termios: Support FreeBSD

[patmaddox]

This sets some variables necessary to support Tailscale's built-in sshd server on FreeBSD (tailscale/tailscale#6155).

I could use some help finishing this off. Current issues that I think are worth addressing:

• pkg/termios/termios_freebsd.go is a cp of pkg/termios/termios_darwin.go, with the addition of the go:build freebsd / +build freebsd lines.
  • Addressed by renaming to termios_bsd.go and conditionally building.
• pkg/termios/var_freebsd.go has a lot of duplication with pkg/termios/var_unix.go as well.
  • Addressed by moving some syscalls out of var_unix.go and into var_linux.go and var_darwin.go.

From what I can tell, CI doesn't currently verify FreeBSD.

#2421 says:

Remove cirrus ci: It was only used for verifying freebsd buildability. We are going to use github actions for that instead (#2419)

GitHub actions doesn't officially support FreeBSD as far as I know. The method I'm aware of requires you to run a FreeBSD VM inside of a MacOS instance. That's pretty janky.

Cirrus CI runs directly on FreeBSD machines, so it should probably be re-instated for FreeBSD verification.

I am willing to assist (re-)configuring FreeBSD CI on Cirrus.

[codecov]

Codecov Report

Base: 73.66% // Head: 73.66% // Increases project coverage by +0.00% 🎉

Coverage data is based on head (b057145) compared to base (7e76d6f).
Patch coverage: 100.00% of modified lines in pull request are covered.

❗ Current head b057145 differs from pull request most recent head 027ebb5. Consider uploading reports for the commit 027ebb5 to get more accurate results

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2544   +/-   ##
=======================================
  Coverage   73.66%   73.66%           
=======================================
  Files         405      405           
  Lines       41231    41234    +3     
=======================================
+ Hits        30374    30377    +3     
  Misses      10857    10857           

Impacted Files	Coverage Δ
pkg/termios/sgtty_unix.go	0.00% <ø> (ø)
pkg/termios/var_linux.go	100.00% <100.00%> (ø)

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[rminnich]

This sure looks good to me. If you can make cirrus CI
work it would be nice to have freebsd CI back. Help wanted :-)

[rminnich]

from what I've seen, ttyio is always going to be a maze, I think this is about as good a job as can be done. Thanks again.

[patmaddox]

Removed unnecessary build line from var_freebsd.go, and rebased off of main.

[patmaddox]

This sure looks good to me. If you can make cirrus CI work it would be nice to have freebsd CI back. Help wanted :-)

Cool! Happy to do it. Would you like to see it as part of this PR, or a separate one?

Edit: Based on the number of failures, it should probably be a separate PR. I suspect there will be a lot of stub implementations on FreeBSD that serve as a TODO list for full support.

[rminnich]

yeah, let's do a separate PR, and thanks in advance for the issues we are certain to see :-)

I will help whereever I can.