alsa: Add udev support

Instead of polling for new devices once per second ask
udev to send us events. Avoids waking up the CPU all the
time and wasting power.

We keep the timeout source as a fallback when udev
support is not enabled, or the udev setup fails for
whatever reason.

The logic for udev_event_ok() was snooped from pulseaudio.

2 files changed, 133 insertions, 5 deletions

diff --git a/backends/alsa/Makefile.am b/backends/alsa/Makefile.am
index 06e04a7..798ce8b 100644
--- a/backends/alsa/Makefile.am
+++ b/backends/alsa/Makefile.am
@@ -8,6 +8,7 @@ AM_CPPFLAGS =							\
 	-I$(top_srcdir)						\
 	-DG_LOG_DOMAIN=\"libmatemixer-alsa\"			\
 	$(GLIB_CFLAGS)						\
+	$(UDEV_CFLAGS)						\
 	$(ALSA_CFLAGS)						\
 	$(NULL)
 
@@ -43,6 +44,7 @@ libmatemixer_alsa_la_SOURCES =                                  \
 
 libmatemixer_alsa_la_LIBADD =                                   \
 	$(GLIB_LIBS)                                            \
+	$(UDEV_LIBS)						\
 	$(ALSA_LIBS)
 
 libmatemixer_alsa_la_LDFLAGS =                                  \
diff --git a/backends/alsa/alsa-backend.c b/backends/alsa/alsa-backend.c
index 39f67cc..2475385 100644
--- a/backends/alsa/alsa-backend.c
+++ b/backends/alsa/alsa-backend.c
@@ -15,9 +15,15 @@
  * License along with this library; if not, see <http://www.gnu.org/licenses/>.
  */
 
+#include "config.h"
+
 #include <glib.h>
 #include <glib-object.h>
 #include <alsa/asoundlib.h>
+#ifdef HAVE_UDEV
+#include <libudev.h>
+#include <glib-unix.h>
+#endif
 
 #include <libmatemixer/matemixer.h>
 #include <libmatemixer/matemixer-private.h>
@@ -45,6 +51,15 @@ struct _AlsaBackendPrivate
     GList      *streams;
     GList      *devices;
     GHashTable *devices_ids;
+
+#ifdef HAVE_UDEV
+    struct {
+        struct udev         *udev;
+        struct udev_monitor *monitor;
+        guint                fd_source;
+        int                  fd;
+    } udev;
+#endif
 };
 
 static void alsa_backend_dispose        (GObject          *object);
@@ -169,15 +184,99 @@ alsa_backend_finalize (GObject *object)
     G_OBJECT_CLASS (alsa_backend_parent_class)->finalize (object);
 }
 
+#ifdef HAVE_UDEV
+static gboolean udev_event_ok (struct udev_device *dev)
+{
+    const char *action = udev_device_get_action (dev);
+
+    if (action && !strcmp (action, "remove"))
+        return TRUE;
+
+    /*
+     * See /lib/udev/rules.d/78-sound-card.rules
+     * why "add" events are not handled here.
+     */
+    if ((!action || !strcmp (action, "change")) &&
+        udev_device_get_property_value (dev, "SOUND_INITIALIZED"))
+        return TRUE;
+
+    return FALSE;
+}
+
 static gboolean
-alsa_backend_open (MateMixerBackend *backend)
+udev_monitor_cb (gint fd,
+                 GIOCondition condition,
+                 gpointer user_data)
 {
-    AlsaBackend *alsa;
+    AlsaBackend *alsa = user_data;
+    struct udev_device *dev;
 
-    g_return_val_if_fail (ALSA_IS_BACKEND (backend), FALSE);
+    dev = udev_monitor_receive_device (alsa->priv->udev.monitor);
+    if (!dev)
+        return TRUE;
 
-    alsa = ALSA_BACKEND (backend);
+    if (!udev_event_ok (dev)) {
+        udev_device_unref (dev);
+        return TRUE;
+    }
+
+    read_devices (alsa);
+
+    udev_device_unref (dev);
+
+    return TRUE;
+}
+
+static gboolean
+udev_monitor_setup (AlsaBackend *alsa)
+{
+    alsa->priv->udev.udev = udev_new ();
+    if (!alsa->priv->udev.udev)
+        return FALSE;
+
+    alsa->priv->udev.monitor = udev_monitor_new_from_netlink (alsa->priv->udev.udev, "udev");
+    if (!alsa->priv->udev.monitor) {
+        udev_unref (alsa->priv->udev.udev);
+        alsa->priv->udev.udev = NULL;
+        return FALSE;
+    }
+
+    if (udev_monitor_filter_add_match_subsystem_devtype (alsa->priv->udev.monitor, "sound", NULL) < 0 ||
+        udev_monitor_enable_receiving (alsa->priv->udev.monitor) < 0) {
+        udev_monitor_unref (alsa->priv->udev.monitor);
+        udev_unref (alsa->priv->udev.udev);
+        alsa->priv->udev.udev = NULL;
+        return FALSE;
+    }
+
+    alsa->priv->udev.fd = udev_monitor_get_fd (alsa->priv->udev.monitor);
+    if (alsa->priv->udev.fd < 0) {
+        udev_monitor_unref (alsa->priv->udev.monitor);
+        udev_unref (alsa->priv->udev.udev);
+        alsa->priv->udev.udev = NULL;
+        return FALSE;
+    }
 
+    alsa->priv->udev.fd_source = g_unix_fd_add (alsa->priv->udev.fd, G_IO_IN, udev_monitor_cb, alsa);
+
+    return TRUE;
+}
+
+static void
+udev_monitor_cleanup (AlsaBackend *alsa)
+{
+    if (!alsa->priv->udev.udev)
+        return;
+
+    g_source_remove (alsa->priv->udev.fd_source);
+    udev_monitor_unref (alsa->priv->udev.monitor);
+    udev_unref (alsa->priv->udev.udev);
+}
+#endif
+
+static void
+timeout_source_setup (AlsaBackend *alsa)
+{
     /* Poll ALSA for changes every second, this only discovers added or removed
      * sound cards, sound card related events are handled by AlsaDevices */
     alsa->priv->timeout_source = g_timeout_source_new_seconds (1);
@@ -187,6 +286,30 @@ alsa_backend_open (MateMixerBackend *backend)
                            NULL);
     g_source_attach (alsa->priv->timeout_source,
                      g_main_context_get_thread_default ());
+}
+
+static void
+timeout_source_cleanup (AlsaBackend *alsa)
+{
+    if (!alsa->priv->timeout_source)
+        return;
+
+    g_source_destroy (alsa->priv->timeout_source);
+}
+
+static gboolean
+alsa_backend_open (MateMixerBackend *backend)
+{
+    AlsaBackend *alsa;
+
+    g_return_val_if_fail (ALSA_IS_BACKEND (backend), FALSE);
+
+    alsa = ALSA_BACKEND (backend);
+
+#ifdef HAVE_UDEV
+    if (!udev_monitor_setup (alsa))
+#endif
+        timeout_source_setup (alsa);
 
     /* Read the initial list of devices so we have some starting point, there
      * isn't really a way to detect errors here, failing to add a device may
@@ -206,7 +329,10 @@ alsa_backend_close (MateMixerBackend *backend)
 
     alsa = ALSA_BACKEND (backend);
 
-    g_source_destroy (alsa->priv->timeout_source);
+    timeout_source_cleanup (alsa);
+#ifdef HAVE_UDEV
+    udev_monitor_cleanup (alsa);
+#endif
 
     if (alsa->priv->devices != NULL) {
         g_list_free_full (alsa->priv->devices, g_object_unref);