information?

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[Wayland-bugs] [Bug 73782] Weston called from weston-launch loses permission to uaccess fb devices on tty switch back

[bugzilla-daemon]

https://bugs.freedesktop.org/show_bug.cgi?id=73782

--- Comment #6 from nerdopol...@verizon.net ---
Could anyone think of a better fix, or should I attempt to send my workaround
patch to the mailing list.


keep in mind to reproduce this issue, you need to add a 
SUBSYSTEM==graphics, KERNEL==fb*, TAG+=uaccess
line to a /lib/udev/rules.d/ file

(and not manually grant the user permissions to the framebuffer)
and then switch ttys back and forth

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[Wayland-bugs] [Bug 73782] Weston called from weston-launch loses permission to uaccess fb devices on tty switch back

[bugzilla-daemon]

https://bugs.freedesktop.org/show_bug.cgi?id=73782

--- Comment #4 from nerdopol...@verizon.net ---
After some more testing, it seems that it's not giving udev a chance to do its
thing.

If I add 
sleep(1);
before
fb_fd = fbdev_frame_buffer_open(output, output-device, new_screen_info);
in fbdev_output_reenable

it seems I can get it to work.

To me this is a hackish kind of fix, and probably not an acceptable fix to be
merged, but I hope this finding is helpful.

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[Wayland-bugs] [Bug 73782] Weston called from weston-launch loses permission to uaccess fb devices on tty switch back

[bugzilla-daemon]

https://bugs.freedesktop.org/show_bug.cgi?id=73782

--- Comment #2 from nerdopol...@verizon.net ---
It's been while since I was last able to try this, sorry about the long delay,
but now it still seems to do the same thing.

The problem isn't that uaccess doesn't work at all, as I am able to start
Weston without changing permissions when I set.
SUBSYSTEM==graphics, KERNEL==fb*, TAG+=uaccess

I then am able to start Weston as another user on another TTY too.

The problem is when I switch back to the original TTY of the first Weston
server it seems to not handle the fact that it had previously lost permissions,
and dies once I switch back to its tty.

This doesn't need weston-launch to do it, as it's logind that is setting the
device permissions. And I think it even revokes existing access when switching
to another user.

Should it try to reopen the framebuffer device?

Full stack trace to come

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[Wayland-bugs] [Bug 73782] Weston called from weston-launch loses permission to uaccess fb devices on tty switch back

[bugzilla-daemon]

https://bugs.freedesktop.org/show_bug.cgi?id=73782

--- Comment #3 from nerdopol...@verizon.net ---
Created attachment 109294
  -- https://bugs.freedesktop.org/attachment.cgi?id=109294action=edit
Full backtrace of switching away from and back to a weston server using fbdev
when uaccess is enabled

This is the back trace of when I don't set any manual permissions on /dev/fb0,
and instead give it uaccess permissions with udev. Weston seems to not try to
reconnect with the framebuffer device, as it works until I switch ttys, and
then try to switch back.

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[Wayland-bugs] [Bug 73782] Weston called from weston-launch loses permission to uaccess fb devices on tty switch back

[bugzilla-daemon]

https://bugs.freedesktop.org/show_bug.cgi?id=73782

--- Comment #1 from Pekka Paalanen ppaala...@gmail.com ---
The difference here is that weston-launch (a setuid-root helper process) is
used to open DRM and input devices, but does not support opening legacy fb
devices AFAICT. The fbdev backend opens the fb device itself.

However, I am unsure what would be the right fix for the real issue of opening
/dev/fb - let weston-launch open it, or is there some race during VT switching
that could be fixed?

The very least weston should deal gracefully with the failure instead of
segfaulting.

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