Implement system-update feature

The `system-update` and `install-update` scripts are the same as from
Aimee OS v1, with references to Gentoo replaced, of course.  We need
some additional kernel features in order to mount the firmware partition
and update the GRUB environment file, and of course the `grub-editenv`
tool itself.  We also need `wget` for now, since that's how the tool
downloads the specified update file from the network.

Eventually, `system-update` will be replaced by a much more robust tool,
with package URL discovery, signature verification, etc.  The shell
script will do for now while development is still proceeding rapidly.

update/install-update.sh

@@ -0,0 +1,101 @@
+#!/bin/sh
+# vim: set sw=4 ts=4 sts=4 et :
+
+EFIMOUNT=/boot/efi
+GRUBENV=${EFIMOUNT}/EFI/BOOT/grubenv
+
+die() {
+    rc=$?
+    if [ $rc -eq 0 ]; then
+        rc=1
+    fi
+    error "$@"
+    exit $rc
+}
+
+error() {
+    printf 'ERROR: '
+    info "$@"
+}
+
+get_partuuid() {
+    blkid -o value -s PARTUUID "$1"
+}
+
+info() {
+    if [ $# -eq 1 ]; then
+        echo "$1" >&2
+    elif [ $# -gt 1 ]; then
+        printf "$@" >&2
+    fi
+}
+
+set_default_boot() {
+    _rc=0
+    mkdir -p newroot || return
+    mount -oro "$1" newroot || return
+    _partuuid=$(get_partuuid "$1")
+    _id=id-${_partuuid}
+    printf 'Setting default boot entry to %s\n' "${_id}"
+    grub-editenv "${GRUBENV}" set "default=${_id}" || rc=$?
+    umount newroot
+    return $rc
+}
+
+warn() {
+    printf 'WARNING: '
+    info "$@"
+}
+
+write_firmware() {
+    _rc=0
+    _esp=$(findfs PARTLABEL='EFI System Partition')
+    if [ -z "${_esp}" ]; then
+        error 'Could not identify EFI System Partition'
+        return 1
+    fi
+    if ! mountpoint -q "${EFIMOUNT}"; then
+        mount -o ro "${_esp}" "${EFIMOUNT}" \
+            || warn 'Failed to mount EFI System Partition'
+    fi
+    if [ -f "${GRUBENV}" ]; then
+        info 'Saving current GRUB environment ...'
+        cp "${GRUBENV}" grubenv \
+            || warn 'Failed to save GRUB environment'
+    fi
+    if mountpoint -q "${EFIMOUNT}"; then
+        umount "${EFIMOUNT}" || return
+    fi
+    info 'Writing firmware image to EFI System Partition (%s) ...\n' "${_esp}"
+    dd if=firmware.img of="${_esp}" bs=1M || _rc=$?
+    if [ $_rc -eq 0 ]; then
+        mount -orw "${_esp}" "${EFIMOUNT}" || rc=$?
+    fi
+    if [ $_rc -eq 0 ]; then
+        if [ -f grubenv ]; then
+            printf 'Restoring GRUB environment ...\n'
+            cp grubenv "${GRUBENV}" || _rc=$?
+        fi
+    fi
+    return $_rc
+}
+
+write_rootfs() {
+    printf 'Writing rootfs image to %s ...\n' "$1"
+    dd if=rootfs.squashfs of="$1" bs=1M
+}
+
+rc=0
+newroot="$1"
+
+write_rootfs "${newroot}" || die 'Failed to write new rootfs image to disk'
+write_firmware || die 'Failed to write new firmware image to disk'
+if ! set_default_boot "${newroot}"; then
+    rc=$?
+    error 'Failed to set default boot option'
+fi
+
+if [ $rc -eq 0 ]; then
+    info 'Successfully installed update'
+fi
+exit $rc

update/make-package.sh

@@ -0,0 +1,17 @@
+#!/bin/sh
+# vim: set sw=4 ts=4 sts=4 et :
+
+UPDATE_PACKAGE=update.tar.zstd
+SRCDIR=$(realpath "${0%/*}")
+
+cd "${BINARIES_DIR}"
+printf 'Creating %s/%s\n' "${BINARIES_DIR}" "${UPDATE_PACKAGE}" >&2
+sha256sum firmware.img > digests || exit
+sha256sum rootfs.squashfs >> digests || exit
+cp -u "${SRCDIR}"/install-update.sh install || exit
+tar -c --zstd -f "${UPDATE_PACKAGE}" \
+    digests \
+    firmware.img \
+    rootfs.squashfs \
+    install \
+    || exit