init-storage: Resize data partition

If the data volume is a partition (rather than a whole disk device), the
`init-storage` script will now attempt to resize it to use all
unallocated space on the disk.  This only works if it is the last
partition on the disk.  This situation is common when writing the
`sdcard.img` file directly to a disk that is larger than 4 GiB.

overlay/usr/libexec/init-storage

@@ -29,6 +29,22 @@ copy_var() {
 
 format_dev() {
     dev="$1"
+    partno=$(partition_number "${dev}")
+    if [ -n "${partno}" ]; then
+        disk="$(get_disk "${dev}")"
+        if [ -n "${disk}" ]; then
+            printf 'Resizing partition %d on disk %s\n' \
+                "${partno}" \
+                "${disk}" \
+                >&2
+            resize_partition "${disk}" "${partno}"
+        else
+            printf 'Could not find disk for device %s\n' \
+                "${dev}" \
+                >&2
+        fi
+    fi
+
     printf 'Creating BTRFS filesystem on %s\n' "${dev}"
     mkfs.btrfs "${dev}" || exit
 
@@ -41,12 +57,37 @@ format_dev() {
     umount "${dev}" || exit
 }
 
+get_disk() {
+    _syspath=/sys/class/block/${1##*/}
+    [ -d "${_syspath}" ] || return 1
+    if [ ! -f "${_syspath}"/partition ]; then
+        readlink -f "${1}"
+        return $?
+    fi
+    _disk=$(readlink -f "${_syspath}"/..)
+    if [ -n "${_disk}" ]; then
+        printf '/dev/%s\n' "${_disk##*/}"
+        return 0
+    fi
+    return 1
+}
+
 has_fs() {
     dev="$1"
     fstype=$(blkid -o value -s TYPE "${dev}")
     [ -n "${fstype}" ]
 }
 
+last_partition() {
+    cat /sys/class/block/"${1##*/}"/*/partition \
+        | sort -n \
+        | tail -n1
+}
+
+partition_number() {
+    cat /sys/class/block/${1##*/}/partition
+}
+
 relabel_all() {
     selinuxtype=$(. /etc/selinux/config && echo ${SELINUXTYPE})
     find "${tmpdir}" | \
@@ -59,6 +100,29 @@ relabel_all() {
         /etc/selinux/${selinuxtype}/contexts/files/file_contexts
 }
 
+resize_partition() {
+    _disk="${1}"
+    _part="${2}"
+    _lastpart=$(last_partition "${_disk}")
+    if [ "${_part}" -ne "${_lastpart}" ]; then
+        printf 'Cannot resize %s, it is not the last partition on the disk\n' \
+            "${_dev}" \
+            >&2
+        return 1
+    fi
+    _uuid=$(sfdisk --part-uuid "${_disk}" "${_part}") || return $?
+    _type=$(sfdisk --part-type "${_disk}" "${_part}") || return $?
+    _label=$(sfdisk --part-label "${_disk}" "${_part}") || return $?
+    sfdisk --delete "${_disk}" "${_part}" || return $?
+    printf 'type=%s, uuid=%s, name="%s"\n' \
+        "${_type}" \
+        "${_uuid}" \
+        "${_label}" \
+        | sfdisk -N "${_part}" "${_disk}" --force \
+        || return $?
+    partx -u "${_disk}"
+}
+
 setup_etc() {
     dev="$1"