Add the ability to reset a mixer group. Report the remaining buffer size from load_from_buf.

apps/systemlib/mixer/mixer.h

@@ -233,6 +233,11 @@ public:
 	 */
 	void				add_mixer(Mixer *mixer);
 
+	/**
+	 * Remove all the mixers from the group.
+	 */
+	void				reset();
+
 	/**
 	 * Adds mixers to the group based on a text description in a buffer.
 	 *
@@ -269,10 +274,11 @@ public:
 	 * R: <geometry> <roll scale> <pitch scale> <yaw scale> <deadband>
 	 *
 	 * @param buf			The mixer configuration buffer.
-	 * @param buflen		The length of the buffer.
+	 * @param buflen		The length of the buffer, updated to reflect
+	 *				bytes as they are consumed.
 	 * @return			Zero on successful load, nonzero otherwise.
 	 */
-	int				load_from_buf(const char *buf, unsigned buflen);
+	int				load_from_buf(const char *buf, unsigned &buflen);
 
 private:
 	Mixer				*_first;	/**< linked list of mixers */

apps/systemlib/mixer/mixer_group.cpp

@@ -64,14 +64,7 @@ MixerGroup::MixerGroup(ControlCallback control_cb, uintptr_t cb_handle) :
 
 MixerGroup::~MixerGroup()
 {
-	Mixer *mixer;
-
-	/* discard sub-mixers */
-	while (_first != nullptr) {
-		mixer = _first;
-		_first = mixer->_next;
-		delete mixer;
-	}
+	reset();
 }
 
 void
@@ -88,6 +81,19 @@ MixerGroup::add_mixer(Mixer *mixer)
 	mixer->_next = nullptr;
 }
 
+void
+MixerGroup::reset()
+{
+	Mixer *mixer;
+
+	/* discard sub-mixers */
+	while (_first != nullptr) {
+		mixer = _first;
+		_first = mixer->_next;
+		delete mixer;
+	}	
+}
+
 unsigned
 MixerGroup::mix(float *outputs, unsigned space)
 {
@@ -114,7 +120,7 @@ MixerGroup::groups_required(uint32_t &groups)
 }
 
 int
-MixerGroup::load_from_buf(const char *buf, unsigned buflen)
+MixerGroup::load_from_buf(const char *buf, unsigned &buflen)
 {
 	int ret = -1;
 	const char *end = buf + buflen;