tinyramfs/init

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#!/bin/sh
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#
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# tiny init
#
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# false positive
# shellcheck disable=2154
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print()
{
printf "%b %s\n" "${2:-"\033[1;37m>>\033[m"}" "$1"
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}
panic()
{
print "${1:-unexpected error occurred}" \
"\033[1;31m!!\033[m" >&2; sh
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}
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resolve_device()
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{
count=0; device="$1"
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case "${device%%=*}" in /dev/*) ;;
UUID) device="/dev/disk/by-uuid/${device#*=}" ;;
LABEL) device="/dev/disk/by-label/${device#*=}" ;;
PARTUUID) device="/dev/disk/by-partuuid/${device#*=}" ;;
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esac
# prevent race condition
# XXX what the hell happens here?
# why this loop sometimes trigger panic if i remove '|| :'
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while [ ! -b "$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
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# false positive
# shellcheck disable=1090
for hook in $hooks; do
[ -f "${hksdir}/${hook}/${hook}.${type}" ] || continue
. "${hksdir}/${hook}/${hook}.${type}"
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done
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}
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prepare_environment()
{
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# false positive
# shellcheck disable=1091
. /etc/tinyramfs/config
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export \
PATH=/bin TERM=linux SHELL=/bin/sh \
LANG=C LC_ALL=C PS1="# " HOME=/root
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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
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mount -t devtmpfs -o nosuid,noexec,mode=0755 dev /dev
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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
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}
parse_cmdline()
{
read -r cmdline < /proc/cmdline
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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
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}
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mount_root()
{
[ "$break" = root ] && { print "break before mount_root()"; sh; }
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resolve_device "$root"
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set -- \
"${rorw:--o ro}${root_opts:+,$root_opts}" \
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"${root_type:+-t $root_type}" "$device" "/mnt/root"
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# word splitting is safe by design
# shellcheck disable=2068
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mount $@ || panic "failed to mount root"
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}
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boot_system()
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{
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[ "$break" = boot ] && { print "break before boot_system()"; sh; }
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for dir in run dev sys proc; do
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mount -o move "$dir" "/mnt/root/${dir}"
done
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set -- "/mnt/root" "${init:-/sbin/init}" "$init_args"
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# POSIX exec has no -c flag to execute command with empty environment
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# use 'env -i' to prevent leaking exported variables
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# word splitting is safe by design
# shellcheck disable=2068
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exec env -i TERM=linux PATH=/bin:/sbin:/usr/bin:/usr/sbin \
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switch_root $@ || panic "failed to boot system"
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}
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# int main()
{
# enable exit on error and disable globbing
# trap EXIT signal
set -ef; trap panic EXIT
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prepare_environment
parse_cmdline
run_hook init
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mount_root
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run_hook init.late
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boot_system
}