oss: add a GstDeviceProvider plugin

Based on Alsa's GstDeviceProvider structure, relies on sndstat
file for OSS device enumeration but uses already existing utils
to query caps and names.

Reviewed and thanks to @slomo

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/4879>

subprojects/gst-plugins-good/sys/oss/gstossaudio.c

@@ -25,6 +25,7 @@
 
 #include "common.h"
 #include "gstossaudioelements.h"
+#include "gstossdeviceprovider.h"
 #include "gstosssink.h"
 #include "gstosssrc.h"
 
@@ -32,6 +33,8 @@
 static gboolean
 plugin_init (GstPlugin * plugin)
 {
+  GST_DEVICE_PROVIDER_REGISTER (ossdeviceprovider, plugin);
+
   GST_ELEMENT_REGISTER (osssrc, plugin);
   GST_ELEMENT_REGISTER (osssink, plugin);
 

subprojects/gst-plugins-good/sys/oss/gstossaudioelement.c

@@ -25,10 +25,14 @@
 
 #include "common.h"
 #include "gstossaudioelements.h"
+#include "gstossdeviceprovider.h"
 
 GST_DEBUG_CATEGORY (oss_debug);
 #define GST_CAT_DEFAULT oss_debug
 
+GST_DEVICE_PROVIDER_REGISTER_DEFINE (ossdeviceprovider, "ossdeviceprovider",
+    GST_RANK_SECONDARY, GST_TYPE_OSS_DEVICE_PROVIDER);
+
 void
 oss_element_init (GstPlugin * plugin)
 {

subprojects/gst-plugins-good/sys/oss/gstossaudioelements.h

@@ -34,6 +34,8 @@ G_GNUC_INTERNAL void oss_element_init (GstPlugin * plugin);
 GST_ELEMENT_REGISTER_DECLARE (osssink);
 GST_ELEMENT_REGISTER_DECLARE (osssrc);
 
