proper dbus device reservation

4 files changed, 925 insertions, 1 deletions

diff --git a/libs/ardouralsautil/ardouralsautil/reserve.h b/libs/ardouralsautil/ardouralsautil/reserve.h
new file mode 100644
index 0000000000..6527bd7faa
--- /dev/null
+++ b/libs/ardouralsautil/ardouralsautil/reserve.h
@@ -0,0 +1,88 @@
+/*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: t -*-*/
+
+#ifndef fooreservehfoo
+#define fooreservehfoo
+
+/***
+  Copyright 2009 Lennart Poettering
+
+  Permission is hereby granted, free of charge, to any person
+  obtaining a copy of this software and associated documentation files
+  (the "Software"), to deal in the Software without restriction,
+  including without limitation the rights to use, copy, modify, merge,
+  publish, distribute, sublicense, and/or sell copies of the Software,
+  and to permit persons to whom the Software is furnished to do so,
+  subject to the following conditions:
+
+  The above copyright notice and this permission notice shall be
+  included in all copies or substantial portions of the Software.
+
+  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+  EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+  MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+  NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
+  BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
+  ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+  CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+  SOFTWARE.
+***/
+
+#include <dbus/dbus.h>
+#include <inttypes.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+typedef struct rd_device rd_device;
+
+/* Prototype for a function that is called whenever someone else wants
+ * your application to release the device it has locked. A return
+ * value <= 0 denies the request, a positive return value agrees to
+ * it. Before returning your application should close the device in
+ * question completely to make sure the new application may access
+ * it. */
+typedef int (*rd_request_cb_t)(
+	rd_device *d,
+	int forced);                  /* Non-zero if an application forcibly took the lock away without asking. If this is the case then the return value of this call is ignored. */
+
+/* Try to lock the device. Returns 0 on success, a negative errno
+ * style return value on error. The DBus error might be set as well if
+ * the error was caused D-Bus. */
+int rd_acquire(
+	rd_device **d,                /* On success a pointer to the newly allocated rd_device object will be filled in here */
+	DBusConnection *connection,   /* Session bus (when D-Bus learns about user busses we should switch to user busses) */
+	const char *device_name,      /* The device to lock, e.g. "Audio0" */
+	const char *application_name, /* A human readable name of the application, e.g. "PulseAudio Sound Server" */
+	int32_t priority,             /* The priority for this application. If unsure use 0 */
+	rd_request_cb_t request_cb,   /* Will be called whenever someone requests that this device shall be released. May be NULL if priority is INT32_MAX */
+	DBusError *error);            /* If we fail due to a D-Bus related issue the error will be filled in here. May be NULL. */
+
+/* Unlock (if needed) and destroy an rd_device object again */
+void rd_release(rd_device *d);
+
+/* Set the application device name for an rd_device object. Returns 0
+ * on success, a negative errno style return value on error. */
+int rd_set_application_device_name(rd_device *d, const char *name);
+
+/* Attach a userdata pointer to an rd_device */
+void rd_set_userdata(rd_device *d, void *userdata);
+
+/* Query the userdata pointer from an rd_device. Returns NULL if no
+ * userdata was set. */
+void* rd_get_userdata(rd_device *d);
+
+/* Helper function to get the unique connection name owning a given
+ * name. Returns 0 on success, a negative errno style return value on
+ * error. */
+int rd_dbus_get_name_owner(
+	DBusConnection *connection,
+	const char *name,
+	char **name_owner,
+	DBusError *error);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif
diff --git a/libs/ardouralsautil/request_device.c b/libs/ardouralsautil/request_device.c
new file mode 100644
index 0000000000..9e929c3cd0
--- /dev/null
+++ b/libs/ardouralsautil/request_device.c
@@ -0,0 +1,139 @@
+/*
