Begin persistent storage implementation

Most of the logic in the `init-storage` script is the same as it was in
Aimee OS v1 (Gentoo).  The major difference is now we are initializing
the data volume in the initramfs instead of in the real OS.  This allows
us to make all of `/etc` writable via OverlayFS, instead of having only
certain sub-directories writable via bind-mounts.

Buildroot doesn't really have any tools for building an initramfs,
unfortunately.  It does have a bit of infrastructure for running
`dracut`, but I'd really rather avoid having that much complexity in the
initramfs; all we need is to run the `init-storage` script and then
switch root.  Instead, the `mkinitramfs.sh` script, called in the
post-build stage, creates the CPIO archive from files in the target
directory.  The only particularly interesting bit is how it resolves
shared library dependencies, to make sure the appropriate resources are
available for the requisite commands.

I briefly considered building a statically-linked BusyBox just for the
initramfs.  Since it doesn't provide several important tools like
`btrfs`/`mkfs.btrfs`, I had to implement the dynamic link resolution
function anyway.  It made sense, then, to copy Dash and the necessary
Coreutils binaries themselves.

Config.in

@@ -15,6 +15,7 @@ config AIMEEOS
 	select BR2_PACKAGE_HOST_MTOOLS
 	select BR2_TARGET_GRUB2
 	select BR2_PACKAGE_HOST_ZSTD
+	select BR2_PACKAGE_AIMEE_OS_UTILS
 	help
 	  Enable all Aimee OS features.
 
@@ -35,3 +36,5 @@ config AIMEEOS_DEFAULT_ROOTFLAGS
 	string "Default kernel command line argumens"
 	help
 	  Additional command line arguments to pass to the kernel by default.
+
+source "$BR2_EXTERNAL_AIMEEOS_PATH/package/aimee-os-utils/Config.in"

boot/grub2/gen-grub-cfg.sh

@@ -9,5 +9,6 @@ cat > "${TARGET_DIR}"/boot/grub.cfg <<EOF
 menuentry "Aimee OS ${vers} (Buildroot ${br2_vers}) on \$dev" --class gnu-linux --id "id-\$partuuid" "\$dev" "\$partuuid" {
     set root="\$2"
     linux "/boot/${kernel_filename}" root=PARTUUID=\$3 ro \$rootflags
+    initrd "/boot/initramfs.img.zst"
 }
 EOF

boot/initramfs/init-storage.sh

@@ -0,0 +1,165 @@
+#!/bin/sh
+# vim: set sw=4 ts=4 sts=4 et :
+
+SUBVOLUMES='
+    /var
+    /var/log
+    /var/tmp
+    /etc
+'
+
+cleanup() {
+    if [ -n "${tmpdir}" ] && [ "${tmpdir}" != / ]; then
+        if mountpoint -q "${tmpdir}"; then
+            umount "${tmpdir}"
+        fi
+        rm -rf "${tmpdir}"
+        unset tmpdir
+    fi
+}
+
+copy_vol() {
+    dev="$1"
+    vol=$2
+
+    printf 'Copying %s contents to data volume\n' "${vol}" >&2
+    mount -o subvol="${vol#/}" "${dev}" "${tmpdir}" || exit
+    cp -au${VERBOSE+v} /sysroot/${vol#/}/. "${tmpdir}" || exit
+    umount "${tmpdir}"
+}
+
+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' "${dev}" >&2
+    mkfs.btrfs --quiet "${dev}" || exit
+
+    mount "${dev}" "${tmpdir}" || exit
+    for vol in ${SUBVOLUMES}; do
+        mkdir -p "${tmpdir}${vol%/*}" || exit
+        btrfs subvolume create "${tmpdir}${vol}" || exit
+    done
+    relabel_all
+    umount "${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() {
+    if [ ! -d /sys/fs/selinux ] || [ ! -f /etc/selinux/config ]; then
+        return
+    fi
+    selinuxtype=$(. /etc/selinux/config && echo ${SELINUXTYPE})
+    find "${tmpdir}" | \
+    setfiles \
+        -v \
+        -F \
+        -m \
+        -r "${tmpdir}" \
+        -s \
+        /etc/selinux/${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}" --quiet --force \
+        || return $?
+    partx -u "${_disk}"
+}
+
+setup_etc() {
+    dev="$1"
+
+    echo 'Initializing /etc overlay' >&2
+    mkdir -p /run/aimeeos/etc || return
+    mount -o subvol=etc "${dev}" /run/aimeeos/etc || return
+    mkdir -p /run/aimeeos/etc/rw /run/aimeeos/etc/work || return
+    mount -t overlay \
+        -o lowerdir=/sysroot/etc,upperdir=/run/aimeeos/etc/rw,workdir=/run/aimeeos/etc/work \
+        overlay \
+        /sysroot/etc
+}
+
+rootdev=$(findfs "$1")
+datapart=$(findfs "${2:-PARTLABEL=aimeeos-data}")
+if [ -b "${datapart}" ]; then
+    printf 'Found data partition: %s\n' "${datapart}" >&2
+else
+    echo 'Could not identify data partition' >&2
+    exit 1
+fi
+
+trap cleanup INT TERM QUIT EXIT
+tmpdir=/run/storinit
+mkdir -p "${tmpdir}"
+
+if ! has_fs "${datapart}"; then
+    format_dev "${datapart}"
+fi
+
+mkdir -p /sysroot
+mount -o ro "${rootdev}" /sysroot || exit
+
+setup_etc "${datapart}"
+copy_vol "${datapart}" /var
+exit 0

