patches and low-level development discussion

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 #!/bin/execlineb -WS1
# SPDX-License-Identifier: EUPL-1.2+
# SPDX-FileCopyrightText: 2024-2025 Alyssa Ross <hi@alyssa.is>

# avoid concurrent operation
cgroup-setup --leaf -- $1
piperw 3 4
background {
  fdclose 3
  fdmove 2 4
  inotifywait -e MODIFY /sys/class/tty/console/active
}
fdclose 4
importas -i inotifywait_pid !

foreground {
  if { fdmove 0 3 grep -qx "Watches established." }
  background { fdmove 0 3 cat }
  fdclose 3

  # Wait until inotifywait is ready before updating serial gettys,
  # so that changes won't be missed in between updating and starting
  # inotifywait.
  pipeline { s6-instance-list /run/service/serial-getty }
  pipeline { sort }
  fdmove -c 3 0

  redirfd -r 0 /sys/class/tty/console/active
  pipeline { tr " " "\n" }
  pipeline { sort }

  pipeline { comm -3 - /proc/self/fd/3 }
  forstdin -Ep line
  case -N $line {
    "	?tty[0-9]*" { }
    "	(.*)" {
      importas -i tty 1
      s6-instance-delete /run/service/serial-getty $tty
    }
  }
  s6-instance-create /run/service/serial-getty $line
}

# Block until the active consoles change, then let s6 restart us.
unexport EXECLINE_STRICT # https://skarnet.org/lists/skaware/2246.html
wait -- $inotifywait_pid