+ * Copyright (C) 2014 Robin Gareus <robin@gareus.org>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program 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 General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <signal.h>
+#include <string.h>
+#include <fcntl.h>
+#include <errno.h>
+
+#include "ardouralsautil/reserve.h"
+
+static int run = 1;
+
+static void wearedone(int sig) {
+	(void) sig; // skip 'unused variable' compiler warning;
+	fprintf(stderr, "caught signal - shutting down.\n");
+	run=0;
+}
+
+static int stdin_available(void) {
+	errno = 0;
+	if (fcntl(STDIN_FILENO, F_GETFD) == 1) return 0;
+	return errno != EBADF;
+}
+
+static void usage(int status) {
+	printf ("ardour-request-device - DBus Audio Reservation Utility.\n");
+	printf ("Usage: ardour-request-device [ OPTIONS ] <Audio-Device-ID>\n");
+	printf ("Options:\n\
+      -h, --help                 display this help and exit\n\
+      -V, --version              print version information and exit\n\
+");
+
+	printf ("\n\
+This tool issues a dbus request to reserve an ALSA Audio-device.\n\
+If successful other users of the device (e.g. pulseaudio) will\n\
+release the device so that ardour can access it.\n\
+\n\
+ardour-request-device announces itself as \"Ardour ALSA Backend\" and uses the\n\
+maximum possible priority for requesting the device.\n\
+\n\
+The audio-device-id is a string e.g. 'Audio1'\n\
+\n\
+Examples:\n\
+ardour-request-device Audio0\n\
+\n");
+
+	printf ("Report bugs to Robin Gareus <robin@gareus.org>\n");
+	exit (status);
+}
+
+static void print_version(void) {
+	printf ("ardour-request-device 0.1\n\n");
+	printf (
+			"Copyright (C) 2014 Robin Gareus <robin@gareus.org>\n"
+			"This is free software; see the source for copying conditions.  There is NO\n"
+			"warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.\n\n"
+			);
+	exit (0);
+}
+
+int main(int argc, char **argv) {
+	DBusConnection* dbus_connection = NULL;
+	rd_device * reserved_device = NULL;
+	DBusError error;
+	int ret;
+
+	if (argc < 2 || argc > 2) {
+		usage(EXIT_FAILURE);
+	}
+	if (!strcmp(argv[1], "-V") || !strcmp(argv[1], "--version")) {
+		print_version();
+	}
+	if (!strcmp(argv[1], "-h") || !strcmp(argv[1], "--help")) {
+		usage(EXIT_SUCCESS);
+	}
+
+	const char *device_name = argv[1];
+
+	dbus_error_init(&error);
+
+	if (!(dbus_connection = dbus_bus_get (DBUS_BUS_SESSION, &error))) {
+		fprintf(stderr, "Failed to connect to session bus for device reservation: %s\n", error.message ? error.message : "unknown error.");
+		dbus_error_free(&error);
+		return EXIT_FAILURE;
+	}
+
+	if ((ret = rd_acquire (
+					&reserved_device,
+					dbus_connection,
+					device_name,
+					"Ardour ALSA Backend",
+					INT32_MAX,
+					NULL,
+					&error)) < 0)
+	{
+		fprintf(stderr, "Failed to acquire device: '%s'\n%s\n", device_name, (error.message ? error.message : strerror(-ret)));
+		dbus_error_free(&error);
+		dbus_connection_unref(dbus_connection);
+		return EXIT_FAILURE;
+	}
+
+	fprintf(stdout, "Acquired audio-card '%s'\n", device_name);
+	fprintf(stdout, "Press Ctrl+C or close stdin to release the device.\n");
+	fflush(stdout);
+
+	signal(SIGTERM, wearedone);
+	signal(SIGINT, wearedone);
+
+	while (run && dbus_connection_read_write_dispatch (dbus_connection, 200)) {
+		if (!stdin_available()) {
+			fprintf(stderr, "stdin closed - shutting down.\n");
+			break;
+		}
+	}
+
+	rd_release (reserved_device);
+	fprintf(stdout, "Released audio-card '%s'\n", device_name);
+	dbus_error_free(&error);
+	dbus_connection_unref(dbus_connection);
+	return EXIT_SUCCESS;
+}
diff --git a/libs/ardouralsautil/reserve.c b/libs/ardouralsautil/reserve.c
new file mode 100644
index 0000000000..9076333f77
--- /dev/null
+++ b/libs/ardouralsautil/reserve.c
@@ -0,0 +1,681 @@
+/*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: t -*-*/
+
+/***
+  Copyright 2009 Lennart Poettering
+
+  Permission is hereby granted, free of charge, to any person
+  obtaining a copy of this software and associated documentation files
+  (the "Software"), to deal in the Software without restriction,
+  including without limitation the rights to use, copy, modify, merge,
+  publish, distribute, sublicense, and/or sell copies of the Software,
+  and to permit persons to whom the Software is furnished to do so,
+  subject to the following conditions:
+
+  The above copyright notice and this permission notice shall be
+  included in all copies or substantial portions of the Software.
