tinyramfs/lib/init.sh

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#!/bin/sh
#
# https://shellcheck.net/wiki/SC2154
# https://shellcheck.net/wiki/SC2034
# shellcheck disable=2154,2034
init_base()
{
mount -t proc -o nosuid,noexec,nodev proc /proc
mount -t sysfs -o nosuid,noexec,nodev sys /sys
mount -t tmpfs -o nosuid,nodev,mode=0755 run /run
mount -t devtmpfs -o nosuid,noexec,mode=0755 dev /dev
ln -s /proc/self/fd /dev/fd
ln -s fd/0 /dev/stdin
ln -s fd/1 /dev/stdout
ln -s fd/2 /dev/stderr
}
eval_hooks()
{
_type=$1
# https://shellcheck.net/wiki/SC2086
# shellcheck disable=2086
{ IFS=,; set -- $hooks; unset IFS; }
for _hook; do
[ -f "/lib/tinyramfs/hook.d/${_hook}/${_hook}.${_type}" ] || continue
[ "$rdbreak" = "$_hook" ] && panic "break before: ${_hook}.${_type}"
# https://shellcheck.net/wiki/SC1090
# shellcheck disable=1090
. "/lib/tinyramfs/hook.d/${_hook}/${_hook}.${_type}"
done
}
parse_cmdline()
{
# XXX /proc/cmdline can contain multiline data?
read -r cmdline < /proc/cmdline
# https://kernel.org/doc/html/latest/admin-guide/kernel-parameters.html
# ... parameters with '=' go into init's environment ...
for _param in $cmdline; do case $_param in
rdpanic) trap - EXIT ;;
rddebug) set -x ;;
# Maintain backward compatibility with kernel parameters.
ro | rw) rorw=$_param ;;
rootwait) root_wait=-1 ;;
--) init_args=${_param##*--}; break ;;
rootfstype=*) root_type=${_param#*=} ;;
rootflags=*) root_opts=${_param#*=} ;;
rootdelay=*) root_wait=${_param#*=} ;;
esac; done
}
mount_root()
{
[ "$rdbreak" = root ] && panic 'break before: mount_root()'
resolve_device "$root" "$root_wait"
# https://shellcheck.net/wiki/SC2086
# shellcheck disable=2086
mount \
-o "${rorw:-ro}${root_opts:+,$root_opts}" ${root_type:+-t "$root_type"} \
-- "$device" /mnt/root || panic "failed to mount rootfs: $device"
}
boot_system()
{
[ "$rdbreak" = boot ] && panic 'break before: boot_system()'
for _dir in run dev sys proc; do
mount -o move "/${_dir}" "/mnt/root/${_dir}" || :
done
# POSIX 'exec' has no '-c' flag to execute command with empty environment.
# Use 'env -i' instead to prevent leaking exported variables.
#
# Some implementations of 'switch_root' doesn't conform to POSIX utility
# guidelines and doesn't support '--'. This means that safety of init_args
# isn't guaranteed.
#
# https://shellcheck.net/wiki/SC2086
# shellcheck disable=2086
exec \
env -i TERM=linux PATH=/bin:/sbin:/usr/bin:/usr/sbin \
switch_root /mnt/root "${init:-/sbin/init}" $init_args ||
panic "failed to boot system"
}
# TODO add `quiet` support
# -e: Exit if command return status greater than 0
# -f: Disable globbing *?[]
set -ef
# Run emergency shell if init unexpectedly exiting due to error.
# TODO prompt to continue
trap panic EXIT
# https://shellcheck.net/wiki/SC1091
# shellcheck disable=1091
. /lib/tinyramfs/common.sh
# https://shellcheck.net/wiki/SC1091
# shellcheck disable=1091
. /etc/tinyramfs/config
init_base
parse_cmdline
eval_hooks init
mount_root
eval_hooks init.late
boot_system