Re: Question on conversion from initrd to initramfs (1/2027 initrd support drop from kernel)

#!/bin/sh

# Wrapper init script for Tritech Service System
# Version 1.6 (2018-07-21)

# This script is responsible for unpacking the system
# into a tmpfs instance and switching into it.
# We must do this because initramfs is a ramfs instance
# which will crash the system if it accidentally fills.
# Packages that make up the system are put into place
# by this script, including kernel modules and firmware.

# The general procedure is as follows:
# 1. Mount a tmpfs instance to unpack to
# 2. Copy critical packages that are included in the wrapper
#    to the tmpfs instance
# 3. Unpack package files in wrapper's /packages folder
# 4. Unpack kernel modules and firmware
# 5. Copy the home skeleton archive to the /etc/init folder
# 6. Switch into the tmpfs root permanently.
# If the last step fails, a failsafe shell will launch.

# Failsafe shell if init terminates prematurely
trap 'exec /bin/sh' EXIT

export PATH=/bin:/sbin:/usr/bin:/usr/sbin

mkdir -p /proc /sys /dev /mnt
mount -t devtmpfs devtmpfs /dev
mount -t proc proc /proc
mount -t sysfs sysfs /sys

# Set all CPUs to maximum performance (if possible)
for X in /sys/devices/system/cpu/cpu*/cpufreq/scaling_governor
	do
	test -e "$X" && echo "$MODE" > $X 2>/dev/null
done

V=0
INIT=/init

for X in $(tr ' ' '\n' < /proc/cmdline)
	do case $X in
		debug-init) V=1; echo "TSS init debugging enabled" ;;
		root=*) ROOT=$(echo $X | sed 's/.*=//') ;;
		init=*) INIT=$(echo $X | sed 's/.*=//') ;;
	esac
done

# Root filesystem override capability for supporting "traditional" roots.
if [ ! -z "$ROOT" ]
	then echo "Root device override: $ROOT"
	# Linux allows mount by UUID but we need to verify it exists before trying.
	test ! -e $ROOT && ROOT=$(blkid | grep -i "UUID=\"$ROOT\"" | sed 's/:.*//')
	if [ -e $ROOT ]
		then mount -t auto $ROOT /mnt && \
		unset V X lzo gz bz2 xz lzma FLIST DECOMP ROOT BN && \
		umount /proc /sys /dev 2>/dev/null && \
		test -x /mnt/$INIT && exec /sbin/switch_root /mnt $INIT "$@"
		echo "WARNING: Could not mount specified root device."
		else echo "WARNING: Could not mount specified root device."
	fi
fi

# Set up compressed swap for very low memory systems
setup_zramswap () {
	SZ=/sys/block/zram0
	DEV=/dev/zram0
	RAM=$(grep MemTotal /proc/meminfo | awk '{print $2}')
	grep -q "zramswap" /proc/cmdline || test $RAM -gt 500000
	echo $(expr $RAM \* 1024) > $SZ/disksize
	test ! -e $DEV && mknod $DEV b $(cat $SZ/dev | tr ":" " ")
	mkswap $DEV 2>/dev/null >/dev/null
	swapon $DEV 2>/dev/null >/dev/null
	unset DEV SZ RAM
}
### End functions

# For low memory systems, we need zram swap working as soon as possible
setup_zramswap

# Mount tmpfs into which the system will be unpacked
mount -t tmpfs newroot /mnt -o size=80%
mkdir -p /mnt/packages/installed

# Be resilient if normal compression tools aren't present
test -x /usr/bin/unxz && xz='/usr/bin/unxz -c'
test -x /usr/bin/xz && xz='/usr/bin/xz -dc'
test -x /usr/bin/unlzop && lzo='/usr/bin/unlzop -c'
test -x /bin/lzop && lzo='/bin/lzop -dc'
test -x /usr/bin/lzop && lzo='/usr/bin/lzop -dc'
test -x /bin/gunzip && gz='/bin/gunzip -c'
test -x /bin/gzip && gz='/bin/gzip -dc'
test -x /usr/bin/gzip && gz='/usr/bin/gzip -dc'
test -x /bin/bunzip2 && bz2='/bin/bunzip2 -c'
test -x /bin/bzip2 && bz2='/bin/bzip2 -dc'
test -x /usr/bin/bzip2 && bz2='/usr/bin/bzip2 -dc'

echo -n "Loading: "

# For packages included in this wrapper, the package files
# need to be copied to the new root manually to achieve
# the same effect as if they were unpacked normally.
# The fastest way to do this is to tar and untar with
# a pipe since it can use lists.
for X in /packages/installed/*
	do echo -n "."
	cp "$X" "/mnt/$X"
	tar -c -T "$X" 2>/dev/null | tar -C /mnt -xp 2>/dev/null || echo -n "[ERROR]"
done

for X in /packages/*.pkg.tar.* /modules.* /firmware.*
	do
	if [ -e "$X" ]
		then echo -n "."
		BN="$(basename "$X")"
		DECOMP="$(echo "$BN" | sed 's/.*\.//')"
		test "$DECOMP" = "txz" && DECOMP="xz"
		DECOMP="$(eval "echo \$$DECOMP")"
		FLIST="/mnt/packages/installed/$(echo "$BN" | sed 's/\.pkg\.tar\.[a-z]*$//')"
		if eval $DECOMP "$X" | tar -C /mnt -xvp > $FLIST 2>/dev/null
			then rm -f "$X"
			else return 1
		fi
	fi
done

mkdir -p /mnt/lib/modules/$(/bin/uname -r)
echo -n "."
test -e /home-skel.tar.gz && mv /home-skel.tar.gz /mnt/etc/init/
echo -n "."
test -e /mnt/etc/tss/version && rm -f /mnt/etc/tss/version
mv /version /mnt/etc/tss/
echo 'party time! =)'

# BusyBox init fallback support
for X in 1 2 3 4
	do test ! -e /mnt/dev/tty$X && mknod /mnt/dev/tty$X c 4 $X
done
test ! -x /mnt/etc/init.d/rcS && mkdir -p /mnt/etc/init.d && ln -s /bin/sh /mnt/etc/init.d/rcS

test "$V" = "1" && echo -e "\nEarly init debug shell." && /bin/sh

unset V X lzo gz bz2 xz lzma FLIST DECOMP ROOT

umount /proc /sys

# Switch into new root. This should generally never fail.
test -x /mnt/$INIT && exec /sbin/switch_root /mnt $INIT "$@"

# If there is no /init present, try /sbin/init
test -x /mnt/sbin/init && exec /sbin/switch_root /mnt /sbin/init "$@"

# Fall back to shells in the new root if that doesn't work out
echo "switch_root apparently could not run /init or /sbin/init"
echo "Trying to run a shell in the new root instead..."
test -x /mnt/bin/bash && exec /sbin/switch_root /mnt /bin/bash "$@"
test -x /mnt/bin/sh && exec /sbin/switch_root /mnt /bin/sh "$@"

###############################################################
# This section should never be reached.

echo "For some reason, switch_root couldn't be done at all."
echo "Since we can't proceed further because something is"
echo "wrong, you're getting dropped into an infinitely"
echo "respawning shell. Apologies for this awful inconvenience."

while true
	do sleep 1
	/bin/sh
done