boot/initramfs/initramfs-init.sh

@@ -0,0 +1,27 @@
+#!/bin/sh
+
+mkdir -p \
+    /dev \
+    /proc \
+    /run \
+    /sys \
+    /sysroot \
+    && :
+
+mount -t devtmpfs devtmpfs /dev
+mount -t proc proc /proc
+mount -t sysfs sysfs /sys
+mount -t tmpfs tmpfs /run
+
+set -- $(cat /proc/cmdline)
+for arg; do
+    case "${arg}" in
+    root=*)
+        root=${arg#root=}
+        ;;
+    esac
+done
+
+init-storage "${root}"
+
+exec switch_root /sysroot /sbin/init

boot/mkinitramfs.sh

@@ -0,0 +1,113 @@
+#!/bin/sh
+
+if [ $(id -u) != 0 ]; then
+    exec "${HOST_DIR}"/bin/fakeroot "$0" "$@"
+fi
+
+export PATH="${HOST_DIR}:${PATH}"
+
+TARGET_DIR=$1
+WORKDIR=$(mktemp -d)
+OUTDIR="${WORKDIR}"/initramfs
+LIB_CACHE="${WORKDIR}"/libs.cache
+PKGDIR="${0%/*}"
+
+trap 'rm -rf "${WORKDIR}"' INT QUIT TERM EXIT
+
+cache_libs() {
+    find \
+        "${TARGET_DIR}"/usr/lib \
+        "${TARGET_DIR}"/usr/lib64 \
+        \( -type f -o -type l \) \
+        -name '*.so*' \
+        | sed "s@${TARGET_DIR}@@" \
+        > "${LIB_CACHE}"
+}
+
+bin_install() {
+    for arg; do
+        arg=${arg#/}
+        [ -e "${OUTDIR}/${arg}" ] && continue
+        mkdir -p "${OUTDIR}/${arg%/*}"
+        cp -a "${TARGET_DIR}/${arg}" "${OUTDIR}/${arg}"
+        if [ -h "${TARGET_DIR}/${arg}" ]; then
+            bin_install "$(realpath --relative-to "${TARGET_DIR}" "${TARGET_DIR}/${arg}")"
+        elif [ -f "${TARGET_DIR}/${arg}" ]; then
+            readelf --dynamic "${TARGET_DIR}/${arg}" \
+                | awk '$2=="(NEEDED)"{gsub(/\[|\]/,"",$5); print $5}' \
+                | while IFS= read -r lib; do
+                    path="$(grep "${lib}"'$' "${LIB_CACHE}")"
+                    if [ -z "${path}" ]; then
+                        printf 'ERROR could not resolve shared library %s\n' "${lib}" >&2
+                        return 1
+                    fi
+                    bin_install "${path}"
+            done
+        elif [ ! -e "${TARGET_DIR}/${arg}" ]; then
+            printf 'ERROR could not find /%s to copy\n' "${arg}" >&2
+            return 1
+        fi
+    done
+}
+
+mk_skel() {
+    mkdir -p "${OUTDIR}"/dev
+    mknod -m 0622 "${OUTDIR}"/dev/console c 5 1
+
+    mkdir -p \
+        "${OUTDIR}"/usr \
+        "${OUTDIR}"/usr/bin \
+        "${OUTDIR}"/usr/sbin \
+        "${OUTDIR}"/usr/lib
+    ln -s usr/bin "${OUTDIR}"/bin
+    ln -s usr/sbin "${OUTDIR}"/sbin
+    ln -s usr/lib "${OUTDIR}"/lib
+    if [ -h "${TARGET_DIR}"/usr/lib64 ]; then
+        cp -P "${TARGET_DIR}"/usr/lib64 "${OUTDIR}"/usr
+    fi
+    if [ -h "${TARGET_DIR}"/lib64 ]; then
+        cp -P "${TARGET_DIR}"/lib64 "${OUTDIR}"
+    fi
+}
+
+rm -rf "${OUTDIR}"
+
+mk_skel || exit
+cache_libs || exit
+
+bin_install \
+    /bin/cat \
+    /bin/cp \
+    /bin/ls \
+    /bin/mkdir \
+    /bin/mount \
+    /bin/rm \
+    /bin/sh \
+    /bin/sort \
+    /bin/tail \
+    /bin/umount \
+    /usr/bin/btrfs \
+    /usr/bin/mkfs.btrfs \
+    /usr/bin/mountpoint \
+    /usr/bin/readlink \
+    /usr/sbin/blkid \
+    /usr/sbin/findfs \
+    /usr/sbin/partx \
+    /usr/sbin/sfdisk \
+    /usr/sbin/switch_root \
+    || exit
+
+if [ -e "${TARGET_DIR}"/usr/bin/setfiles ]; then
+    bin_install /usr/bin/setfiles || exit
+fi
+
+install "${PKGDIR}"/initramfs/initramfs-init.sh "${OUTDIR}"/init || exit
+install "${PKGDIR}"/initramfs/init-storage.sh "${OUTDIR}"/usr/bin/init-storage || exit
+
+mkdir -p "${TARGET_DIR}"/boot
+
+(cd "${OUTDIR}" && find . -mindepth 1 \
+    | LC_ALL=C sort \
+    | cpio --reproducible --quiet -o -H newc \
+    | zstd \
+) > "${TARGET_DIR}"/boot/initramfs.img.zst

