tinyramfs/init

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#!/bin/sh
#
# tiny init
#
# false positive
# shellcheck disable=2154
print()
{
printf "%b %s\n" "${2:-"\033[1;37m>>\033[m"}" "$1"
}
panic()
{
print "${1:-unexpected error occurred}" \
"\033[1;31m!!\033[m" >&2; sh
}
resolve_device()
{
count=0; device="$1"
case "${device%%=*}" in
UUID) device="/dev/disk/by-uuid/${device#*=}" ;;
LABEL) device="/dev/disk/by-label/${device#*=}" ;;
PARTUUID) device="/dev/disk/by-partuuid/${device#*=}" ;;
/dev/*) ;;
*) return 0 ;;
esac
# prevent race condition
# XXX what the hell happens here?
# why this loop sometimes trigger panic if i remove '|| :'
while [ ! -b "$device" ]; do sleep 1
[ "$((count += 1))" = "${rootdelay:=30}" ] && {
panic "failed to lookup partition"
break
}
done || :
}
run_hook()
{
type="$1"; hksdir=/usr/share/tinyramfs/hooks
# run hooks if any
# false positive
# shellcheck disable=1090
for hook in $hooks; do
[ -f "${hksdir}/${hook}/${hook}.${type}" ] || continue
. "${hksdir}/${hook}/${hook}.${type}"
done
}
prepare_environment()
{
# false positive
# shellcheck disable=1091
. /etc/tinyramfs/config
export \
PATH=/bin TERM=linux SHELL=/bin/sh \
LANG=C LC_ALL=C PS1="# " HOME=/root
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
}
parse_cmdline()
{
read -r cmdline < /proc/cmdline
for line in $cmdline; do case "$line" in
rootfstype=*) root_type="${line#*=}" ;;
rootflags=*) root_opts="${line#*=}" ;;
debug=1) set -x ;;
ro | rw) rorw="-o $line" ;;
--*) init_args="${cmdline#*-- }"; break ;;
*=*) command export "$line" ;;
*) command export "${line}=1" ;;
esac 2> /dev/null || :; done
}
mount_root()
{
[ "$break" = root ] && { print "break before mount_root()"; sh; }
resolve_device "$root"
set -- \
"${rorw:--o ro}${root_opts:+,$root_opts}" \
"${root_type:+-t $root_type}" "$device" "/mnt/root"
# word splitting is safe by design
# shellcheck disable=2068
mount $@ || panic "failed to mount root"
}
boot_system()
{
[ "$break" = boot ] && { print "break before boot_system()"; sh; }
for dir in run dev sys proc; do
mount -o move "$dir" "/mnt/root/${dir}"
done
set -- "/mnt/root" "${init:-/sbin/init}" "$init_args"
# POSIX exec has no -c flag to execute command with empty environment
# use 'env -i' to prevent leaking exported variables
# word splitting is safe by design
# shellcheck disable=2068
exec env -i TERM=linux PATH=/bin:/sbin:/usr/bin:/usr/sbin \
switch_root $@ || panic "failed to boot system"
}
# int main()
{
# enable exit on error and disable globbing
# trap EXIT signal
set -ef; trap panic EXIT
prepare_environment
parse_cmdline
run_hook init
mount_root
run_hook init.late
boot_system
}