+
+  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+  EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+  MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+  NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
+  BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
+  ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+  CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+  SOFTWARE.
+***/
+
+#include <string.h>
+#include <unistd.h>
+#include <errno.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <assert.h>
+
+#include "ardouralsautil/reserve.h"
+
+struct rd_device {
+	int ref;
+
+	char *device_name;
+	char *application_name;
+	char *application_device_name;
+	char *service_name;
+	char *object_path;
+	int32_t priority;
+
+	DBusConnection *connection;
+
+	unsigned owning:1;
+	unsigned registered:1;
+	unsigned filtering:1;
+	unsigned gave_up:1;
+
+	rd_request_cb_t request_cb;
+	void *userdata;
+};
+
+#define SERVICE_PREFIX "org.freedesktop.ReserveDevice1."
+#define OBJECT_PREFIX "/org/freedesktop/ReserveDevice1/"
+
+static const char introspection[] =
+	DBUS_INTROSPECT_1_0_XML_DOCTYPE_DECL_NODE
+	"<node>"
+	" <!-- If you are looking for documentation make sure to check out\n"
+	"      http://git.0pointer.de/?p=reserve.git;a=blob;f=reserve.txt -->\n"
+	" <interface name=\"org.freedesktop.ReserveDevice1\">"
+	"  <method name=\"RequestRelease\">"
+	"   <arg name=\"priority\" type=\"i\" direction=\"in\"/>"
+	"   <arg name=\"result\" type=\"b\" direction=\"out\"/>"
+	"  </method>"
+	"  <property name=\"Priority\" type=\"i\" access=\"read\"/>"
+	"  <property name=\"ApplicationName\" type=\"s\" access=\"read\"/>"
+	"  <property name=\"ApplicationDeviceName\" type=\"s\" access=\"read\"/>"
+	" </interface>"
+	" <interface name=\"org.freedesktop.DBus.Properties\">"
+	"  <method name=\"Get\">"
+	"   <arg name=\"interface\" direction=\"in\" type=\"s\"/>"
+	"   <arg name=\"property\" direction=\"in\" type=\"s\"/>"
+	"   <arg name=\"value\" direction=\"out\" type=\"v\"/>"
+	"  </method>"
+	" </interface>"
+	" <interface name=\"org.freedesktop.DBus.Introspectable\">"
+	"  <method name=\"Introspect\">"
+	"   <arg name=\"data\" type=\"s\" direction=\"out\"/>"
+	"  </method>"
+	" </interface>"
+	"</node>";
+
+static dbus_bool_t add_variant(
+	DBusMessage *m,
+	int type,
+	const void *data) {
+
+	DBusMessageIter iter, sub;
+	char t[2];
+
+	t[0] = (char) type;
+	t[1] = 0;
+
+	dbus_message_iter_init_append(m, &iter);
+
+	if (!dbus_message_iter_open_container(&iter, DBUS_TYPE_VARIANT, t, &sub))
+		return FALSE;
+
+	if (!dbus_message_iter_append_basic(&sub, type, data))
+		return FALSE;
+
+	if (!dbus_message_iter_close_container(&iter, &sub))
+		return FALSE;
+
+	return TRUE;
+}
+
+static DBusHandlerResult object_handler(
+	DBusConnection *c,
+	DBusMessage *m,
+	void *userdata) {
+
+	rd_device *d;
+	DBusError error;
+	DBusMessage *reply = NULL;
+
+	dbus_error_init(&error);
+
+	d = userdata;
+	assert(d->ref >= 1);
+
+	if (dbus_message_is_method_call(
+		    m,
+		    "org.freedesktop.ReserveDevice1",
+		    "RequestRelease")) {
+
+		int32_t priority;
