Allow sync to persistent storage

README.md

@@ -33,6 +33,7 @@ See [raspberrypi/linux@cef3970381](https://github.com/raspberrypi/linux/commit/c
 
 1.  [Install](#install)
     -   [Manually start or stop](#manually-start-or-stop)
+    -   [Sync files to disk](#sync-files-to-disk)
 2.  [Update](#update)
 3.  [Uninstall](#uninstall)
 4.  [Configure](#customize)
@@ -59,6 +60,19 @@ sudo ./zram-config/install.bash
 Use `sudo systemctl {start|stop} zram-config.service` to start or stop zram-config.
 This will ensure that any changes are properly synced to the persistent storage before system poweroff.
 
+#### Sync files to disk
+
+Run `sudo zram-config sync` to sync any changes in the zram filesystems managed by zram-config to persistent storage.
+If you have concerns about losing data due to sudden power loss you could use this to ensure that changes are synced to disk periodically.
+
+A default sync service that will sync files to disk every night can be installed by running the following.
+
+``` shell
+sudo /path/to/zram-config/install.bash sync
+```
+
+Note that this sync service is not installed by default, you must install it separately.
+
 ### Update
 
 ``` shell

install.bash

@@ -6,6 +6,13 @@ if [[ "$(id -u)" -ne 0 ]]; then
   echo "ERROR: You need to be ROOT (sudo can be used)."
   exit 1
 fi
+if [[ $1 == "sync" ]]; then
+  install -m 644 "$BASEDIR"/zsync.* /etc/systemd/system/
+  systemctl daemon-reload
+  systemctl enable --now zsync.timer
+  echo "#####     zsync service is now installed     #####"
+  exit 0
+fi
 if [[ $(systemctl is-active zram-config.service) == "active" ]]; then
   echo -e "ERROR: zram-config service is still running.\\nPlease run \"sudo ${BASEDIR}/update.bash\" to update zram-config instead."
   exit 1

uninstall.bash

@@ -15,6 +15,10 @@ zram-config "stop"
 tar -cf "${BASEDIR}/logs.tar" --directory=/usr/local/share/zram-config log
 systemctl disable zram-config.service
 rm -f /etc/systemd/system/zram-config.service
+if [[ -f /etc/systemd/system/zsync.timer ]]; then
+  systemctl disable zsync.timer
+  rm -f /etc/systemd/system/zsync.*
+fi
 sed -i '\|^ReadWritePaths=/usr/local/share/zram-config/log$|d' /lib/systemd/system/logrotate.service
 systemctl daemon-reload
 rm -f /usr/local/sbin/zram-config

zram-config

@@ -160,6 +160,23 @@ removeZswap() {
 	echo "removeZswap: Device /dev$ZRAM_DEV removed." >> "$ZLOG"
 }
 
+syncZdir() {
+	echo "syncZdir: Beginning sync of device /dev${ZRAM_DEV}." >> "$ZLOG"
+
+	[[ -z $TARGET_DIR ]] && return 1
+	if ! (umount --verbose "${TARGET_DIR}/" >> "$ZLOG" 2>&1); then
+		[[ -x $(command -v lsof) ]] && lsof "${TARGET_DIR}/" >> "$ZLOG" 2>&1
+		umount --verbose --lazy "${TARGET_DIR}/" >> "$ZLOG" 2>&1 || return 1
+	fi
+
+	mergeOverlay >> "$ZLOG" 2>&1 || return 1
+
+	mkdir -p "${ZDIR}${ZRAM_DEV}/upper" "${ZDIR}${ZRAM_DEV}/workdir" "$TARGET_DIR" >> "$ZLOG" 2>&1 || return 1
+	mount --verbose --types overlay -o "redirect_dir=on,lowerdir=${ZDIR}${BIND_DIR},upperdir=${ZDIR}${ZRAM_DEV}/upper,workdir=${ZDIR}${ZRAM_DEV}/workdir" "overlay${ZRAM_DEV//[!0-9]/}" "$TARGET_DIR" >> "$ZLOG" 2>&1 || return 1
+
+	echo "syncZdir: Device /dev$ZRAM_DEV synced." >> "$ZLOG"
+}
+
 serviceConfiguration() {
 	if [[ $1 == "stop" ]]; then
 		echo "Stopping services that interfere with zram device configuration." >> "$ZLOG"
@@ -292,8 +309,42 @@ case "$1" in
 		rm -fv "$TMPDIR"/zram-device-list.rev "$TMPDIR"/zram-device-list >> "$ZLOG"
 		;;
 
+	sync)
+		echo "zram-config sync $(date +%Y-%m-%d-%H:%M:%S)" | tee -a "$ZLOG"
+		tac "$TMPDIR"/zram-device-list > "$TMPDIR"/zram-device-list.rev
+		while read -r line; do
+			case "$line" in
+				"#"*)
+					# Skip comment line
+					continue
+					;;
+
+				"")
+					# Skip empty line
+					continue
+					;;
+
+				*)
+					# shellcheck disable=SC2086
+					set -- $line
+					echo "ztab sync ${1} ${2} ${3} ${4}" >> "$ZLOG"
+					case "$1" in
+						dir|log)
+							ZRAM_DEV="$2"
+							TARGET_DIR="$3"
+							BIND_DIR="$4"
+							[[ -z $SERVICE ]] && serviceConfiguration "stop"
+							syncZdir
+							;;
+					esac
+					;;
+			esac
+		done < "$TMPDIR"/zram-device-list.rev
+		rm -fv "$TMPDIR"/zram-device-list.rev >> "$ZLOG"
+		;;
+
 	*)
-		echo "Usage: zram-config {start|stop}"
+		echo "Usage: zram-config {start|stop|sync}"
 		exit 0
 		;;
 esac

zsync.service

@@ -0,0 +1,8 @@
+[Unit]
+Description=Perform nightly zram sync to persistent storage
+After=zram-config.service
+Wants=zsync.timer
+
+[Service]
+Type=oneshot
+ExecStart=/usr/local/sbin/zram-config "sync" 

zsync.timer

@@ -0,0 +1,11 @@
+[Unit]
+Description=Perform nightly zram sync to persistent storage
+
+[Timer]
+Unit=zsync.service
+OnCalendar=*-*-* 00:55
+RandomizedDelaySec=10m
+Persistent=true
+
+[Install]
+WantedBy=timers.target