choose-root

#!/bin/sh -e

PREREQS="udev"

prereqs() { echo "$PREREQS"; }

case "$1" in
    prereqs)
    prereqs
    exit 0
    ;;
esac

# $Id: choose_best_dproot 22 2012-04-22 16:25:18Z  $
#
# Graeme Vetterlein 21Apr2012 Choose the 'best' filesystem for dreamplug root
# Graeme Vetterlein 02Jul2023 Minor changes to use this on a QNAP412
#
# On the Dreamplug, we could specify ROOT (via jtag or vai setenv) and so set ROOT=foo
# On QNAP we can't set the root, so it's hardcoded to the word "root"
#
# On QNAP: My initrd file /conf/param.conf contains: ROOT="/dev/disk/by-uuid/0cc913c1-da92-4767-ba55-a56f57f88bdc"
# (but we have no simple way to set that value)
#
# So we can override the ROOT= setting by adding lines to /conf/param.conf
# 
# So assume /conf/param.conf contains: ROOT="/dev/disk/by-uuid/0cc913c1-da92-4767-ba55-a56f57f88bdc"
# We might add a line like ROOT=/dev/disk/by-label/root9
# 
# This will change the root filesystem mounted. But to be clear. The Kernel and the initrd will
# be the one stored in Flash on the Qnap but the root will be the one we mount, then it contains /etc/fstab
# this can cause /var /home /boot etc to be mounted, typically the same harddisk at /root.
# 
# So why did we choose ROOT=/dev/disk/by-label/root9?
# 
# On the Dreamplug we could "seed" this value, but in QNAP (without a JTAG) we can't easliy do so
# 
# So we need to be more heavy handed. If we find any /dev/disk/by-lable/root<n> we use them
# and ignore the incomming ROOT= , otherwise we use the ROOT= provided.
#
# Then we scan /dev/disk/by-label/root* looking for root0, root1 ... root9 we chose the highest numbered one.
#
# This allows you to have a good root filesystem stored on bays 1-4 and another
# one stored on an external HDD/SSD (tested with eSATA on TS412, but should work
# with USB drives) the if we have an external SSD with a root filesystem labeled
# root7 it will choose root7, then we can unplug the SSD and and it might choose
# root4. We could pull out the bay and it might choose root3 and so on.
#
#
# Who	When	What
# GPV	21Apr12	Created initial script , booting from external SD card
# GPV	02Jul23	For QNAP need to be more heavy-handed, since we lack a JTAG ...IFF we find LABEL=root[0-9] we override ROOT= otherwise we leave it untouched
# GPV	30jul23	There was a stupid "break" that meant ti took the 1st root it found (not the highest)
# GPV   30jul23 Removed comment , so actual update will be made to /conf/param.conf"

# Log via kernel ring buffer (use dmesg) ... comment out while testing as non root

# Bash only
#exec > >(tee "/dev/kmsg") 2>&1

# comment out while debugging

echo "choose_root incoming ROOT=${ROOT}"

exec > /dev/kmsg 2>&1



if [ -n "${ROOT}" -a -b "${ROOT}" ] ; then
    echo "FYI incoming ROOT=$ROOT is a valid block device."
else
    echo "FYI incoming ROOT=$ROOT is NOT a valid block device, unless we find an alternate, boot will fail"
fi

NEWROOT=""

# Bash only
#typeset -i suffix
#typeset -i thissuffix

prefix="/dev/disk/by-label/root"	# /dev/disk/by-label/root
suffix=0

choices=${prefix}[0-9]	   # eg /dev/disk/by-label/root1, /dev/disk/by-label/root2, /dev/disk/by-label/root4

for choice in ${choices}
do
    echo "choice=$choice"
    # Above will shell expand if possible, but is taken literally iff NOTHING matches
    if [ "${choice}" = "${prefix}[0-9]" ] ; then
	echo "There are no suitable alternatives root labels ${choice}"
	break
    fi

    thissuffix=${choice##${prefix}}

    if [ "${thissuffix}" -ge "${suffix}" ] ; then  # Only consider higher numbers
	if [ -b $choice ] ; then
	    echo "Found $choice is valid block device, candidate for ROOT"
	    sleep 1
	    NEWROOT=$choice

	fi
    else
	echo "ignoring $choice suffix is lower"
    fi
done


echo "NEWROOT=$NEWROOT"
if [ -z "$NEWROOT" ] ; then
    echo  "No new root was discovered, we will allow old style boot to continue"
else
    echo "Selected ${NEWROOT} as root"
    echo "write ROOT=\"${NEWROOT}\" to /conf/param.conf"
    echo "ROOT=\"${NEWROOT}\"" > /conf/param.conf  ### not we don't concat, we overwrite ... two ROOT stops boot
    echo "here is /conf/param.conf"
    cat /conf/param.conf
fi
exit 0