[PATCH v2] meta/recipes-support: Mount overlay-fs for /etc

["Q. Gylstorff" <Quirin.Gylstorff@siemens.com>]

From: Quirin Gylstorff <quirin.gylstorff@siemens.com>

Add an overlay fs[1] mount for /etc. This overlay allows an image update of
root file-system without overwriting the user settings in /etc. The overlay
mounts during the systemd target `local-fs-pre.target.` Due to this target
the by systemd generated fsck service is not a dependency for the overlay.

[1]: https://www.kernel.org/doc/Documentation/filesystems/overlayfs.txt

Signed-off-by: Quirin Gylstorff <quirin.gylstorff@siemens.com>
---
Changes V2:
- add missing file sdimage-efi-overlay.wks
- fix whitespaces

 doc/user_manual.md                            | 26 ++++++
 meta-isar/conf/machine/qemuamd64.conf         |  4 +-
 .../wic/canned-wks/sdimage-efi-overlay.wks    |  4 +
 .../etc-overlay/etc-overlay_0.1.bb            | 39 +++++++++
 .../etc-overlay/files/etc-hostname.service    | 14 ++++
 .../etc-overlay/files/etc.mount               | 15 ++++
 .../files/overlay-parse-etc.service           | 14 ++++
 .../etc-overlay/files/ovl.mount.tmpl          | 14 ++++
 .../etc-overlay/files/postinst                | 31 +++++++
 meta/recipes-support/etc-overlay/files/postrm | 28 +++++++
 scripts/lib/wic/canned-wks/etc-overlay.inc    |  4 +
 scripts/lib/wic/plugins/source/etc-overlay.py | 84 +++++++++++++++++++
 12 files changed, 276 insertions(+), 1 deletion(-)
 create mode 100644 meta-isar/scripts/lib/wic/canned-wks/sdimage-efi-overlay.wks
 create mode 100644 meta/recipes-support/etc-overlay/etc-overlay_0.1.bb
 create mode 100644 meta/recipes-support/etc-overlay/files/etc-hostname.service
 create mode 100644 meta/recipes-support/etc-overlay/files/etc.mount
 create mode 100644 meta/recipes-support/etc-overlay/files/overlay-parse-etc.service
 create mode 100644 meta/recipes-support/etc-overlay/files/ovl.mount.tmpl
 create mode 100755 meta/recipes-support/etc-overlay/files/postinst
 create mode 100644 meta/recipes-support/etc-overlay/files/postrm
 create mode 100644 scripts/lib/wic/canned-wks/etc-overlay.inc
 create mode 100644 scripts/lib/wic/plugins/source/etc-overlay.py

diff --git a/doc/user_manual.md b/doc/user_manual.md
index d13a74e..5ec7003 100644
--- a/doc/user_manual.md
+++ b/doc/user_manual.md
@@ -901,3 +901,29 @@ And build the corresponding image target:
 ```
 bitbake mc:qemuarm64-buster:isar-image-base
 ```
+## Mount overlay for /etc
+
+### Motivation
+
+If a software update solution updates the complete image, the content of `/etc`
+is also set to new image content. In this case, the user needs to reconfigure
+her system.
+
+### Approach/Solution
+
+A possible solution is to create an additional partition, which superimposes
+`/etc` with an [overlay file-system](https://www.kernel.org/doc/Documentation/filesystems/overlayfs.txt).
+
+### Example
+
+Add the following lines to local.conf:
+```
+IMAGE_TYPE = "wic-img"
+WKS_FILE = "sdimage-efi-overlay"
+IMAGE_INSTALL += "etc-overlay"
+```
+And build the corresponding image target:
+
+```
+bitbake mc:qemuamd64-buster:isar-image-base
+```
diff --git a/meta-isar/conf/machine/qemuamd64.conf b/meta-isar/conf/machine/qemuamd64.conf
index 028b738..d429d96 100644
--- a/meta-isar/conf/machine/qemuamd64.conf
+++ b/meta-isar/conf/machine/qemuamd64.conf
@@ -6,11 +6,13 @@ DISTRO_ARCH ?= "amd64"
 KERNEL_NAME ?= "amd64"
 