+GST_DEVICE_PROVIDER_REGISTER_DECLARE(ossdeviceprovider);
+
 G_END_DECLS
 
 #endif /* __GST_OSS_ELEMENTS_H__ */

subprojects/gst-plugins-good/sys/oss/gstossdeviceprovider.c

@@ -0,0 +1,303 @@
+/* GStreamer
+ * Copyright (C) 2023 Matthieu Volat <matthieu.volat@ensimag.fr>
+ *
+ * ossdeviceprovider.c: OSS device probing and monitoring
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Library General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Library General Public License for more details.
+ *
+ * You should have received a copy of the GNU Library General Public
+ * License along with this library; if not, write to the
+ * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
+ * Boston, MA 02111-1307, USA.
+ */
+
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif
+
+#include "gstossdeviceprovider.h"
+#include "gstosshelper.h"
+#include <glib/gstdio.h>
+#include <gst/gst.h>
+#include <fcntl.h>
+#include <unistd.h>
+
+
+static GstDevice *gst_oss_device_new (const gchar * device_name, GstCaps * caps,
+    const gchar * device, GstOssDeviceType type);
+
+G_DEFINE_TYPE (GstOssDeviceProvider, gst_oss_device_provider,
+    GST_TYPE_DEVICE_PROVIDER);
+
+
+static GstDevice *
+add_device (GstDeviceProvider * provider, GstOssDeviceType type, gint devno)
+{
+  gchar devpath[64];
+  gchar mixpath[64];
+  gint fd;
+  GstCaps *caps;
+  gchar *name;
+  GstDevice *device;
+
+  snprintf (devpath, sizeof (devpath), "/dev/dsp%u", devno);
+  snprintf (mixpath, sizeof (mixpath), "/dev/mixer%u", devno);
+
+  switch (type) {
+    case GST_OSS_DEVICE_TYPE_SOURCE:
+      fd = open (devpath, O_RDONLY);
+      break;
+    case GST_OSS_DEVICE_TYPE_SINK:
+      fd = open (devpath, O_WRONLY);
+      break;
+    default:
+      g_assert_not_reached ();
+      break;
+  }
+  if (fd == -1) {
+    GST_WARNING_OBJECT (provider, "Could open device %s for introspection",
+        devpath);
+    return NULL;
+  }
+  caps = gst_oss_helper_probe_caps (fd);
+  close (fd);
+  name = gst_oss_helper_get_card_name (mixpath);
+
+  device = gst_oss_device_new (name, caps, devpath, type);
+  g_free (name);
+  return device;
+}
+
+static GList *
+gst_oss_device_provider_probe (GstDeviceProvider * provider)
+{
+  FILE *sndstat_handle;
+  gchar *sndstat_line = NULL;
+  size_t sndstat_line_len = 0;
+  gint sndstat_device_section = 0;
+  gint ossdevno;
+  gboolean play, rec;
+  GstDevice *device;
+  GList *list = NULL;
+
+  GST_INFO_OBJECT (provider, "Probing OSS devices");
+  if (((sndstat_handle = fopen ("/dev/sndstat", "r")) == NULL)
+      && ((sndstat_handle = fopen ("/proc/sndstat", "r")) == NULL)
+      && ((sndstat_handle = fopen ("/proc/asound/sndstat", "r")) == NULL)) {
+    /* Cannot evaluate OSS devices without this file */
+    GST_WARNING_OBJECT (provider, "No sndstat file found");
+    goto beach;
+  }
+
+  while (!feof (sndstat_handle)) {
+    if (getline (&sndstat_line, &sndstat_line_len, sndstat_handle) == -1) {
+      break;
+    }
+    g_strstrip (sndstat_line);
+
+    if (!sndstat_device_section) {
+      sndstat_device_section = g_str_equal (sndstat_line, "Audio devices:")
+          || g_str_equal (sndstat_line, "Installed devices:")
+          || g_str_equal (sndstat_line, "Installed devices from userspace:");
+      continue;
+    }
+
+    if ((sscanf (sndstat_line, "pcm%u:", &ossdevno) == 1)
+        || (sscanf (sndstat_line, "%u:", &ossdevno) == 1)) {
+      /* At least on FreeBSD, these keywords can be different if hw.snd.verbose is not 0 */
+      if (strstr (sndstat_line, "(play/rec)") != NULL) {
+        play = rec = TRUE;
+      } else if (strstr (sndstat_line, "(play)") != NULL) {
+        play = TRUE, rec = FALSE;
+      } else if (strstr (sndstat_line, "(rec)") != NULL) {
+        play = FALSE, rec = TRUE;
+      } else {
+        play = rec = FALSE;     /* Or should we assume play/rec? */
+      }
+
+      if (play) {
+        device = add_device (provider, GST_OSS_DEVICE_TYPE_SINK, ossdevno);
+        if (device != NULL) {
+          list = g_list_append (list, device);
+        }
+      }
+      if (rec) {
+        device = add_device (provider, GST_OSS_DEVICE_TYPE_SOURCE, ossdevno);
+        if (device != NULL) {
