virtual_oss: Introduce virtual_oss_default_control_device rc variable

The -t option gives the user the ability to create a control device for
a given virtual_oss(8) instance, so that the instance's configuration
can be manipulated during runtime with virtual_oss_cmd(8). As is
expected, the control device's name is not known, since it is specified
by the user.

This patch introduces a virtual_oss_default_control_device rc variable,
which defaults to "vdsp.ctl". The goal of this is that third-party
programs and scripts can access the control device of the default
virtual_oss(8) configuration without guessing. This is especially useful
for sbin/devd/snd.conf which deals with hot-swapping sound devices using
virtual_oss(8).

Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
Reviewed by:	markj
Differential Revision:	https://reviews.freebsd.org/D55670

1 files changed, 5 insertions, 1 deletions

diff --git a/libexec/rc/rc.d/virtual_oss b/libexec/rc/rc.d/virtual_oss
index d55b51463442..a25abf256f55 100644
--- a/libexec/rc/rc.d/virtual_oss
+++ b/libexec/rc/rc.d/virtual_oss
@@ -25,6 +25,10 @@ required_modules="cuse"
 configs=
 pidpath="/var/run/${name}"
 default_unit=$(sysctl -n hw.snd.default_unit 2> /dev/null)
+
+# Default configuration's control device.
+: "${virtual_oss_default_control_device:="vdsp.ctl"}"
+
 virtual_oss_default_args="\
 	-S \
 	-C 2 \
@@ -35,7 +39,7 @@ virtual_oss_default_args="\
 	-i 8 \
 	-f /dev/dsp${default_unit} \
 	-d dsp \
-	-t vdsp.ctl"
+	-t ${virtual_oss_default_control_device}"
 
 # Set to NO by default. Set it to "YES" to enable virtual_oss.
 : "${virtual_oss_enable:="NO"}"