gpt2mbr

gpt2mbr.sh

#!/bin/bash -e
# Copyright (C) 2015 Endless Mobile, Inc.
# Licensed under the GPLv2

[ $# -lt 1 ] && exit 1

# TODO: check if in use
# TODO: parse both /dev/sdaX or sdaX
# TODO: check if partition contains EOS
# TODO: check if we are passing a partition and not a disk

get_last_char() {
	ret=$1
	while [ "${#ret}" != "1" ]; do
		ret=${ret#?}
	done
	echo $ret
}

root_part=$1
partno=$(get_last_char ${root_part})
swap_partno=$((partno + 1))
esp_partno=1

root_disk=${root_part%?}
swap_part=${root_disk}${swap_partno}
esp_part=${root_disk}${esp_partno}

esp_part_dev=${esp_part#/dev/}
root_disk_dev=${root_disk#/dev/}

if [ -z "${root_disk}" ]; then
  echo "eos-gpt2mbr: no root disk found for $root_part"
  exit 0
fi

# udev might still be busy probing the disk, meaning that it will be in use.
udevadm settle

# take current partition table
parts=$(sfdisk -d $root_disk)

# check the last partition on the disk
lastpart=$(echo "$parts" | sed -n -e '$ s/[^:]*\([0-9]\) :.*$/\1/p')

if [ $lastpart -eq $swap_partno ]; then
  # already have an extra partition, perhaps we were halfway through creating
  # a swap partition but didn't finish. Remove it to try again below.
  parts=$(echo "$parts" | sed '$d')
elif [ $lastpart -gt $swap_partno ]; then
  echo "repartition: found $lastpart partitions?"
  exit 0
fi

# remove ESP
parts=$(echo "$parts" | sed -e "/$esp_part_dev/d")

# calculate new partition sizes
disk_size=$(blockdev --getsz $root_disk)
part_size=$(blockdev --getsz $root_part)
part_start=$(echo "$parts" | sed -n -e '$ s/.*start=[ ]\+\([0-9]\+\).*$/\1/p')
part_end=$(( part_start + part_size ))
echo "Dsize $disk_size Psize $part_size Pstart $part_start Pend $part_end"

# Calculate the new root partition size, assuming that it will expand to fill
# the remainder of the disk
new_size=$(( disk_size - part_start ))

# If we find ourselves with >100GB free space, we'll use the final 4GB as
# a swap partition
added_space=$(( new_size - part_size ))
if [ $added_space -gt 209715200 ]; then
  new_size=$(( new_size - 8388608 ))
  swap_start=$(( part_start + new_size ))

  # Align swap partition start to 1MB boundary
  residue=$(( swap_start % 2048 ))
  if [ $residue -gt 0 ]; then
    swap_start=$(( swap_start + 2048 - residue ))
    # might as well bump up root partition size too, instead of leaving a gap
    new_size=$(( new_size + 2048 - residue ))
  fi
fi

if [ $new_size -gt $part_size ]; then
  echo "Try to resize $root_part to fill $new_size sectors"
  parts=$(echo "$parts" | sed -e "$ s/size=[0-9\t ]*,/size=$new_size,/")
fi

if [ -n "$swap_start" ]; then
  # Create swap partition
  echo "Create swap partition at $swap_start"
  parts="$parts
start=$swap_start, type=0657FD6D-A4AB-43C4-84E5-0933C84B4F4F"
fi

# Reset partition indexes
parts=$(echo "$parts" | sed -e "s/${root_disk_dev}.//")

# GPT -> DOS
parts=$(echo "$parts" | sed -e "s/label: gpt/label: dos/")

# Remove GPT types and UUIDs
parts=$(echo "$parts" | sed -e "s/, type=.*//")

echo "$parts"
echo "$parts" | sfdisk --force --no-reread $root_disk
ret=$?
echo "sfdisk returned $ret"
udevadm settle

[ -e "$swap_part" ] && mkswap -L eos-swap $swap_part