+          list = g_list_append (list, device);
+        }
+      }
+    }
+  }
+
+  free (sndstat_line);
+  fclose (sndstat_handle);
+
+beach:
+  return list;
+}
+
+
+static void
+gst_oss_device_provider_class_init (GstOssDeviceProviderClass * klass)
+{
+  GstDeviceProviderClass *dm_class = GST_DEVICE_PROVIDER_CLASS (klass);
+
+  dm_class->probe = gst_oss_device_provider_probe;
+
+  gst_device_provider_class_set_static_metadata (dm_class,
+      "OSS Device Provider", "Sink/Source/Audio",
+      "List and provides OSS source and sink devices",
+      "Matthieu Volat <matthieu.volat@ensimag.fr>");
+}
+
+static void
+gst_oss_device_provider_init (GstOssDeviceProvider * self)
+{
+}
+
+/*** GstOssDevice implementation ******/
+enum
+{
+  PROP_DEVICE_PATH = 1,
+};
+
+
+G_DEFINE_TYPE (GstOssDevice, gst_oss_device, GST_TYPE_DEVICE);
+
+static GstElement *
+gst_oss_device_create_element (GstDevice * device, const gchar * name)
+{
+  GstOssDevice *oss_dev = GST_OSS_DEVICE (device);
+  GstElement *elem;
+
+  elem = gst_element_factory_make (oss_dev->element, name);
+  g_object_set (elem, "device", oss_dev->device_path, NULL);
+
+  return elem;
+}
+
+static gboolean
+gst_oss_device_reconfigure_element (GstDevice * device, GstElement * element)
+{
+  GstOssDevice *oss_dev = GST_OSS_DEVICE (device);
+
+  g_object_set (element, "device", oss_dev->device_path, NULL);
+
+  return TRUE;
+}
+
+static void
+gst_oss_device_get_property (GObject * object, guint prop_id,
+    GValue * value, GParamSpec * pspec)
+{
+  GstOssDevice *device;
+
+  device = GST_OSS_DEVICE_CAST (object);
+
+  switch (prop_id) {
+    case PROP_DEVICE_PATH:
+      g_value_set_string (value, device->device_path);
+      break;
+    default:
+      G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
+      break;
+  }
+}
+
+static void
+gst_oss_device_set_property (GObject * object, guint prop_id,
+    const GValue * value, GParamSpec * pspec)
+{
+  GstOssDevice *device;
+
+  device = GST_OSS_DEVICE_CAST (object);
+
+  switch (prop_id) {
+    case PROP_DEVICE_PATH:
+      device->device_path = g_value_dup_string (value);
+      break;
+    default:
+      G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
+      break;
+  }
+}
+
+static void
+gst_oss_device_finalize (GObject * object)
+{
+  GstOssDevice *device = GST_OSS_DEVICE (object);
+
+  g_free (device->device_path);
+
+  G_OBJECT_CLASS (gst_oss_device_parent_class)->finalize (object);
+}
+
+static void
+gst_oss_device_class_init (GstOssDeviceClass * klass)
+{
+  GstDeviceClass *dev_class = GST_DEVICE_CLASS (klass);
+  GObjectClass *object_class = G_OBJECT_CLASS (klass);
+
+  dev_class->create_element = gst_oss_device_create_element;
+  dev_class->reconfigure_element = gst_oss_device_reconfigure_element;
+
+  object_class->get_property = gst_oss_device_get_property;
+  object_class->set_property = gst_oss_device_set_property;
+  object_class->finalize = gst_oss_device_finalize;
+
+  g_object_class_install_property (object_class, PROP_DEVICE_PATH,
+      g_param_spec_string ("device-path", "OSS device path",
+          "The path of the OSS device", "",
+          G_PARAM_STATIC_STRINGS | G_PARAM_READWRITE | G_PARAM_CONSTRUCT_ONLY));
+}
+
+static void
+gst_oss_device_init (GstOssDevice * device)
+{
+}
+
+static GstDevice *
+gst_oss_device_new (const gchar * device_name,
+    GstCaps * caps, const gchar * device_path, GstOssDeviceType type)
+{
+  GstOssDevice *gstdev;
+  const gchar *element = NULL;
+  const gchar *klass = NULL;
+
+  g_return_val_if_fail (device_name, NULL);
+  g_return_val_if_fail (device_path, NULL);
+  g_return_val_if_fail (caps, NULL);
+
+  switch (type) {
+    case GST_OSS_DEVICE_TYPE_SOURCE:
+      element = "osssrc";
+      klass = "Audio/Source";
+      break;
+    case GST_OSS_DEVICE_TYPE_SINK:
+      element = "osssink";
+      klass = "Audio/Sink";
+      break;
+    default:
+      g_assert_not_reached ();
+      break;
+  }
+
+  gstdev = g_object_new (GST_TYPE_OSS_DEVICE,
+      "display-name", device_name, "caps", caps, "device-class", klass,
+      "device-path", device_path, NULL);
+
+  gstdev->element = element;
+
+  gst_caps_unref (caps);
+
+  return GST_DEVICE (gstdev);
+}

