virtual_oss: Port to base

This patch diverges quite a bit from the current upstream [1] in a few
ways:

1. virtual_oss(8), virtual_bt_speaker(8) and virtual_oss_cmd(8) are
   actually separate programs.
2. Backends (lib/virtual_oss) are built as separate shared libraries and
   we dlopen() them in virtual_oss(8) and virtual_bt_speaker(8) on
   demand.
3. virtual_equalizer(8) and the sndio and bluetooth backends are built
   as ports, because they depend on third-party libraries.
4. Use newer libav API in bluetooth backend (see HAVE_LIBAV ifdefs) to
   address compiler errors.

[1] https://github.com/freebsd/virtual_oss

Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
Reviewed by:	emaste
Differential Revision:	https://reviews.freebsd.org/D52308

libexec/rc/rc.d/Makefile

@@ -75,6 +75,7 @@ CONFS=	DAEMON \
 	ugidfw \
 	var \
 	var_run \
+	virtual_oss \
 	watchdogd
 
 CONFGROUPS+=		DEVD

libexec/rc/rc.d/virtual_oss

@@ -0,0 +1,119 @@
+#!/bin/sh
+
+# PROVIDE: virtual_oss
+# REQUIRE: kld ldconfig
+# BEFORE: LOGIN sndiod
+# KEYWORD: shutdown
+
+. /etc/rc.subr
+
+name="virtual_oss"
+desc="virtual_oss device manager"
+rcvar="${name}_enable"
+
+command="/usr/sbin/${name}"
+command_args="-B"
+
+load_rc_config "$name"
+start_precmd="${name}_precmd"
+start_cmd="${name}_start"
+stop_cmd="${name}_stop"
+status_cmd="${name}_status"
+
+configs=
+pidpath="/var/run/${name}"
+virtual_oss_default_args="\
+	-S \
+	-C 2 \
+	-c 2 \
+	-r 48000 \
+	-b 24 \
+	-s 8ms \
+	-i 8 \
+	-f /dev/dsp \
+	-d dsp \
+	-t vdsp.ctl"
+
+# Set to NO by default. Set it to "YES" to enable virtual_oss.
+: "${virtual_oss_enable:="NO"}"
+
+#  List of configurations to use. Default is "dsp".
+: "${virtual_oss_configs:="dsp"}"
+
+# Default (dsp) virtual_oss config.
+: "${virtual_oss_dsp:="${virtual_oss_default_args}"}"
+
+virtual_oss_pids()
+{
+	pids=$(pgrep -d ' ' ${name})
+	pids=${pids% }
+	printf '%s\n' "${pids}"
+}
+
+virtual_oss_precmd()
+{
+	/usr/bin/install -d -m 0755 -o root "${pidpath}"
+	load_kld cuse
+}
+
+start_instance()
+{
+	config="$1"
+	instance_args=$(eval "echo \$virtual_oss_${config}")
+	if [ -z "${instance_args}" ]; then
+		warn "no such config: ${config}"
+	else
+		startmsg -n "Starting virtual_oss config: ${config}: "
+		${command} \
+			${command_args} \
+			-D "${pidpath}/${config}.pid" \
+			${instance_args}
+		startmsg "done"
+	fi
+}
+
+stop_instance()
+{
+	config="$1"
+	instance_args=$(eval "echo \$virtual_oss_${config}")
+	if [ -z "${instance_args}" ]; then
+		warn "no such config: ${config}"
+	else
+		startmsg -n "Stopping virtual_oss config: ${config}: "
+		kill "$(cat "${pidpath}/${config}.pid")"
+		rm -f "${pidpath}/${config}.pid"
+		startmsg "done"
+	fi
+}
+
+virtual_oss_start()
+{
+	configs="$1"
+	[ -z "${configs}" ] && configs="${virtual_oss_configs}"
+	for config in ${configs}; do
+		start_instance "${config}"
+	done
+}
+
+virtual_oss_stop()
+{
+	configs="$1"
+	[ -z "${configs}" ] && configs="${virtual_oss_configs}"
+	for config in ${configs}; do
+		stop_instance "${config}"
+	done
+}
+
+virtual_oss_status()
+{
+	pids=$(virtual_oss_pids)
+
+	if [ "${pids}" ]; then
+		echo "${name} is running as pid ${pids}."
+	else
+		echo "${name} is not running."
+		return 1
+	fi
+}
+
+run_rc_command "$@"