7 files changed, 300 insertions, 0 deletions

diff --git a/COPYING.MIT b/COPYING.MIT
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index 0000000..89de354
--- /dev/null
+++ b/COPYING.MIT
@@ -0,0 +1,17 @@
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in
+all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+THE SOFTWARE.
diff --git a/README.md b/README.md
new file mode 100644
index 0000000..1e44be2
--- /dev/null
+++ b/README.md
@@ -0,0 +1,71 @@
+This README file contains information on the contents of the
+readonly-rootfs-overlay layer.
+
+Please see the corresponding sections below for details.
+
+# Dependencies
+
+This layer depends on:
+
+  URI: git://git.openembedded.org/bitbake
+  branch: master
+
+  URI: git://git.openembedded.org/openembedded-core
+  layers: meta
+  branch: master
+
+
+# Patches
+
+Please submit any patches against the readonly-rootfs-overlay layer via pull
+request.
+
+
+# Table of Contents
+
+  I. Adding the readonly-rootfs-overlay layer to your build
+ II. Read-only root filesystem
+III. Kernel command line parameters
+
+
+## I. Adding the readonly-rootfs-overlay layer to your build
+
+In order to use this layer, you need to make the build system aware of
+it.
+
+Assuming the readonly-rootfs-overlay layer exists at the top-level of your
+yocto build tree, you can add it to the build system by adding the
+location of the readonly-rootfs-overlay layer to bblayers.conf, along with any
+other layers needed. e.g.:
+
+  BBLAYERS ?= " \
+    /path/to/yocto/meta \
+    /path/to/yocto/meta-poky \
+    /path/to/yocto/meta-yocto-bsp \
+    /path/to/yocto/meta-readonly-rootfs-overlay \
+    "
+
+
+## II. Read-only root filesystem
+
+If you use this layer you do *not* need to set `read-only-rootfs` in the
+`IMAGE_FEATURES` or `EXTRA_IMAGE_FEATURES` variable.
+
+## III. Kernel command line parameters
+
+Example:
+
+```
+root=/dev/vda rootfstype=ext4 rootrw=/dev/vdb rootrwfstype=btrfs
+```
+
+`root=` specifies the read-only root filesystem device. (required)
+
+`rootfstype=` if support for the-read only filesystem is not build into the
+kernel, you can specifiy the required module name here.
+
+`rootrw=` specifies the read-write root filesystem device. If this is not
+specified, `tmpfs` is used.
+
+`rootrwfstype=`  if support for the read-write filesystem is not build into the
+kernel, you can specifiy the required module name here.
diff --git a/conf/layer.conf b/conf/layer.conf
new file mode 100644
index 0000000..72f9c36
--- /dev/null
+++ b/conf/layer.conf
@@ -0,0 +1,10 @@
+# We have a conf and classes directory, add to BBPATH
+BBPATH .= ":${LAYERDIR}"
+
+# We have recipes-* directories, add to BBFILES
+BBFILES += "${LAYERDIR}/recipes-*/*/*.bb \
+        ${LAYERDIR}/recipes-*/*/*.bbappend"
+
+BBFILE_COLLECTIONS += "readonly-rootfs-overlay"
+BBFILE_PATTERN_readonly-rootfs-overlay = "^${LAYERDIR}/"
+BBFILE_PRIORITY_readonly-rootfs-overlay = "6"
diff --git a/recipes-core/images/core-image-rorootfs-overlay-initramfs.bb b/recipes-core/images/core-image-rorootfs-overlay-initramfs.bb
new file mode 100644
index 0000000..4c21555
--- /dev/null
+++ b/recipes-core/images/core-image-rorootfs-overlay-initramfs.bb
@@ -0,0 +1,22 @@
+# Simple initramfs image. Mostly used for live images.
+DESCRIPTION = "Small image capable of booting a device. The kernel includes \
+the Minimal RAM-based Initial Root Filesystem (initramfs), mounts the root fs \
+read only and uses a file system overlay for written data."
