document & implement initramfs scripts for ubuntu

Makefile

@@ -2,6 +2,7 @@ PKGNAME ?= grub-btrfs
 PREFIX ?= /usr
 
 INITCPIO ?= false
+MKINITRAMFS ?= false
 SYSTEMD ?= true
 OPENRC ?= false
 
@@ -59,6 +60,11 @@ install:
 		install -Dm644 "initramfs/Arch Linux/overlay_snap_ro-install" "$(LIB_DIR)/initcpio/install/grub-btrfs-overlayfs"; \
 		install -Dm644 "initramfs/Arch Linux/overlay_snap_ro-hook" "$(LIB_DIR)/initcpio/hooks/grub-btrfs-overlayfs"; \
 	 fi
+	@# Ubuntu like distros only :
+	@if test "$(MKINITRAMFS)" = true; then \
+		echo "Installing mkinitramfs hook"; \
+		initramfs/ubuntu/setup install; \
+	 fi
 	@install -Dm644 -t "$(SHARE_DIR)/licenses/$(PKGNAME)/" LICENSE
 	@install -Dm644 -t "$(SHARE_DIR)/doc/$(PKGNAME)/" README.md
 	@install -Dm644 "initramfs/readme.md" "$(SHARE_DIR)/doc/$(PKGNAME)/initramfs-overlayfs.md"
@@ -80,6 +86,7 @@ uninstall:
 	@rm -f "$(DESTDIR)/etc/conf.d/grub-btrfsd;"
 	@rm -f "$(LIB_DIR)/initcpio/install/grub-btrfs-overlayfs"
 	@rm -f "$(LIB_DIR)/initcpio/hooks/grub-btrfs-overlayfs"
+	@initramfs/ubuntu/setup uninstall || true
 	@rm -f "$(MAN_DIR)/man8/grub-btrfs.8.bz2"
 	@rm -f "$(MAN_DIR)/man8/grub-btrfsd.8.bz2"
 	@# Arch Linux UNlike distros only :
@@ -108,14 +115,15 @@ help:
 	@echo "           uninstall"
 	@echo "           help"
 	@echo
-	@echo "  parameter | type | description                    | defaults"
-	@echo "  ----------+------+--------------------------------+----------------------------"
-	@echo "  DESTDIR   | path | install destination            | <unset>"
-	@echo "  PREFIX    | path | system tree prefix             | '/usr'"
-	@echo "  SHARE_DIR | path | shared data location           | '\$$(DESTDIR)\$$(PREFIX)/share'"
-	@echo "  LIB_DIR   | path | system libraries location      | '\$$(DESTDIR)\$$(PREFIX)/lib'"
-	@echo "  PKGNAME   | name | name of the ditributed package | 'grub-btrfs'"
-	@echo "  INITCPIO  | bool | include mkinitcpio hook        | false"
-	@echo "  SYSTEMD   | bool | include unit files             | true"
-	@echo "  OPENRC    | bool | include OpenRc daemon          | false"
+	@echo "  parameter   | type | description                    | defaults"
+	@echo "  ------------+------+--------------------------------+----------------------------"
+	@echo "  DESTDIR     | path | install destination            | <unset>"
+	@echo "  PREFIX      | path | system tree prefix             | '/usr'"
+	@echo "  SHARE_DIR   | path | shared data location           | '\$$(DESTDIR)\$$(PREFIX)/share'"
+	@echo "  LIB_DIR     | path | system libraries location      | '\$$(DESTDIR)\$$(PREFIX)/lib'"
+	@echo "  PKGNAME     | name | name of the ditributed package | 'grub-btrfs'"
+	@echo "  INITCPIO    | bool | include mkinitcpio hook        | false"
+	@echo "  MKINITRAMFS | bool | include mkinitramfs hook       | false"
+	@echo "  SYSTEMD     | bool | include unit files             | true"
+	@echo "  OPENRC      | bool | include OpenRc daemon          | false"
 	@echo

initramfs/readme.md

@@ -44,6 +44,13 @@ Distributions that use Dracut to make their initramfs (many of the Fedora based
 Grub-btrfs provides the variable `GRUB_BTRFS_SNAPSHOT_KERNEL_PARAMETERS` to add any command to the kernel command line. Set it to `GRUB_BTRFS_SNAPSHOT_KERNEL_PARAMETERS="rd.live.overlay.overlayfs=1"` to make snapshots immutable when booted into. 
 After changing this run `sudo /etc/grub.d/41_snapshots-btrfs` to generate a new snapshot-submenu with the parameter added. 
 
