Add var zram system and preperation for r/w FS overlay system

buildroot-external/rootfs-overlay/etc/fstab

@@ -1,11 +1,3 @@
 # <file system>	<mount pt>	<type>	<options>	<dump>	<pass>
 PARTUUID=9262aee5-2d23-4e09-baac-280591e2e834	/boot	vfat	defaults,noatime	0	0
 PARTUUID=c0932a41-44cf-463b-8152-d43188553ed4	/	ext4	defaults,noatime	0	1
-proc		/proc		proc	defaults	0	0
-devpts		/dev/pts	devpts	defaults,gid=5,mode=620,ptmxmode=0666	0	0
-tmpfs		/dev/shm	tmpfs	mode=0777	0	0
-tmpfs		/tmp		tmpfs	mode=1777	0	0
-tmpfs		/run		tmpfs	mode=0755,nosuid,nodev	0	0
-sysfs		/sys		sysfs	defaults	0	0
-#tmpfs		/var/log	tmpfs	defaults	0	0
-tmpfs		/var/tmp	tmpfs	defaults	0	0

buildroot-external/rootfs-overlay/usr/lib/systemd/system/var.mount

@@ -0,0 +1,16 @@
+[Unit]
+Description=OVOS ZRAM var
+DefaultDependencies=no
+Requires=zram-var.service
+After=zram-var.service
+Before=umount.target
+Conflicts=umount.target
+
+[Mount]
+What=/dev/zram2
+Where=/var
+Type=ext4
+Options=nobarrier
+
+[Install]
+WantedBy=local-fs.target

buildroot-external/rootfs-overlay/usr/lib/systemd/system/zram-var.service

@@ -0,0 +1,15 @@
+[Unit]
+Description=OVOS ZRAM var
+DefaultDependencies=no
+Before=var.mount
+RefuseManualStart=true
+RefuseManualStop=true
+
+[Service]
+Type=oneshot
+ExecStart=/usr/libexec/ovos-zram -t fs -m var -s 32M
+RemainAfterExit=true
+StandardOutput=null
+
+[Install]
+WantedBy=ovos-zram.target

buildroot-external/rootfs-overlay/usr/libexec/ovos-zram

@@ -45,8 +45,10 @@ if [ "$TYPE" = "swap" ]; then
     DEVICE="/dev/zram0"
 elif [ "$MOUNT" = "ramdisk" ]; then
     DEVICE="/dev/zram1"
+elif [ "$MOUNT" = "var" ]; then
+    DEVICE="/dev/zram2"
 #elif [ "$MOUNT" = "tmp" ]; then
-#    DEVICE="/dev/zram2"
+#    DEVICE="/dev/zram3"
 else
     echo "[Error] No device for lookup!"
     exit 1
@@ -69,3 +71,13 @@ fi
 if [ "$TYPE" = "fs" ]; then
     mkfs.ext4 -L "ovos-$MOUNT" -O ^has_journal "$DEVICE"
 fi
+
+# Copy persistent file structures into zram device
+if [ "$MOUNT" = "var" ]; then
+    # Check if this is a first run
+    if [ ! -d /mnt/data/var ]; then
+        mkdir -p /mnt/data/var
+        cp -af /var/* /mnt/data/var/
+    fi
+    cp -af /mnt/data/var/* "$DEVICE"
+fi