mixer: Add plugin support for mixer_consume/read_event

snd_ctl_event is needed by client to get details of event received.
Introduce mixer_read_event() with plugin support to support this.

include/tinyalsa/mixer.h

@@ -35,7 +35,9 @@
 #ifndef TINYALSA_MIXER_H
 #define TINYALSA_MIXER_H
 
+#include <sys/time.h>
 #include <stddef.h>
+#include <sound/asound.h>
 
 #if defined(__cplusplus)
 extern "C" {
@@ -136,6 +138,8 @@ int mixer_ctl_get_range_min(const struct mixer_ctl *ctl);
 
 int mixer_ctl_get_range_max(const struct mixer_ctl *ctl);
 
+int mixer_read_event(struct mixer *mixer, struct snd_ctl_event *ev);
+
 int mixer_consume_event(struct mixer *mixer);
 #if defined(__cplusplus)
 }  /* extern "C" */

src/mixer.c

@@ -545,15 +545,37 @@ int mixer_wait_event(struct mixer *mixer, int timeout)
  * @returns 0 on success.  -errno on failure.
  * @ingroup libtinyalsa-mixer
  */
-int mixer_consume_event(struct mixer *mixer) {
+int mixer_consume_event(struct mixer *mixer)
+{
     struct snd_ctl_event ev;
-    ssize_t count = read(mixer->fd, &ev, sizeof(ev));
-    // Exporting the actual event would require exposing snd_ctl_event
-    // via the header file, and all associated structs.
-    // The events generally tell you exactly which value changed,
-    // but reading values you're interested isn't hard and simplifies
-    // the interface greatly.
-    return (count >= 0) ? 0 : -errno;
+
+    return mixer_read_event(mixer, &ev);
+}
+
+int mixer_read_event(struct mixer *mixer, struct snd_ctl_event *ev)
+{
+    struct mixer_ctl_group *grp;
+    ssize_t count = 0;
+
+    if (mixer->h_grp) {
+        grp = mixer->h_grp;
+        if (grp->event_cnt) {
+            grp->event_cnt--;
+            count = grp->ops->read_event(grp->data, ev, sizeof(*ev));
+            return (count >= 0) ? 0 : -errno;
+        }
+    }
+#ifdef TINYALSA_USES_PLUGINS
+    if (mixer->v_grp) {
+        grp = mixer->v_grp;
+        if (grp->event_cnt) {
+            grp->event_cnt--;
+            count = grp->ops->read_event(grp->data, ev, sizeof(*ev));
+            return (count >= 0) ? 0 : -errno;
+        }
+    }
+#endif
+    return 0;
 }
 
 static unsigned int mixer_grp_get_count(struct mixer_ctl_group *grp)

src/mixer_hw.c

@@ -82,9 +82,18 @@ static int mixer_hw_ioctl(void *data, unsigned int cmd, ...)
     return ioctl(hw_data->fd, cmd, arg);
 }
 
+static ssize_t mixer_hw_read_event(void *data, struct snd_ctl_event *ev,
+                                   size_t size)
+{
+    struct mixer_hw_data *hw_data = data;
+
+    return read(hw_data->fd, ev, size);
+}
+
 static const struct mixer_ops mixer_hw_ops = {
     .close = mixer_hw_close,
     .ioctl = mixer_hw_ioctl,
+    .read_event = mixer_hw_read_event,
 };
 
 int mixer_hw_open(unsigned int card, void **data,