+#### Ubuntu
+ Install initramfs scripts & re-generate initramfs.
+
+``` shell
+sudo initramfs/ubuntu/setup install
+```
+
 #### Other distribution
 Refer to your distribution's documentation or contribute to this project to add a paragraph.
 #

initramfs/ubuntu/hooks/grub-btrfs-overlay

@@ -0,0 +1,15 @@
+#!/bin/sh -e
+PREREQ=
+prereqs() {
+	echo "$PREREQ"
+}
+case "$1" in
+	prereqs)
+		prereqs
+		exit 0
+		;;
+esac
+
+. /usr/share/initramfs-tools/hook-functions
+manual_add_modules overlay
+copy_exec /usr/bin/findmnt /usr/bin

initramfs/ubuntu/scripts/local-bottom/grub-btrfs-overlay

@@ -0,0 +1,32 @@
+#!/bin/sh -e
+PREREQ=
+prereqs() {
+	echo "$PREREQ"
+}
+case $1 in
+	prereqs)
+		prereqs
+		exit 0
+		;;
+esac
+
+. /scripts/functions
+on_err() {
+	log_failure_msg 'error setting up overlay'
+}
+trap on_err ERR
+if [ -x /usr/bin/btrfs -a -x /usr/bin/findmnt ] &&
+		 [ "$(findmnt -no FSTYPE -M "$rootmnt")" = btrfs ] &&
+		 [ "$(btrfs property get $rootmnt ro)" != ro=false ]
+then
+	log_begin_msg 'remount read-only subvolume as read-only layer in non-persistent, writable overlay'
+	trap log_end_msg EXIT
+	lower_dir="$(mktemp -dp /)"
+	ram_dir="$(mktemp -dp /)"
+	upper_dir="$ram_dir"/upper
+	work_dir="$ram_dir"/work
+	mount --move "$rootmnt" "$lower_dir"
+	mount -t tmpfs cowspace "$ram_dir"
+	mkdir -p "$upper_dir" "$work_dir"
+	mount -t overlay -o lowerdir="$lower_dir",upperdir="$upper_dir",workdir="$work_dir" rootfs "$rootmnt"
+fi

initramfs/ubuntu/setup

@@ -0,0 +1,70 @@
+#!/usr/bin/env bash
+log() {
+	local CODE=$?
+	echo >&2 "$*"
+	return $CODE
+}
+print-help() {
+	log "\
+usage: ${0##*/} [-h] [--] (install|uninstall)
+Install initramfs scripts for Ubuntu.
+
+# Options
+-h	display this help & exit
+
+# Subcommands
+install	install initramfs scripts
+uninstall	remove initramfs scripts"
+}
+usage-error() {
+	print-help
+	exit 2
+}
+action-install() {
+	local SCRIPT_DIR="$(cd -P -- "$(dirname -- "$BASH_SOURCE")" && pwd)"
+	install {"$SCRIPT_DIR",/etc/initramfs-tools}/hooks/grub-btrfs-overlay
+	install {"$SCRIPT_DIR",/etc/initramfs-tools}/scripts/local-bottom/grub-btrfs-overlay
+}
+action-uninstall() {
+	rm -f /etc/initramfs-tools/{hooks,scripts/local-bottom}/grub-btrfs-overlay
+}
+set -e
+while getopts h OPT
+do case "$OPT" in
+	h)
+		print-help
+		exit
+	;;
+	*)
+		usage-error
+esac done
+shift $(( OPTIND - 1 ))
+OPTIND=1
+ACTION=
+case "$#" in
+	0)
+		log event: a subcommand is required
+		usage-error
+		;;
+	1)
+		case "$1" in
+			install|uninstall)
+				ACTION="action-$1"
+				;;
+			*)
+				log "\
+event: unknown subcommand
+subcommand: $1"
+				usage-error
+		esac
+		;;
+	*)
+		log "\
+event: too many arguments
+arguments: $*"
+		usage-error
+esac
+"$ACTION" || log "\
+event: execution failure
+suggestion: rerun with sudo"
+exec update-initramfs -u