Merge pull request #93 from bpankajl/mixer_wait_event

Tinyalsa: Add support to poll on alsa control

include/tinyalsa/mixer.h

@@ -90,6 +90,10 @@ struct mixer_ctl *mixer_get_ctl_by_name_and_index(struct mixer *mixer,
                                                   const char *name,
                                                   unsigned int index);
 
+int mixer_subscribe_events(struct mixer *mixer, int subscribe);
+
+int mixer_wait_event(struct mixer *mixer, int timeout);
+
 unsigned int mixer_ctl_get_id(const struct mixer_ctl *ctl);
 
 const char *mixer_ctl_get_name(const struct mixer_ctl *ctl);

src/mixer.c

@@ -36,6 +36,7 @@
 #include <ctype.h>
 #include <limits.h>
 #include <time.h>
+#include <poll.h>
 
 #include <sys/ioctl.h>
 
@@ -302,6 +303,49 @@ unsigned int mixer_get_num_ctls_by_name(const struct mixer *mixer, const char *n
     return count;
 }
 
+/** Subscribes for the mixer events.
+ * @param mixer A mixer handle.
+ * @param subscribe value indicating subscribe or unsubscribe for events
+ * @returns On success, zero.
+ *  On failure, non-zero.
+ * @ingroup libtinyalsa-mixer
+ */
+int mixer_subscribe_events(struct mixer *mixer, int subscribe)
+{
+    if (ioctl(mixer->fd, SNDRV_CTL_IOCTL_SUBSCRIBE_EVENTS, &subscribe) < 0) {
+        return -1;
+    }
+    return 0;
+}
+
+/** Wait for mixer events.
+ * @param mixer A mixer handle.
+ * @param timeout timout value
+ * @returns On success, zero.
+ *  On failure, non-zero.
+ * @ingroup libtinyalsa-mixer
+ */
+int mixer_wait_event(struct mixer *mixer, int timeout)
+{
+    struct pollfd pfd;
+
+    pfd.fd = mixer->fd;
+    pfd.events = POLLIN | POLLOUT | POLLERR | POLLNVAL;
+
+    for (;;) {
+        int err;
+        err = poll(&pfd, 1, timeout);
+        if (err < 0)
+            return -errno;
+        if (!err)
+            return 0;
+        if (pfd.revents & (POLLERR | POLLNVAL))
+            return -EIO;
+        if (pfd.revents & (POLLIN | POLLOUT))
+            return 1;
+    }
+}
+
 /** Gets a mixer control handle, by the mixer control's id.
  * For non-const access, see @ref mixer_get_ctl
  * @param mixer An initialized mixer handle.