external.mk

@@ -1,3 +1,20 @@
+ifeq ($(AIMEEOS),y)
+
+# Disable the default fstab
+SKELETON_INIT_SYSTEMD_ROOT_RO_OR_RW =
+# Disable the default var.mount
+SKELETON_INIT_SYSTEMD_ROOTFS_PRE_CMD_HOOKS =
+
+# Enable required kernel options for Aimee OS storage
+define AIMEEOS_LINUX_CONFIG_FIXUPS
+$(call KCONFIG_ENABLE_OPT,CONFIG_BTRFS_FS)
+$(call KCONFIG_ENABLE_OPT,CONFIG_BLK_DEV_INITRD)
+endef
+LINUX_KCONFIG_FIXUP_CMDS += $(AIMEEOS_LINUX_CONFIG_FIXUPS)
+
+# Generate the initramfs image after building the target
+BR2_ROOTFS_POST_BUILD_SCRIPT += $(BR2_EXTERNAL_AIMEEOS_PATH)/boot/mkinitramfs.sh
+
 # Overwrite the grub.cfg provided by Buildroot with our own.
 define AIMEEOS_GRUB2_INSTALL_IMAGES_CMDS
 $(foreach tuple, $(GRUB2_TUPLES-y), \
@@ -27,3 +44,7 @@ define AIMEEOS_GEN_GRUB_CFG
 $(BR2_EXTERNAL_AIMEEOS_PATH)/boot/grub2/gen-grub-cfg.sh $(AIMEEOS_KERNEL_FILENAME)
 endef
 LINUX_TARGET_FINALIZE_HOOKS += AIMEEOS_GEN_GRUB_CFG
+
+endif
+
+include $(sort $(wildcard $(BR2_EXTERNAL_AIMEEOS_PATH)/package/*/*.mk))

package/aimee-os-utils/Config.in

@@ -0,0 +1,8 @@
+config BR2_PACKAGE_AIMEE_OS_UTILS
+    bool
+    select BR2_PACKAGE_BTRFS_PROGS
+    select BR2_PACKAGE_UTIL_LINUX
+    select BR2_PACKAGE_UTIL_LINUX_BINARIES
+    select BR2_PACKAGE_UTIL_LINUX_MOUNTPOINT
+    select BR2_PACKAGE_UTIL_LINUX_PARTX
+    select BR2_PACKAGE_UTIL_LINUX_SWITCH_ROOT

package/aimee-os-utils/aimee-os-utils.mk

@@ -0,0 +1,21 @@
+################################################################################
+#
+# Aimee OS Utils
+#
+################################################################################
+
+AIMEE_OS_UTILS_VERSION = 2.0
+AIMEE_OS_UTILS_LICENSE = GPL-3.0+
+AIMEE_OS_UTILS_DEPENDENCIES = \
+	host-fakeroot \
+	btrfs-progs \
+
+AIMEE_OS_UTILS_SOURCE =
+
+define AIMEE_OS_UTILS_INSTALL_INIT_SYSTEMD
+	$(INSTALL) -D -m u=rw,go=r \
+		$(AIMEE_OS_UTILS_PKGDIR)/var.mount \
+		$(TARGET_DIR)/usr/lib/systemd/system/var.mount
+endef
+
+$(eval $(generic-package))

package/aimee-os-utils/var.mount

@@ -0,0 +1,12 @@
+[Unit]
+Description=/var
+DefaultDependencies=no
+Conflicts=umount.target
+Before=local-fs.target umount.target
+After=swap.target
+
+[Mount]
+What=PARTLABEL=aimeeos-data
+Where=/var
+Type=btrfs
+Options=subvol=var,nosuid,nodev,noexec