/dev/ttynull and VT-less kernels on Desktop

[nerdopolis <bluescreen_avenger@verizon.net>]

Hi

I have been doing some testing on VT-less desktops. I brought up an issue with
how systemd was not logging to /dev/console because isatty() was failing (in a
thread last month which I kind of bungled by accidentally sending the first
message with rich text enabled by accident) I solved that issue though. As
disabling the VT console causes the default console to /dev/ttyS0 and the 
isatty() calls on it were returning false.

I have found out that this issue actually already has an existing solution in
the ttynull driver. After enabling it, and then adding console=ttynull to the
kernel command line, this allows isatty() to succeed on VT-less systems, and
now systemd is able to correctly log its status messages to the kernel console
on VT-less systems, without needing anything connected to /dev/ttyS0

However I have two questions:

1. Is there a build option to make it prioritize /dev/ttynull over /dev/ttyS0 ?

   It would probably be neeed so that distributions don't have to worry about
   the logistics of adding that to everyone's GRUB_CMDLINE_LINUX_DEFAULT come
   the eventual day the decide to go VT-less during its upgrade process.

2. Is there a good way for the userspace to know that /dev/ttynull is primary?

   "ttynull" doesn't seem to appear in /sys/devices/virtual/tty/console/active
   when it is active. Which seems like it could make sense, (as in a check if
   it is empty) however if I boot with "console=ttyS0 console=ttynull", "ttyS0"
   appears in the file, but if I boot with say "console=tty0 console=ttyS0",
   they both appear in the file. It would be nice if in the first case it would
   report "ttyS0 ttynull".

   With Plymouth, when the primary console is /dev/ttyS0 instead of /dev/tty0
   it defaults to serial logging instead of showing a graphical splash, so now
   if you want a graphical splash on a VT-less system, you have to also specify
   "plymouth.graphical" on the kernel command line. If it could see "ttynull"
   in the end of the file, distributions that go VT-less can also just enable
   "ttynull" as the default console, and Plymouth could use that to
   differentiate between VT-less desktop systems, or systems that actually want
   serial logging, so they don't have to change GRUB_CMDLINE_LINUX_DEFAULT.

Thanks