subprojects/gst-plugins-good/sys/oss/gstossdeviceprovider.h

@@ -0,0 +1,88 @@
+/* GStreamer
+ * Copyright (C) 2023 Matthieu Volat <mathieu.volat@ensimag.fr>
+ *
+ * ossdeviceprovider.c: OSS device probing and monitoring
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Library General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Library General Public License for more details.
+ *
+ * You should have received a copy of the GNU Library General Public
+ * License along with this library; if not, write to the
+ * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
+ * Boston, MA 02111-1307, USA.
+ */
+
+
+#ifndef __GST_OSS_DEVICE_PROVIDER_H__
+#define __GST_OSS_DEVICE_PROVIDER_H__
+
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif
+
+#include <gst/gst.h>
+
+G_BEGIN_DECLS
+
+typedef struct _GstOssDeviceProvider GstOssDeviceProvider;
+typedef struct _GstOssDeviceProviderClass GstOssDeviceProviderClass;
+
+#define GST_TYPE_OSS_DEVICE_PROVIDER                 (gst_oss_device_provider_get_type())
+#define GST_IS_OSS_DEVICE_PROVIDER(obj)              (G_TYPE_CHECK_INSTANCE_TYPE ((obj), GST_TYPE_OSS_DEVICE_PROVIDER))
+#define GST_IS_OSS_DEVICE_PROVIDER_CLASS(klass)      (G_TYPE_CHECK_CLASS_TYPE ((klass), GST_TYPE_OSS_DEVICE_PROVIDER))
+#define GST_OSS_DEVICE_PROVIDER_GET_CLASS(obj)       (G_TYPE_INSTANCE_GET_CLASS ((obj), GST_TYPE_OSS_DEVICE_PROVIDER, GstOssDeviceProviderClass))
+#define GST_OSS_DEVICE_PROVIDER(obj)                 (G_TYPE_CHECK_INSTANCE_CAST ((obj), GST_TYPE_OSS_DEVICE_PROVIDER, GstOssDeviceProvider))
+#define GST_OSS_DEVICE_PROVIDER_CLASS(klass)         (G_TYPE_CHECK_CLASS_CAST ((klass), GST_TYPE_DEVICE_PROVIDER, GstOssDeviceProviderClass))
+#define GST_OSS_DEVICE_PROVIDER_CAST(obj)            ((GstOssDeviceProvider *)(obj))
+
+struct _GstOssDeviceProvider {
+  GstDeviceProvider         parent;
+};
+
+struct _GstOssDeviceProviderClass {
+  GstDeviceProviderClass    parent_class;
+};
+
+GType        gst_oss_device_provider_get_type (void);
+
+
+typedef struct _GstOssDevice GstOssDevice;
+typedef struct _GstOssDeviceClass GstOssDeviceClass;
+
+#define GST_TYPE_OSS_DEVICE                 (gst_oss_device_get_type())
+#define GST_IS_OSS_DEVICE(obj)              (G_TYPE_CHECK_INSTANCE_TYPE ((obj), GST_TYPE_OSS_DEVICE))
+#define GST_IS_OSS_DEVICE_CLASS(klass)      (G_TYPE_CHECK_CLASS_TYPE ((klass), GST_TYPE_OSS_DEVICE))
+#define GST_OSS_DEVICE_GET_CLASS(obj)       (G_TYPE_INSTANCE_GET_CLASS ((obj), GST_TYPE_OSS_DEVICE, GstOssDeviceClass))
+#define GST_OSS_DEVICE(obj)                 (G_TYPE_CHECK_INSTANCE_CAST ((obj), GST_TYPE_OSS_DEVICE, GstOssDevice))
+#define GST_OSS_DEVICE_CLASS(klass)         (G_TYPE_CHECK_CLASS_CAST ((klass), GST_TYPE_DEVICE, GstOssDeviceClass))
+#define GST_OSS_DEVICE_CAST(obj)            ((GstOssDevice *)(obj))
+
+typedef enum
+{
+  GST_OSS_DEVICE_TYPE_INVALID = 0,
+  GST_OSS_DEVICE_TYPE_SOURCE,
+  GST_OSS_DEVICE_TYPE_SINK
+} GstOssDeviceType;
+
+struct _GstOssDevice {
+  GstDevice         parent;
+
+  gchar            *device_path;
+  const gchar      *element;
+};
+
+struct _GstOssDeviceClass {
+  GstDeviceClass    parent_class;
+};
+
+GType        gst_oss_device_get_type (void);
+
+G_END_DECLS
+#endif /* __GST_OSS_DEVICE_PROVIDER_H__ */

subprojects/gst-plugins-good/sys/oss/meson.build

@@ -26,7 +26,7 @@ endif
 
 if have_oss
   plugins += [library('gstossaudio',
-    'gstossaudio.c', 'gstossaudioelement.c', 'gstosshelper.c', 'gstosssink.c', 'gstosssrc.c',
+    'gstossaudio.c', 'gstossaudioelement.c', 'gstossdeviceprovider.c', 'gstosshelper.c', 'gstosssink.c', 'gstosssrc.c',
     c_args : gst_plugins_good_args,
     include_directories : [configinc, libsinc],
     dependencies : [gstaudio_dep, gstbase_dep],