+		dbus_bool_t ret;
+
+		if (!dbus_message_get_args(
+			    m,
+			    &error,
+			    DBUS_TYPE_INT32, &priority,
+			    DBUS_TYPE_INVALID))
+			goto invalid;
+
+		ret = FALSE;
+
+		if (priority > d->priority && d->request_cb) {
+			d->ref++;
+
+			if (d->request_cb(d, 0) > 0) {
+				ret = TRUE;
+				d->gave_up = 1;
+			}
+
+			rd_release(d);
+		}
+
+		if (!(reply = dbus_message_new_method_return(m)))
+			goto oom;
+
+		if (!dbus_message_append_args(
+			    reply,
+			    DBUS_TYPE_BOOLEAN, &ret,
+			    DBUS_TYPE_INVALID))
+			goto oom;
+
+		if (!dbus_connection_send(c, reply, NULL))
+			goto oom;
+
+		dbus_message_unref(reply);
+
+		return DBUS_HANDLER_RESULT_HANDLED;
+
+	} else if (dbus_message_is_method_call(
+			   m,
+			   "org.freedesktop.DBus.Properties",
+			   "Get")) {
+
+		const char *interface, *property;
+
+		if (!dbus_message_get_args(
+			    m,
+			    &error,
+			    DBUS_TYPE_STRING, &interface,
+			    DBUS_TYPE_STRING, &property,
+			    DBUS_TYPE_INVALID))
+			goto invalid;
+
+		if (strcmp(interface, "org.freedesktop.ReserveDevice1") == 0) {
+			const char *empty = "";
+
+			if (strcmp(property, "ApplicationName") == 0 && d->application_name) {
+				if (!(reply = dbus_message_new_method_return(m)))
+					goto oom;
+
+				if (!add_variant(
+					    reply,
+					    DBUS_TYPE_STRING,
+					    d->application_name ? (const char * const *) &d->application_name : &empty))
+					goto oom;
+
+			} else if (strcmp(property, "ApplicationDeviceName") == 0) {
+				if (!(reply = dbus_message_new_method_return(m)))
+					goto oom;
+
+				if (!add_variant(
+					    reply,
+					    DBUS_TYPE_STRING,
+					    d->application_device_name ? (const char * const *) &d->application_device_name : &empty))
+					goto oom;
+
+			} else if (strcmp(property, "Priority") == 0) {
+				if (!(reply = dbus_message_new_method_return(m)))
+					goto oom;
+
+				if (!add_variant(
+					    reply,
+					    DBUS_TYPE_INT32,
+					    &d->priority))
+					goto oom;
+			} else {
+				if (!(reply = dbus_message_new_error_printf(
+					      m,
+					      DBUS_ERROR_UNKNOWN_METHOD,
+					      "Unknown property %s",
+					      property)))
+					goto oom;
+			}
+
+			if (!dbus_connection_send(c, reply, NULL))
+				goto oom;
+
+			dbus_message_unref(reply);
+
+			return DBUS_HANDLER_RESULT_HANDLED;
+		}
+
+	} else if (dbus_message_is_method_call(
+			   m,
+			   "org.freedesktop.DBus.Introspectable",
+			   "Introspect")) {
+			    const char *i = introspection;
+
+		if (!(reply = dbus_message_new_method_return(m)))
+			goto oom;
+
+		if (!dbus_message_append_args(
+			    reply,
+			    DBUS_TYPE_STRING,
+			    &i,
+			    DBUS_TYPE_INVALID))
+			goto oom;
+
+		if (!dbus_connection_send(c, reply, NULL))
+			goto oom;
+
+		dbus_message_unref(reply);
+
+		return DBUS_HANDLER_RESULT_HANDLED;
+	}
+
+	return DBUS_HANDLER_RESULT_NOT_YET_HANDLED;
+
+invalid:
+	if (reply)
+		dbus_message_unref(reply);
+
+	if (!(reply = dbus_message_new_error(
+		      m,
+		      DBUS_ERROR_INVALID_ARGS,
+		      "Invalid arguments")))
+		goto oom;
+
+	if (!dbus_connection_send(c, reply, NULL))