 IMAGE_TYPE ?= "wic-img"
-WKS_FILE ?= "sdimage-efi"
+WKS_FILE ?= "sdimage-efi-overlay"
 IMAGER_INSTALL += "${GRUB_BOOTLOADER_INSTALL}"
 
 IMAGE_INSTALL += "sshd-regen-keys"
 
+IMAGE_INSTALL += "etc-overlay"
+
 QEMU_ARCH ?= "x86_64"
 QEMU_MACHINE ?= "q35"
 QEMU_CPU ?= ""
diff --git a/meta-isar/scripts/lib/wic/canned-wks/sdimage-efi-overlay.wks b/meta-isar/scripts/lib/wic/canned-wks/sdimage-efi-overlay.wks
new file mode 100644
index 0000000..96f756f
--- /dev/null
+++ b/meta-isar/scripts/lib/wic/canned-wks/sdimage-efi-overlay.wks
@@ -0,0 +1,4 @@
+# sdimage with etc overlay
+
+include sdimage-efi.wks
+include etc-overlay.inc
diff --git a/meta/recipes-support/etc-overlay/etc-overlay_0.1.bb b/meta/recipes-support/etc-overlay/etc-overlay_0.1.bb
new file mode 100644
index 0000000..cbed71d
--- /dev/null
+++ b/meta/recipes-support/etc-overlay/etc-overlay_0.1.bb
@@ -0,0 +1,39 @@
+# Create a overlay for /etc to freeze a default configuration
+#
+# This software is a part of ISAR.
+# Copyright (c) Siemens AG, 2020
+#
+# SPDX-License-Identifier: MIT
+
+
+DESCRIPTION = "overlay systemd-mount"
+
+DEBIAN_DEPENDS = "systemd"
+
+SRC_URI = "file://postinst \
+           file://postrm \
+           file://etc.mount \
+           file://ovl.mount.tmpl \
+           file://overlay-parse-etc.service \
+           file://etc-hostname.service"
+
+FS_COMMIT_INTERVAL ?= "20"
+
+TEMPLATE_VARS  += "FS_COMMIT_INTERVAL"
+TEMPLATE_FILES += "ovl.mount.tmpl"
+
+inherit dpkg-raw
+
+do_install() {
+    install -m 0755 -d ${D}/ovl
+    touch ${D}/ovl/.keep
+
+    TARGET=${D}/lib/systemd/system
+    install -m 0755 -d ${TARGET}
+    install -m 0644 ${WORKDIR}/etc.mount ${TARGET}/etc.mount
+    install -m 0644 ${WORKDIR}/ovl.mount ${TARGET}/ovl.mount
+    install -m 0644 ${WORKDIR}/overlay-parse-etc.service  ${TARGET}/overlay-parse-etc.service
+    install -m 0644 ${WORKDIR}/etc-hostname.service ${TARGET}/etc-hostname.service
+}
+
+addtask do_install after do_transform_template
diff --git a/meta/recipes-support/etc-overlay/files/etc-hostname.service b/meta/recipes-support/etc-overlay/files/etc-hostname.service
new file mode 100644
index 0000000..2306b9f
--- /dev/null
+++ b/meta/recipes-support/etc-overlay/files/etc-hostname.service
@@ -0,0 +1,14 @@
+[Unit]
+Description=set hostname /etc overlay-aware
+Before=network-pre.target
+Wants=network-pre.target
+Requires=etc.mount
+After=etc.mount
+
+[Service]
+Type=oneshot
+RemainAfterExit=yes
+ExecStart=/bin/hostname --boot --file /etc/hostname
+
+[Install]
+WantedBy=basic.target
diff --git a/meta/recipes-support/etc-overlay/files/etc.mount b/meta/recipes-support/etc-overlay/files/etc.mount
new file mode 100644
index 0000000..59ee0d7
--- /dev/null
+++ b/meta/recipes-support/etc-overlay/files/etc.mount
@@ -0,0 +1,15 @@
+[Unit]
+Description=Overlay-mount /etc
+DefaultDependencies=no
+Before=local-fs-pre.target
+Requires=ovl.mount
+After=ovl.mount
+
+[Mount]
+What=overlay
+Where=/etc
+Type=overlay
+Options=noauto,x-systemd.automount,lowerdir=/etc,upperdir=/ovl/etc,workdir=/ovl/.atomic
+
+[Install]
+WantedBy=local-fs-pre.target
diff --git a/meta/recipes-support/etc-overlay/files/overlay-parse-etc.service b/meta/recipes-support/etc-overlay/files/overlay-parse-etc.service
