Add initial files to repository (MR 1)

Makefile

+install:
+	install -Dm 755 src/swclock-offset-boot.sh \
+		$(DESTDIR)$(PREFIX)/sbin/swclock-offset-boot
+	install -Dm 755 src/swclock-offset-shutdown.sh \
+		$(DESTDIR)$(PREFIX)/sbin/swclock-offset-shutdown
+
+install_openrc:
+	install -Dm 755 openrc/swclock-offset-boot.initd \
+		$(DESTDIR)/etc/init.d/swclock-offset-boot
+	install -Dm 755 openrc/swclock-offset-shutdown.initd \
+		$(DESTDIR)/etc/init.d/swclock-offset-shutdown

README.md

+# swclock-offset
+Some devices have a working but non-writable real-time clock (RTC).
+This repository contains two shell scripts: One writes the offset between
+'hwclock' and 'swclock' to a file at shutdown, another one reads the
+offset from the file at boot and sets the 'swclock'. This way the system
+time in userspace is kept in present time.
+
+## Build
+The repository contains a simple Makefile. By `make install` the two
+shell scripts get installed to `/sbin`. Adding `PREFIX=/usr` places them
+to `/usr/sbin`. Variable `DESTDIR` allows to change the install path to
+something like `DESTDIR=$pkgdir`.
+
+To install the two OpenRC service files, perform `make install_openrc`.
+They get installed to `/etc/init.d`. Variable `DESTDIR` applies here as
+well, `PREFIX` does not.
+
+## Managing OpenRC services
+After installing the files, OpenRC services need to be set accordingly.
+
+### Replace service hwclock by osclock
+The service "osclock" is a dummy service simply providing "clock".
+This avoids other services that need "clock" to call the service
+"hwclock".
+```
+rc-update -q del hwclock boot
+rc-update -q add osclock boot
+```
+
+### Assign swclock-offset services to runlevels "boot" and "shutdown"
+The service "swclock-offset-boot" needs to run after the sysfs has
+been mounted. As the sysfs is mounted in runlevel sysinit, assigning
+the service to runlevel boot is enough to keep the order.
+```
+rc-update -q add swclock-offset-boot boot
+rc-update -q add swclock-offset-shutdown shutdown
+```
+
+### Update dependency tree cache
+Before installation of the package "swclock-offset", the system time
+might jump back and forth. Because of this, OpenRC can get confused
+whether the cached dependency tree is old or new. To avoid this
+uncertainty, trigger an update of the dependency tree cache.
+```
+rc-update -q --update
+```
+
+### On package removal
+Restore the original state of the services.
+```
+rc-update -q del swclock-offset-boot boot
+rc-update -q del swclock-offset-shutdown shutdown
+
+rc-update -q del osclock boot
+rc-update -q add hwclock boot
+```
+
+## systemd service files
+Files for systemd are not available yet. Basically they should be set
+up in a similar way like the OpenRC service files.
+
+The script `swclock-offset-boot` needs to be executed once during boot,
+after sysfs becomes available (because it reads `/sys/class/rtc/rtc0/since_epoch`)
+and before fsck (because fsck complains if timestamps are inconsistant).
+
+On shutdown, the script `swclock-offset-shutdown` needs to be executed
+once. This needs to be done before the filesystems get unmounted because
+the script writes the offset to the file `/var/cache/swclock-offset/offset-storage`.
+
+Additionally, like on OpenRC, the usual synchronization between hwclock
+and swclock needs to be disabled (likely some other systemd service that
+needs to be disabled).
+
+## Delete cache file and folder on package removal
+Independent of the init system, on package removal the cache file and
+its folder should be removed as a clean-up action. This can be done by
+e.g.:
+
+```
+#!/bin/sh
+
+offset_file="/var/cache/swclock-offset/offset-storage"
+offset_directory="/var/cache/swclock-offset"
+
+if [ -f $offset_file ]; then
+	rm $offset_file
+fi
+
+if [ -d $offset_directory ]; then
+	rmdir $offset_directory
+fi
+```

openrc/swclock-offset-boot.initd

+#!/sbin/openrc-run
+
+# To avoid time inconsistency at filesystems check, the system time
+# shall be set before "fsck".
+
+description="Setting the system time according to an offset file."
+
+depend()
+{
+	before fsck
+}
+
+start()
+{
+	ebegin "Setting system time"
+	/sbin/swclock-offset-boot
+	eend $?
+}
+
+stop()
+{
+	return 0
+}

openrc/swclock-offset-shutdown.initd

+#!/sbin/openrc-run
+
+# A dedicated shutdown service is used to write the offset file instead
+# of using the stop function of the swclock-offset service at boot. This
+# approach is more fail-safe on different installation/deinstallation
+# situations.
+#
+# Because the shutdown services are performed late within the shutdown
+# runlevel, dependencies are needed to execute the script before
+# processes are killed and filesystems are remounted read-only.
+
+description="Writing the offset between system time and RTC to a file."
+
+depend()
+{
+	before killprocs mount-ro
+}
+
+start()
+{
+	ebegin "Saving swclock-offset"
+	/sbin/swclock-offset-shutdown
+	eend $?
+}
+
+stop()
+{
+	return 0
+}

src/swclock-offset-boot.sh

+#!/bin/sh
+
+# SPDX-FileCopyrightText: 2021 Jakob Hauser <jahau@rocketmail.com>
+#
+# SPDX-License-Identifier: GPL-3.0-or-later
+
+# This shell scripts reads the offset from the file and sets the 'swclock'.
+#
+# To keep the offset calculation simple, the epoch timestamp is used.
+#
+# The RTC is read from the sysfs node.
+#
+# To set the system time, command "date" is used. The "@" sign marks an
+# epoch time format. As the "date" command offers no quiet option, the
+# output is written to the null device.
+
+rtc_sys_node="/sys/class/rtc/rtc0/since_epoch"
+offset_file="/var/cache/swclock-offset/offset-storage"
+
+# check presence of rtc sys node
+if [ ! -f $rtc_sys_node ]; then
+	exit 1
+fi
+
+# check presence of offset file
+if [ ! -f $offset_file ]; then
+	exit 2
+fi
+
+# calculate system time
+hwclock_epoch=$(cat $rtc_sys_node)
+offset_epoch=$(cat $offset_file)
+swclock_epoch=$((hwclock_epoch + offset_epoch))
+
+# set system time, dump output
+date --utc --set=@$swclock_epoch > /dev/null

src/swclock-offset-shutdown.sh

+#!/bin/sh
+
+# SPDX-FileCopyrightText: 2021 Jakob Hauser <jahau@rocketmail.com>
+#
+# SPDX-License-Identifier: GPL-3.0-or-later
+
+# This shell scripts writes the offset between 'hwclock' and 'swclock'
+# to a file.
+#
+# To keep the offset calculation simple, the epoch timestamp is used.
+#
+# The system time is read by command "date". The RTC is read from the
+# sysfs node.
+
+rtc_sys_node="/sys/class/rtc/rtc0/since_epoch"
+offset_directory="/var/cache/swclock-offset"
+
+# check presence of rtc sys node
+if [ ! -f $rtc_sys_node ]; then
+	exit 1
+fi
+
+# check presence of offset directory
+if [ ! -d $offset_directory ]; then
+	mkdir -p $offset_directory
+fi
+
+# calculate offset
+swclock_epoch=$(date --utc +%s)
+hwclock_epoch=$(cat $rtc_sys_node)
+offset_epoch=$((swclock_epoch - hwclock_epoch))
+
+# write offset file
+echo $offset_epoch > $offset_directory/offset-storage