libexec/rc: Add var_run rc script

Users with a tmpfs /var/run will lose the directory tree state of
/var/run at reboot. This rc script will optionally (by default)
capture the state of the directory structure in /var/run prior to
shutdown and recreate it at system boot.

Alternatively a user can save the state of the /var/run directories
manually using service var_run save and disable the autosaving of
/var/run state using the var_run_autosave variable, for those
paranoid SSD users.

PR:			259585, 259699
Reported by:		freebsd@walstatt-de.de,
Reviewed by:		philip, gbe (previous version)
MFC after:		1 week
Differential Revision:	https://reviews.freebsd.org/D36386

etc/mtree/BSD.var.dist

@@ -46,6 +46,8 @@
         ..
         ipf             mode=0700 tags=package=ipf
         ..
+        mtree
+        ..
         ntp             uname=ntpd gname=ntpd
         ..
         pkg

libexec/rc/rc.conf

@@ -61,6 +61,12 @@ varmfs_flags="-S"	# Extra mount options for the mfs /var
 mfs_type="auto"		# "md", "tmpfs", "auto" to prefer tmpfs with md as fallback
 populate_var="AUTO"	# Set to YES to always (re)populate /var, NO to never
 cleanvar_enable="YES" 	# Clean the /var directory
+var_run_enable="NO" 	# Save/restore /var/run structure at shutdown/reboot
+var_run_autosave="NO" 	# Only restore /var/run structure at shutdown/reboot
+			# The user is expected to issue service var_run save to
+			# manually save the /var/run mtree
+var_run_mtree="/var/db/mtree/BSD.var-run.mtree"
+			# Where to save /var/run mtree
 local_startup="${_localbase}/etc/rc.d" # startup script dirs.
 script_name_sep=" "	# Change if your startup scripts' names contain spaces
 rc_conf_files="/etc/rc.conf /etc/rc.conf.local"

libexec/rc/rc.d/Makefile

@@ -111,6 +111,7 @@ CONFS=	DAEMON \
 	ugidfw \
 	${_utx} \
 	var \
+	var_run \
 	watchdogd
 
 .if ${MK_NIS} != "no"

libexec/rc/rc.d/var_run

@@ -0,0 +1,47 @@
+#!/bin/sh
+
+# PROVIDE: var_run
+# REQUIRE: mountcritlocal
+# BEFORE: cleanvar
+
+. /etc/rc.subr
+
+name=var_run
+rcvar=var_run_enable
+extra_commands="load save"
+start_cmd="_var_run_start"
+load_cmd="_var_run_load"
+save_cmd="_var_run_save"
+stop_cmd="_var_run_stop"
+
+load_rc_config $name
+
+# Set defaults
+: ${var_run_enable:="NO"}
+: ${var_run_mtree:="/var/db/mtree/BSD.var-run.mtree"}
+: ${var_run_autosave:="YES"}
+
+_var_run_load() {
+	test -f ${var_run_mtree} &&
+		mtree -U -i -q -f ${var_run_mtree} -p /var/run > /dev/null
+}
+
+_var_run_save() {
+	if [ ! -d $(dirname ${var_run_mtree}) ]; then
+		mkdir -p ${var_run_mtree}
+	fi
+	mtree -dcbj -p /var/run > ${var_run_mtree}
+}
+
+_var_run_start() {
+	df -ttmpfs /var/run > /dev/null 2>&1 &&
+		_var_run_load
+}
+
+_var_run_stop() {
+	df -ttmpfs /var/run > /dev/null 2>&1 &&
+		checkyesno var_run_autosave &&
+			_var_run_save
+}
+
+run_rc_command "$1"

share/man/man5/rc.conf.5

@@ -463,6 +463,34 @@ is mounted on normal systems.
 Clean the
 .Pa /var
 directory.
+.It Va var_run_enable
+.Pq Vt bool
+Set to "YES" to enable saving of the
+.Pa /var/run
+directory strcucture into an mtree file at shutdown and the reload of the
+.Pa /var/run
+directory structure at boot.
+.It Va var_run_autosave
+.Pq Vt bool
+In some cases it may be undesirable to save
+.Pa /var/run
+at shutdown.
+When set to "NO"
+.Pa /var/run
+is loaded at reboot but not saved at shutdown. Typically in this scenario
+a
+.Pa service
+.Pa var_run
+.Pa save
+would be performed to save a copy of the
+.Pa /var/run
+directory structure once, to be reload during all subsequent reboots.
+.It Va var_run_mtree
+.Pq Vt str
+Where to save the
+.Pa /var/run
+mtree. The default location is
+.Pa /var/db/mtree/BSD.var-run.mtree .
 .It Va local_startup
 .Pq Vt str
 List of directories to search for startup script files.