[klibc] [PATCH] isatty(): use TCGETS instead of TIOCGPGRP, like dietlibc does

Maciej Żenczykowski zenczykowski at gmail.com
Wed Jun 11 11:21:15 PDT 2014

Does ctrl+c work?

My experience with (non klibc) init=/bin/bash is that getting ctrl+c
to work requires some jumping through hoops, because running as pid 1
doesn't really work.

If I recall correctly you have to call setsid, and open a tty as a
controlling tty, you can't call setsid as pid 1.

The hack that I got to work (for reference, I'm using this for raw
kernel testing qemu-kvm) is:

kernel command line:  init=/boot/mz-boot.sh

$ cat /boot/mz-boot.sh
main() {
  echo 'Init (hostname, HOSTNAME, INPUTRC, HOME, LOGNAME, USER,
USERNAME, BASH_ENV, TERM, proc, fsck)'
  hostname linuxvm
  export HOSTNAME=linuxvm
  export INPUTRC=/etc/inputrc
  export HOME=/root
  export LOGNAME=root
  export USER=root
  export USERNAME=root
  export BASH_ENV=/root/.bashrc
  export TERM=xterm
  mount -t proc proc /proc
  fsck /dev/sda1
  fsck /dev/sda3

  echo 'Allowing safe editing of boot script.'
  mount -o remount,rw /
  mv -f /boot/mz-boot.sh /boot/mz-boot.sh_
  cp -p /boot/mz-boot.sh_ /boot/mz-boot.sh
  mount -o remount,ro /

  echo 'Turning up networking.'
  ip link set eth0 up
  ip addr add broadcast + dev eth0
  ip route add default via

  echo 'Starting shell.'
  echo '2nd (fallback) shell, just exit.'
  /bin/bash < /dev/ttyS0 > /dev/ttyS0 2> /dev/ttyS0

  echo 'Turning off networking.'
  killall sshd
  ip route del default
  ip addr del broadcast + dev eth0
  ip link set eth0 down

  echo 'Sync and unmount.'
  mount -o remount,ro /

  echo 'Poweroff.'
  /sbin/halt -d -f -p

main "$@"; exit

it's important that shell-to-bash doesn't get execed, put
fork-and-execed, cause it won't work as pid 1.

execve("/boot/shell-to-bash", ["/boot/shell-to-bash"],
["HOSTNAME=linuxvm", "TERM=xterm", "HOSTTYPE=i486", "PWD=/",
"PS1=\\h:\\w# ", "SHLVL=1", "HOME=/root", "OSTYPE=linux-gnu",
"MACHTYPE=i486-pc-linux-gnu", "_=/usr/bin/strace"]) = 0
setsid()                                = 1216
close(2)                                = 0
close(1)                                = 0
close(0)                                = 0
open("/dev/ttyS0", O_RDONLY)            = 0
open("/dev/ttyS0", O_WRONLY|O_NOCTTY)   = 1
open("/dev/ttyS0", O_WRONLY|O_NOCTTY)   = 2
execve("/bin/bash", ["bash"], ["HOME=/root", "TERM=xterm"]) = 0

I'm not sure how much of the above is relevant to /dev/console as
opposed to the /dev/ttyS0 I've obviously been using.

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