[mythtv-users] Experience with upgrade of Xubuntu 18.04 to 20.04

[Tim Pletcher]

I recently upgraded one of my Xubuntu 18.04 MythTV v31-fixes machines to
the latest 20.04 Xubuntu release.  For the most part, the upgrade was
painless but there were a few issues I had to navigate through afterwards.
The issues were not specific to mythtv but impacted the functionality as a
frontend none-the-less.

The involved frontend uses intel VAAPI graphics and a MCEUSB infrared
receiver via kernel driver and ir-keytable for receiving remote control
input.

*First Issue:*
After the upgrade, I found mythfrontend would immediately segfault when
starting.  After troubleshooting, I discovered that this issue was actually
more broadly affecting any opengl application as glxgears would also show a
black screen and eventually segfault. Fortunately, glxgears provided
reference segementation fautl in iris_dri.so in the associated lines in
syslog whereas with mythfrontend oddly showed nothing in syslog or
mythfrontend.log associated with the segfault.

I use a xorg.conf file on this machine to manually specify an edid file and
to also force the preferred mode to 1920x1080p @ 54.94hz for judderless
playback with NTSC television.  I found that if any xorg.conf file is
present (even with nothing more than a simple DEVICE section present
specifying intel driver and no other options), then a segfault occurs in
opengl applications. Apparently, the latest Iris (Gallium3D) driver is the
default in Mesa 20.0 and some bug in the Iris driver impacts this
combination. In this case, a workaround to allow use of a xorg.conf with
intel graphics and allow opengl programs to run is to preface the startup
command like so:
   $ MESA_LOADER_DRIVER_OVERRIDE=i965 mythfrontend
One can also just remove the xorg.conf file altogether losing any
customizations and then opengl programs will run without issue using the
intel driver.

*Second issue:*
ir-keytable has undergone several changes and now uses a different format
for keymap files. Keymap files residing in /etc/rc_keymaps now have a .toml
extension and the required layout and syntax have changed.  Therefore, if
you have done any customization of /etc/rc_maps.cfg or have generated any
custom keymaps in /etc/rc_keymaps, those will have to be updated to work
with the latest required format.  I can elaborate more on the specific
changes but would just suggest reading the man files or looking at the
other packaged examples as a start.

My guess is that if using a default installation with little to no
customization, then the upgrade will be seamless. You will only have
add/enable the 20.04 mythbuntu repo post upgrade and update.

I haven't performed the 18.04 --> 20.04 upgrade on my combined
frontend/backend that uses nvidia graphics and lirc for remote control.
When I get around to it, I will share anything noteworthy that I encounter
with that machine as well. My BE/FE has many other duties and I will
probably hold off on that one for a while.

-Tim
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