+		goto oom;
+
+	dbus_message_unref(reply);
+
+	dbus_error_free(&error);
+
+	return DBUS_HANDLER_RESULT_HANDLED;
+
+oom:
+	if (reply)
+		dbus_message_unref(reply);
+
+	dbus_error_free(&error);
+
+	return DBUS_HANDLER_RESULT_NEED_MEMORY;
+}
+
+static DBusHandlerResult filter_handler(
+	DBusConnection *c,
+	DBusMessage *m,
+	void *userdata) {
+
+	rd_device *d;
+	DBusError error;
+	char *name_owner = NULL;
+
+	dbus_error_init(&error);
+
+	d = userdata;
+	assert(d->ref >= 1);
+
+	if (dbus_message_is_signal(m, "org.freedesktop.DBus", "NameLost")) {
+		const char *name;
+
+		if (!dbus_message_get_args(
+			    m,
+			    &error,
+			    DBUS_TYPE_STRING, &name,
+			    DBUS_TYPE_INVALID))
+			goto invalid;
+
+		if (strcmp(name, d->service_name) == 0 && d->owning) {
+			/* Verify the actual owner of the name to avoid leaked NameLost
+			 * signals from previous reservations. The D-Bus daemon will send
+			 * all messages asynchronously in the correct order, but we could
+			 * potentially process them too late due to the pseudo-blocking
+			 * call mechanism used during both acquisition and release. This
+			 * can happen if we release the device and immediately after
+			 * reacquire it before NameLost is processed. */
+			if (!d->gave_up) {
+				const char *un;
+
+				if ((un = dbus_bus_get_unique_name(c)) && rd_dbus_get_name_owner(c, d->service_name, &name_owner, &error) == 0)
+					if (strcmp(name_owner, un) == 0)
+						goto invalid; /* Name still owned by us */
+			}
+
+			d->owning = 0;
+
+			if (!d->gave_up)  {
+				d->ref++;
+
+				if (d->request_cb)
+					d->request_cb(d, 1);
+				d->gave_up = 1;
+
+				rd_release(d);
+			}
+
+		}
+	}
+
+invalid:
+	free(name_owner);
+	dbus_error_free(&error);
+
+	return DBUS_HANDLER_RESULT_NOT_YET_HANDLED;
+}
+
+
+static const struct DBusObjectPathVTable vtable ={
+	.message_function = object_handler
+};
+
+int rd_acquire(
+	rd_device **_d,
+	DBusConnection *connection,
+	const char *device_name,
+	const char *application_name,
+	int32_t priority,
+	rd_request_cb_t request_cb,
+	DBusError *error) {
+
+	rd_device *d = NULL;
+	int r, k;
+	DBusError _error;
+	DBusMessage *m = NULL, *reply = NULL;
+	dbus_bool_t good;
+
+	if (!error)
+		error = &_error;
+
+	dbus_error_init(error);
+
+	if (!_d)
+		return -EINVAL;
+
+	if (!connection)
+		return -EINVAL;
+
+	if (!device_name)
+		return -EINVAL;
+
+	if (!request_cb && priority != INT32_MAX)
+		return -EINVAL;
+
+	if (!(d = calloc(sizeof(rd_device), 1)))
+		return -ENOMEM;
+
+	d->ref = 1;
+
+	if (!(d->device_name = strdup(device_name))) {
+		r = -ENOMEM;
+		goto fail;
+	}
+
+	if (!(d->application_name = strdup(application_name))) {
+		r = -ENOMEM;
+		goto fail;
+	}
+
+	d->priority = priority;
+	d->connection = dbus_connection_ref(connection);
+	d->request_cb = request_cb;
+
+	if (!(d->service_name = malloc(sizeof(SERVICE_PREFIX) + strlen(device_name)))) {
+		r = -ENOMEM;
+		goto fail;
+	}
+	sprintf(d->service_name, SERVICE_PREFIX "%s", d->device_name);
+
+	if (!(d->object_path = malloc(sizeof(OBJECT_PREFIX) + strlen(device_name)))) {
+		r = -ENOMEM;