new file mode 100644
index 0000000..eb5d422
--- /dev/null
+++ b/meta/recipes-support/etc-overlay/files/overlay-parse-etc.service
@@ -0,0 +1,14 @@
+[Unit]
+Description=Reload Configuration from the etc overlay
+DefaultDependencies=no
+Requires=etc.mount
+After=etc.mount
+Before=local-fs-pre.target
+
+[Service]
+Type=oneshot
+RemainAfterExit=yes
+ExecStartPre=!/bin/systemctl daemon-reload
+ExecStart=!/bin/systemctl --no-block isolate multi-user.target
+[Install]
+WantedBy=local-fs-pre.target
diff --git a/meta/recipes-support/etc-overlay/files/ovl.mount.tmpl b/meta/recipes-support/etc-overlay/files/ovl.mount.tmpl
new file mode 100644
index 0000000..3593c55
--- /dev/null
+++ b/meta/recipes-support/etc-overlay/files/ovl.mount.tmpl
@@ -0,0 +1,14 @@
+[Unit]
+Description=Mount /etc overlay backing store
+DefaultDependencies=no
+Before=local-fs-pre.target
+Before=etc.mount
+
+[Mount]
+What=/dev/disk/by-partlabel/etcovl
+Where=/ovl
+Type=ext4
+Options=noatime,nodiratime,data=journal,commit=${FS_COMMIT_INTERVAL},nodelalloc
+
+[Install]
+WantedBy=local-fs-pre.target
diff --git a/meta/recipes-support/etc-overlay/files/postinst b/meta/recipes-support/etc-overlay/files/postinst
new file mode 100755
index 0000000..5b00d9d
--- /dev/null
+++ b/meta/recipes-support/etc-overlay/files/postinst
@@ -0,0 +1,31 @@
+#!/bin/sh
+# postinst script for etc-overlay
+#
+# see: dh_installdeb(1)
+
+set -e
+
+case "$1" in
+    configure)
+        deb-systemd-helper enable etc.mount  || true
+        deb-systemd-helper enable ovl.mount  || true
+        deb-systemd-helper enable overlay-parse-etc.service || true
+        deb-systemd-helper enable systemd-remount-fs.service || true
+        deb-systemd-helper enable etc-hostname.service || true
+    ;;
+
+    abort-upgrade|abort-remove|abort-deconfigure)
+    ;;
+
+    *)
+        echo "postinst called with unknown argument \`$1'" >&2
+        exit 1
+        ;;
+esac
+
+# dh_installdeb will replace this with shell code automatically
+# generated by other debhelper scripts.
+
+#DEBHELPER#
+
+exit 0
diff --git a/meta/recipes-support/etc-overlay/files/postrm b/meta/recipes-support/etc-overlay/files/postrm
new file mode 100644
index 0000000..8e69c4d
--- /dev/null
+++ b/meta/recipes-support/etc-overlay/files/postrm
@@ -0,0 +1,28 @@
+#!/bin/sh
+# postrm script for etc-overlay
+#
+# see: dh_installdeb(1)
+
+set -e
+
+case "$1" in
+    purge|remove|upgrade|failed-upgrade|abort-install|abort-upgrade|disappear)
+        deb-systemd-helper disable etc.mount  || true
+        deb-systemd-helper disable ovl.mount  || true
+        deb-systemd-helper disable overlay-parse-etc.service || true
+        deb-systemd-helper disable systemd-remount-fs.service || true
+        deb-systemd-helper disable etc-hostname.service || true
+     ;;
+
+    *)
+        echo "postrm called with unknown argument \`$1'" >&2
+        exit 1
+    ;;
+esac
+
+# dh_installdeb will replace this with shell code automatically
+# generated by other debhelper scripts.
+
+#DEBHELPER#
+
+exit 0
diff --git a/scripts/lib/wic/canned-wks/etc-overlay.inc b/scripts/lib/wic/canned-wks/etc-overlay.inc
new file mode 100644
index 0000000..2ad4ff4
--- /dev/null
+++ b/scripts/lib/wic/canned-wks/etc-overlay.inc
