whatsmyboot

#!/bin/sh
# whatsmyboot (part of ossobv/vcutil) // wdoekes/2024 // Public Domain
#
# Figure out which boot and/or root drive(s) we're using.
#
# This looks to be non-trivial on various systems. This script uses the
# following heuristics:
# - Check efibootmgr -v and read HD(n,GTP,uuid) entries;
# - If not found, ask df where /boot is;
# - If found, check for ZFS and extract source disks.
# Lastly, the partitions are converted to drives by querying udevadm.
#
# Use -r to find the root drives. If you want to exclude drives for e.g. full
# disk encryption, use `whatsmyboot -a` to find both boot and root drives to
# exclude.
#
# USAGE:
#
#   # whatsmyboot [-r|-a]
#   /dev/sda
#   /dev/sdb
#

set -eu

_pathboots() {
    local path
    path="$1"
    local dev type partitions
    partitions=$(\
        df -l --output=source,fstype "$path" | sed -e1d |
        while read dev type; do
            if test "$dev" != "${dev#/}"; then
                echo "$dev"
            elif test "$type" = "zfs"; then
                zpool status -LP "${dev%%/*}" |
                    awk 'substr($1,1,5)=="/dev/"{print $1}'
            else
                echo "$0: Not implemented: $dev $type" >&2
                exit 1
            fi
        done
    )
    if test -n "$partitions"; then
        echo "$partitions"
    else
        echo "$0: No BIOS partitions?" >&2
        exit 1
    fi
}

biosboots() {
    _pathboots /boot
}

efiboots() {
    local efiout
    if efiout=$(efibootmgr -v 2>/dev/null) && test -n "$efiout"; then
        local partitions
        partitions=$(printf '%s\n' "$efiout" | awk '
            /^BootOrder:/{split($2,boots,",")}
            /^Boot[0-9].*HD[(][0-9]*,GPT,/{
              idx=substr($1,5,4);gsub("^.*HD[(][0-9]*,GPT,","");gsub(",.*","");
              bs[idx]=$0}
            END{for(bidx in boots){if(bs[boots[bidx]])print bs[boots[bidx]]}}
        ' | xargs -IX blkid -o device --match-token=PARTUUID=X | uniq)
        if test -z "$partitions"; then
            echo "$0: EFI, but no boot partitions found?" >&2
            exit 1
        fi
        echo "$partitions"
    elif test -d /sys/firmware/efi; then
        echo "$0: EFI directory found, but efibootmgr failed?" >&2
        exit 1
    fi
}

boot_partitions() {
    local out
    out=$(efiboots)
    if test -n "$out"; then
        echo "$out"
    else
        biosboots
    fi
}

root_partitions() {
    _pathboots /
}

partitions_to_devices() {
    # awk '
    # /^\/dev\/nvme/{
    #   gsub("p[0-9]+$", "");if(!($0 in uniq))print $0;uniq[$0]=1}
    # /^\/dev\/sd[a-z]/{
    #   gsub("[0-9]+$", "");if(!($0 in uniq))print $0;uniq[$0]=1}
    # !/^\/dev\/(nvme|sd[a-z])/{if(!($0 in uniq))print $0;uniq[$0]=1}
    # '
    local partition tmp dev dirname
    while read partition; do
        tmp=$(udevadm info --query=property --name="$partition" |
            grep ^DEVPATH=)
        if test -z "$tmp"; then
            echo "udevadm fail on $partition" >&2
            exit 1
        fi
        tmp=${tmp%/*}
        dev=${tmp##*/}

        # Is this mdadm? Then we have to translate some more.
        if test "$dev" != "${dev#md}"; then
            grep "^$dev[[:blank:]]" /proc/mdstat | tr ' ' '\n' |
               sed -e '/[[]/!d;s/[[].*//;s@^@/dev/@' |
               partitions_to_devices
        # Is this nvme? Then strip the namespace.
        elif test "$dev" != "${dev#nvme}"; then
            tmp=${tmp%/*}
            dev=${tmp##*/}
            echo "/dev/$dev"
        else
            echo "/dev/$dev"
        fi
    done | awk '{if(!($0 in uniq)){print;uniq[$0]=1}}'
}

boot_devices() {
    boot_partitions | partitions_to_devices
}

root_devices() {
    root_partitions | partitions_to_devices
}


if test $# -eq 0; then
    data=$(boot_devices || true)
elif test $# -eq 1 && test "$1" = "-r"; then
    data=$(root_devices || true)
elif test $# -eq 1 && test "$1" = "-a"; then
    data=$( { boot_devices && root_devices; } | sort -u )
else
    echo "usage: $0 [-r|-a]" >&2
    exit 1
fi

if test -z "$data"; then
    echo "$0: Detection failure" >&2
    exit 1
fi

echo "$data"