+		goto fail;
+	}
+	sprintf(d->object_path, OBJECT_PREFIX "%s", d->device_name);
+
+	if ((k = dbus_bus_request_name(
+		     d->connection,
+		     d->service_name,
+		     DBUS_NAME_FLAG_DO_NOT_QUEUE|
+		     (priority < INT32_MAX ? DBUS_NAME_FLAG_ALLOW_REPLACEMENT : 0),
+		     error)) < 0) {
+		r = -EIO;
+		goto fail;
+	}
+
+	if (k == DBUS_REQUEST_NAME_REPLY_PRIMARY_OWNER)
+		goto success;
+
+	if (k != DBUS_REQUEST_NAME_REPLY_EXISTS) {
+		r = -EIO;
+		goto fail;
+	}
+
+	if (priority <= INT32_MIN) {
+		r = -EBUSY;
+		goto fail;
+	}
+
+	if (!(m = dbus_message_new_method_call(
+		      d->service_name,
+		      d->object_path,
+		      "org.freedesktop.ReserveDevice1",
+		      "RequestRelease"))) {
+		r = -ENOMEM;
+		goto fail;
+	}
+
+	if (!dbus_message_append_args(
+		    m,
+		    DBUS_TYPE_INT32, &d->priority,
+		    DBUS_TYPE_INVALID)) {
+		r = -ENOMEM;
+		goto fail;
+	}
+
+	if (!(reply = dbus_connection_send_with_reply_and_block(
+		      d->connection,
+		      m,
+		      5000, /* 5s */
+		      error))) {
+
+		if (dbus_error_has_name(error, DBUS_ERROR_TIMED_OUT) ||
+		    dbus_error_has_name(error, DBUS_ERROR_UNKNOWN_METHOD) ||
+		    dbus_error_has_name(error, DBUS_ERROR_NO_REPLY)) {
+			/* This must be treated as denied. */
+			r = -EBUSY;
+			goto fail;
+		}
+
+		r = -EIO;
+		goto fail;
+	}
+
+	if (!dbus_message_get_args(
+		    reply,
+		    error,
+		    DBUS_TYPE_BOOLEAN, &good,
+		    DBUS_TYPE_INVALID)) {
+		r = -EIO;
+		goto fail;
+	}
+
+	if (!good) {
+		r = -EBUSY;
+		goto fail;
+	}
+
+	if ((k = dbus_bus_request_name(
+		     d->connection,
+		     d->service_name,
+		     DBUS_NAME_FLAG_DO_NOT_QUEUE|
+		     (priority < INT32_MAX ? DBUS_NAME_FLAG_ALLOW_REPLACEMENT : 0)|
+		     DBUS_NAME_FLAG_REPLACE_EXISTING,
+		     error)) < 0) {
+		r = -EIO;
+		goto fail;
+	}
+
+	if (k != DBUS_REQUEST_NAME_REPLY_PRIMARY_OWNER) {
+		r = -EIO;
+		goto fail;
+	}
+
+success:
+	d->owning = 1;
+
+	if (!(dbus_connection_register_object_path(
+		      d->connection,
+		      d->object_path,
+		      &vtable,
+		      d))) {
+		r = -ENOMEM;
+		goto fail;
+	}
+
+	d->registered = 1;
+
+	if (!dbus_connection_add_filter(
+		    d->connection,
+		    filter_handler,
+		    d,
+		    NULL)) {
+		r = -ENOMEM;
+		goto fail;
+	}
+
+	d->filtering = 1;
+
+	*_d = d;
+	return 0;
+
+fail:
+	if (m)
+		dbus_message_unref(m);
+
+	if (reply)
+		dbus_message_unref(reply);
+
+	if (&_error == error)
+		dbus_error_free(&_error);
+
+	if (d)
+		rd_release(d);
+
+	return r;
+}
+
+void rd_release(
+	rd_device *d) {
+
+	if (!d)
+		return;
+
+	assert(d->ref > 0);
+
+	if (--d->ref > 0)
+		return;
+
+
+	if (d->filtering)
+		dbus_connection_remove_filter(
+			d->connection,
+			filter_handler,
+			d);
+
+	if (d->registered)
+		dbus_connection_unregister_object_path(
+			d->connection,
+			d->object_path);
+
+	if (d->owning)
+		dbus_bus_release_name(
+			d->connection,
+			d->service_name,
+			NULL);
+
+	free(d->device_name);
+	free(d->application_name);
+	free(d->application_device_name);
+	free(d->service_name);
+	free(d->object_path);
+
+	if (d->connection)
+		dbus_connection_unref(d->connection);