@@ -0,0 +1,4 @@
+# add a overlay partition to the image
+
+# overlay partition
+part --source etc-overlay --ondisk sda --size 100M --extra-space 128M --overhead-factor 1 --label etcovl --align 1024 --fstype=ext4
diff --git a/scripts/lib/wic/plugins/source/etc-overlay.py b/scripts/lib/wic/plugins/source/etc-overlay.py
new file mode 100644
index 0000000..55189a2
--- /dev/null
+++ b/scripts/lib/wic/plugins/source/etc-overlay.py
@@ -0,0 +1,84 @@
+# ex:ts=4:sw=4:sts=4:et
+# -*- tab-width: 4; c-basic-offset: 4; indent-tabs-mode: nil -*-
+#
+# Copyright (c) 2014, Intel Corporation.
+# Copyright (c) 2018, Siemens AG.
+# All rights reserved.
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License version 2 as
+# published by the Free Software Foundation.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License along
+# with this program; if not, write to the Free Software Foundation, Inc.,
+# 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+#
+# DESCRIPTION
+# This implements the 'etc-overlay' source plugin class for 'wic'
+#
+# AUTHORS
+# Tom Zanussi <tom.zanussi (at] linux.intel.com>
+# Andreas Reichel <andreas.reichel.ext (at] siemens.com>
+# Quirin Gylstorff <quirin.gylstorff [at] siemens.com>
+
+
+import logging
+
+msger = logging.getLogger('wic')
+
+from wic.pluginbase import SourcePlugin
+from wic.utils.misc import exec_cmd,BOOTDD_EXTRA_SPACE
+
+class EtcOverlayPlugin(SourcePlugin):
+    """
+    Create an overlay file system scheme for etc
+    """
+
+    name = 'etc-overlay'
+
+    @classmethod
+    def do_prepare_partition(cls, part, source_params, creator, cr_workdir,
+                             oe_builddir, deploy_dir, kernel_dir,
+                             rootfs_dir, native_sysroot):
+
+        part_rootfs_dir = "%s/disk/%s.%s" % (cr_workdir,
+                                             part.label,
+                                             part.lineno)
+        create_dir_cmd = "install -d %s" % part_rootfs_dir
+        exec_cmd(create_dir_cmd)
+
+        exec_cmd("install -m 0755 -d %s/etc" % part_rootfs_dir)
+        exec_cmd("install -m 0755 -d %s/.atomic" % part_rootfs_dir)
+
+        blocks = 16
+        extra_blocks = part.get_extra_block_count(blocks)
+        if extra_blocks < BOOTDD_EXTRA_SPACE:
+            extra_blocks = BOOTDD_EXTRA_SPACE
+        blocks += extra_blocks
+        blocks = blocks + (16 - (blocks % 16))
+
+        msger.debug("Added %d extra blocks to %s to get to %d total blocks",
+                    extra_blocks, part.mountpoint, blocks)
+
+        # ext4 image, created by mkfs.ext4
+        etcovlimg = "%s/%s.%s.img" % (cr_workdir, part.label, part.lineno)
+        partfs_cmd = "dd if=/dev/zero of=%s bs=512 count=%d" % (etcovlimg,
+                                                                blocks)
+        exec_cmd(partfs_cmd)
+
+        partfs_cmd = "mkfs.ext4 %s -d %s" % (etcovlimg, part_rootfs_dir)
+        exec_cmd(partfs_cmd)
+
+        chmod_cmd = "chmod 644 %s" % etcovlimg
+        exec_cmd(chmod_cmd)
+
+        du_cmd = "du -Lbks %s" % etcovlimg
+        etcovlimg_size = int(exec_cmd(du_cmd).split()[0])
+
+        part.size = etcovlimg_size
+        part.source_file = etcovlimg
-- 
2.20.1