+
+PACKAGE_INSTALL = "initramfs-readonly-rootfs-overlay ${VIRTUAL-RUNTIME_base-utils} udev base-passwd ${ROOTFS_BOOTSTRAP_INSTALL}"
+
+# Do not pollute the initrd image with rootfs features
+IMAGE_FEATURES = ""
+
+export IMAGE_BASENAME = "core-image-readonly-rootfs-overlay-initramfs"
+IMAGE_LINGUAS = ""
+
+LICENSE = "MIT"
+
+IMAGE_FSTYPES = "${INITRAMFS_FSTYPES}"
+inherit core-image
+
+IMAGE_ROOTFS_SIZE = "8192"
+IMAGE_ROOTFS_EXTRA_SPACE = "0"
+
+BAD_RECOMMENDATIONS += "busybox-syslog"
diff --git a/recipes-core/initrdscripts/files/init-readonly-rootfs-overlay-boot.sh b/recipes-core/initrdscripts/files/init-readonly-rootfs-overlay-boot.sh
new file mode 100644
index 0000000..315da9b
--- /dev/null
+++ b/recipes-core/initrdscripts/files/init-readonly-rootfs-overlay-boot.sh
@@ -0,0 +1,160 @@
+#!/bin/sh
+
+PATH=/sbin:/bin:/usr/sbin:/usr/bin
+
+ROOT_MOUNT="/rootfs"
+MOUNT="/bin/mount"
+UMOUNT="/bin/umount"
+ROOT_RWDEVICE="tmpfs"
+ROOT_ROMOUNT="/rfs/ro"
+ROOT_RWMOUNT="/rfs/rw"
+
+# Copied from initramfs-framework. The core of this script probably should be
+# turned into initramfs-framework modules to reduce duplication.
+udev_daemon() {
+        OPTIONS="/sbin/udev/udevd /sbin/udevd /lib/udev/udevd /lib/systemd/systemd-udevd"
+
+        for o in $OPTIONS; do
+                if [ -x "$o" ]; then
+                        echo $o
+                        return 0
+                fi
+        done
+
+        return 1
+}
+
+_UDEV_DAEMON=`udev_daemon`
+
+early_setup() {
+    mkdir -p /proc
+    mkdir -p /sys
+    $MOUNT -t proc proc /proc
+    $MOUNT -t sysfs sysfs /sys
+    $MOUNT -t devtmpfs none /dev
+
+    # support modular kernel
+    modprobe isofs 2> /dev/null
+
+    mkdir -p /run
+    mkdir -p /var/run
+
+    $_UDEV_DAEMON --daemon
+    udevadm trigger --action=add
+}
+
+read_args() {
+    [ -z "$CMDLINE" ] && CMDLINE=`cat /proc/cmdline`
+    for arg in $CMDLINE; do
+        optarg=`expr "x$arg" : 'x[^=]*=\(.*\)'`
+        case $arg in
+            root=*)
+                ROOT_DEVICE=$optarg ;;
+            rootfstype=*)
+                modprobe $optarg 2> /dev/null ;;
+            rootrw=*)
+                ROOT_RWDEVICE=$optarg ;;
+            rootrwfstype=*)
+                modprobe $optarg 2> /dev/null ;;
+            video=*)
+                video_mode=$arg ;;
+            vga=*)
+                vga_mode=$arg ;;
+            console=*)
+                if [ -z "${console_params}" ]; then
+                    console_params=$arg
+                else
+                    console_params="$console_params $arg"
+                fi ;;
+        esac
+    done
+}
+
+fatal() {
+    echo $1 >$CONSOLE
+    echo >$CONSOLE
+    exec sh
+}
+
+early_setup
+
+[ -z "$CONSOLE" ] && CONSOLE="/dev/console"
+
+read_args
+
+mount_and_boot() {
+    mkdir -p $ROOT_MOUNT $ROOT_ROMOUNT $ROOT_RWMOUNT
+    mknod /dev/loop0 b 7 0 2>/dev/null
+
+    # Mount read-only root filesystem into initramfs rootfs
+    if ! $MOUNT -o ro,noatime,nodiratime $ROOT_DEVICE $ROOT_ROMOUNT ; then
+        fatal "Could not mount read-only rootfs"
+    fi
+
+    # determine which unification filesystem to use
+    union_fs_type=""
+    if grep -w "overlay" /proc/filesystems; then
+        union_fs_type="overlay"
+    elif grep -w "aufs" /proc/filesystems; then
+        union_fs_type="aufs"
+    else
+        union_fs_type=""
+    fi
+
+    # Build mount options for read write root filesystem.
+    # If no read-write device was specified via kernel commandline, use tmpfs.