+
+	free(d);
+}
+
+int rd_set_application_device_name(rd_device *d, const char *n) {
+	char *t;
+
+	if (!d)
+		return -EINVAL;
+
+	assert(d->ref > 0);
+
+	if (!(t = strdup(n)))
+		return -ENOMEM;
+
+	free(d->application_device_name);
+	d->application_device_name = t;
+	return 0;
+}
+
+void rd_set_userdata(rd_device *d, void *userdata) {
+
+	if (!d)
+		return;
+
+	assert(d->ref > 0);
+	d->userdata = userdata;
+}
+
+void* rd_get_userdata(rd_device *d) {
+
+	if (!d)
+		return NULL;
+
+	assert(d->ref > 0);
+
+	return d->userdata;
+}
+
+int rd_dbus_get_name_owner(
+	DBusConnection *connection,
+	const char *name,
+	char **name_owner,
+	DBusError *error) {
+
+	DBusMessage *msg, *reply;
+	int r;
+
+	*name_owner = NULL;
+
+	if (!(msg = dbus_message_new_method_call(DBUS_SERVICE_DBUS, DBUS_PATH_DBUS, DBUS_INTERFACE_DBUS, "GetNameOwner"))) {
+		r = -ENOMEM;
+		goto fail;
+	}
+
+	if (!dbus_message_append_args(msg, DBUS_TYPE_STRING, &name, DBUS_TYPE_INVALID)) {
+		r = -ENOMEM;
+		goto fail;
+	}
+
+	reply = dbus_connection_send_with_reply_and_block(connection, msg, DBUS_TIMEOUT_USE_DEFAULT, error);
+	dbus_message_unref(msg);
+	msg = NULL;
+
+	if (reply) {
+		if (!dbus_message_get_args(reply, error, DBUS_TYPE_STRING, name_owner, DBUS_TYPE_INVALID)) {
+			dbus_message_unref(reply);
+			r = -EIO;
+			goto fail;
+		}
+
+		*name_owner = strdup(*name_owner);
+		dbus_message_unref(reply);
+
+		if (!*name_owner) {
+			r = -ENOMEM;
+			goto fail;
+		}
+
+	} else if (dbus_error_has_name(error, "org.freedesktop.DBus.Error.NameHasNoOwner"))
+		dbus_error_free(error);
+	else {
+		r = -EIO;
+		goto fail;
+	}
+
+	return 0;
+
+fail:
+	if (msg)
+		dbus_message_unref(msg);
+
+	return r;
+}
diff --git a/libs/ardouralsautil/wscript b/libs/ardouralsautil/wscript
index 9a5d1e5251..75d4eafba4 100644
--- a/libs/ardouralsautil/wscript
+++ b/libs/ardouralsautil/wscript
@@ -19,6 +19,7 @@ def configure(conf):
     autowaf.configure(conf)
     if re.search ("linux", sys.platform) != None and Options.options.dist_target != 'mingw':
         autowaf.check_pkg(conf, 'alsa', uselib_store='ALSA')
+        autowaf.check_pkg(conf, 'dbus-1', uselib_store='DBUS')
 
 def build(bld):
     if re.search ("linux", sys.platform) != None:
@@ -34,4 +35,19 @@ def build(bld):
             obj.use      = 'libpbd'
             obj.uselib   = [ 'ALSA' ]
             obj.vnum     = '0.0.1'
-            obj.install_path  = os.path.join(bld.env['LIBDIR'], 'ardouralsautil')
+            obj.install_path = os.path.join(bld.env['LIBDIR'], 'ardouralsautil')
+
+        if bld.is_defined('HAVE_ALSA') and bld.is_defined('HAVE_DBUS'):
+            obj = bld(features = 'c cprogram')
+            obj.source = [
+                'reserve.c',
+                'request_device.c'
+            ]
+            obj.includes = ['.']
+            obj.target   = 'ardour-request-device'
+            obj.uselib   = [ 'DBUS' ]
+            obj.install_path = os.path.join(bld.env['LIBDIR'], 'ardouralsautil')
+            obj.defines = [
+                    '_POSIX_SOURCE',
+                    '_XOPEN_SOURCE=500',
+            ]