+    if [ "tmpfs" == $ROOT_RWDEVICE ]; then
+        ROOT_RWMOUNTOPTIONS="-t tmpfs -o rw,noatime,mode=755"
+    else
+        ROOT_RWMOUNTOPTIONS="-o rw,noatime,mode=755"
+    fi
+
+    # Mount read-write filesystem into initram rootfs
+    if ! $MOUNT $ROOT_RWMOUNTOPTIONS $ROOT_RWDEVICE $ROOT_RWMOUNT ; then
+        fatal "Could not mount read-write rootfs"
+    fi
+
+    # Create/Mount overlay root filesystem 
+    case $union_fs_type in
+        "overlay")
+            mkdir -p $ROOT_RWMOUNT/upperdir $ROOT_RWMOUNT/work
+            $MOUNT -t overlay overlay -o "lowerdir=$ROOT_ROMOUNT,upperdir=$ROOT_RWMOUNT/upperdir,workdir=$ROOT_RWMOUNT/work" $ROOT_MOUNT
+            ;;
+        "aufs")
+            $MOUNT -t aufs -o "dirs=$ROOT_RWMOUNT=rw:$ROOT_ROMOUNT=ro" aufs $ROOT_MOUNT
+            ;;
+        "")
+            fatal "No overlay filesystem type available"
+            ;;
+    esac
+
+    # Move read-only and read-write root filesystem into the overlay filesystem
+    mkdir -p $ROOT_MOUNT/$ROOT_ROMOUNT $ROOT_MOUNT/$ROOT_RWMOUNT
+    $MOUNT --move $ROOT_ROMOUNT $ROOT_MOUNT/$ROOT_ROMOUNT
+    $MOUNT --move $ROOT_RWMOUNT $ROOT_MOUNT/$ROOT_RWMOUNT
+
+    # Watches the udev event queue, and exits if all current events are handled
+    udevadm settle --timeout=3 --quiet
+    # Kills the current udev running processes, which survived after
+    # device node creation events were handled, to avoid unexpected behavior
+    killall -9 "${_UDEV_DAEMON##*/}" 2>/dev/null
+
+    # Move the mount points of some filesystems over to
+    # the corresponding directories under the real root filesystem.
+    for dir in `awk '/\/dev.* \/run\/media/{print $2}' /proc/mounts`; do
+        mkdir -p ${ROOT_MOUNT}/media/${dir##*/}
+        $MOUNT -n --move $dir ${ROOT_MOUNT}/media/${dir##*/}
+    done
+    $MOUNT -n --move /proc ${ROOT_MOUNT}/proc
+    $MOUNT -n --move /sys ${ROOT_MOUNT}/sys
+    $MOUNT -n --move /dev ${ROOT_MOUNT}/dev
+
+    cd $ROOT_MOUNT
+
+    # busybox switch_root supports -c option
+    exec switch_root -c /dev/console $ROOT_MOUNT /sbin/init $CMDLINE ||
+        fatal "Couldn't switch_root, dropping to shell"
+}
+
+mount_and_boot
+
diff --git a/recipes-core/initrdscripts/initramfs-readonly-rootfs-overlay_1.0.bb b/recipes-core/initrdscripts/initramfs-readonly-rootfs-overlay_1.0.bb
new file mode 100644
index 0000000..7c2bdf6
--- /dev/null
+++ b/recipes-core/initrdscripts/initramfs-readonly-rootfs-overlay_1.0.bb
@@ -0,0 +1,19 @@
+SUMMARY = "Read only rootfs with overlay init script"
+LICENSE = "MIT"
+LIC_FILES_CHKSUM = "file://${COREBASE}/meta/COPYING.MIT;md5=3da9cfbcb788c80a0384361b4de20420"
+DEPENDS = "virtual/kernel"
+RDEPENDS_${PN} = "udev"
+SRC_URI = "file://init-readonly-rootfs-overlay-boot.sh"
+
+S = "${WORKDIR}"
+
+do_install() {
+        install -m 0755 ${WORKDIR}/init-readonly-rootfs-overlay-boot.sh ${D}/init
+        install -d ${D}/dev
+        mknod -m 622 ${D}/dev/console c 5 1
+}
+
+FILES_${PN} += " /init /dev "
+
+# Due to kernel dependency
+PACKAGE_ARCH = "${MACHINE_ARCH}"
diff --git a/recipes-kernel/linux/linux-yocto_%.bbappend b/recipes-kernel/linux/linux-yocto_%.bbappend
new file mode 100644
index 0000000..cc2bfe6
--- /dev/null
+++ b/recipes-kernel/linux/linux-yocto_%.bbappend
@@ -0,0 +1 @@
+KERNEL_FEATURES_append = " features/overlayfs/overlayfs.scc"