allow-passthrough: Add module to allow passthrough streams always go through

For various use-cases a passthrough stream should have priority over all
other streams and get exclusive access to the sink regardless of whether
any other streams are playing.

An example use-case is ensuring Kodi can successfully start video
playback (with passthrough) even if an external notification sound
happened to be playing at the same time.

Signed-off-by: Arun Raghavan <git@arunraghavan.net>

src/Makefile.am

@@ -1205,7 +1205,8 @@ modlibexec_LTLIBRARIES += \
 		module-switch-on-port-available.la \
 		module-filter-apply.la \
 		module-filter-heuristics.la \
-		module-role-ducking.la
+		module-role-ducking.la \
+		module-allow-passthrough.la
 
 if HAVE_ESOUND
 modlibexec_LTLIBRARIES += \
@@ -1548,7 +1549,8 @@ SYMDEF_FILES = \
 		module-switch-on-connect-symdef.h \
 		module-switch-on-port-available-symdef.h \
 		module-filter-apply-symdef.h \
-		module-filter-heuristics-symdef.h
+		module-filter-heuristics-symdef.h \
+		module-allow-passthrough-symdef.h
 
 if HAVE_ESOUND
 SYMDEF_FILES += \
@@ -2207,6 +2209,12 @@ module_rygel_media_server_la_LDFLAGS = $(MODULE_LDFLAGS)
 module_rygel_media_server_la_LIBADD = $(MODULE_LIBADD) $(DBUS_LIBS) libprotocol-http.la
 module_rygel_media_server_la_CFLAGS = $(AM_CFLAGS) $(DBUS_CFLAGS)
 
+# Allow passthrough module
+module_allow_passthrough_la_SOURCES = modules/module-allow-passthrough.c
+module_allow_passthrough_la_LDFLAGS = $(MODULE_LDFLAGS)
+module_allow_passthrough_la_LIBADD = $(MODULE_LIBADD)
+module_allow_passthrough_la_CFLAGS = $(AM_CFLAGS)
+
 ###################################
 #        Some minor stuff         #
 ###################################

src/modules/module-allow-passthrough.c

@@ -0,0 +1,327 @@
+/***
+  This file is part of PulseAudio.
+
+  Copyright (C) 2014 Collabora Ltd. <http://www.collabora.co.uk/>
+
+  PulseAudio is free software; you can redistribute it and/or modify
+  it under the terms of the GNU Lesser General Public License as published
+  by the Free Software Foundation; either version 2.1 of the License,
+  or (at your option) any later version.
+
+  PulseAudio 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 Lesser General Public License
+  along with PulseAudio; 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 <pulse/xmalloc.h>
+
+#include <pulsecore/core.h>
+#include <pulsecore/i18n.h>
+#include <pulsecore/sink-input.h>
+#include <pulsecore/source-output.h>
+#include <pulsecore/modargs.h>
+#include <pulsecore/log.h>
+#include <pulsecore/namereg.h>
+#include <pulsecore/core-util.h>
+
+#include "module-allow-passthrough-symdef.h"
+
+PA_MODULE_AUTHOR("Guillaume Desmottes");
+PA_MODULE_DESCRIPTION("When a passthrough stream is requested, route all the other streams to a dummy device");
+PA_MODULE_VERSION(PACKAGE_VERSION);
+PA_MODULE_LOAD_ONCE(true);
+
+static const char* const valid_modargs[] = {
+    NULL,
+};
+
+struct userdata {
+    /* (pa_sink *) -> (pa_sink *)
+     * Map the 'real' muted sink to the null-sink currently being used to play
+     * its streams. */
+    pa_hashmap *null_sinks;
+
+    pa_hook_slot
+        *sink_input_new_slot,
+        *sink_input_unlink_slot,
+        *sink_input_move_start_slot,
+        *sink_input_move_finish_slot;
+
+    bool moving;
+};
+
+static pa_sink *ensure_null_sink_for_sink(struct userdata *u, pa_sink *s, pa_core *c) {
+    char *t;
+    pa_module *m;
+    pa_sink *sink;
+    uint32_t idx;
+    const char *name;
+
+    sink = pa_hashmap_get(u->null_sinks, s);
+    if (sink != NULL) {
+        /* We already have a null-sink for this sink */
+        return sink;
+    }
+
+    name = pa_proplist_gets(s->proplist, PA_PROP_MEDIA_NAME);
+
+    t = pa_sprintf_malloc("sink_name=allow_passthrough_null_%s sink_properties='device.description=\"%s\"'",
+                          name ? name : "", _("Dummy Output"));
+    m = pa_module_load(c, "module-null-sink", t);
+    pa_xfree(t);
+
+    if (m == NULL)
+        return NULL;
+
+   PA_IDXSET_FOREACH(sink, c->sinks, idx) {
+        if (sink->module->index == m->index) {
+          pa_hashmap_put(u->null_sinks, s, sink);
+          return sink;
+        }
+    }
+
+   return NULL;
+}
+
+static void unload_null_sink_module_for_sink(struct userdata *u, pa_sink *s, pa_core *c) {
+    pa_sink *null_sink;
+
+    null_sink = pa_hashmap_get(u->null_sinks, s);
+    if (null_sink == NULL)
+        return;
+
+    pa_module_unload_request_by_index(c, null_sink->module->index, true);
+
+    pa_hashmap_remove(u->null_sinks, s);
+}
+
+static void move_stream(struct userdata *u, pa_sink_input *i, pa_sink *target) {
+    u->moving = true;
+    if (pa_sink_input_move_to(i, target, false) < 0)
+        pa_log_info("Failed to move sink input %u \"%s\" to %s.", i->index,
+                    pa_strnull(pa_proplist_gets(i->proplist, PA_PROP_APPLICATION_NAME)), target->name);
+    else
+        pa_log_info("Successfully moved sink input %u \"%s\" to %s.", i->index,
+                    pa_strnull(pa_proplist_gets(i->proplist, PA_PROP_APPLICATION_NAME)), target->name);
+    u->moving = false;
+}
+
+/* Check if @sink has any passthrough stream, ignoring @ignore */
+static bool sink_has_passthrough_stream(pa_sink *sink, pa_sink_input *ignore)
+{
+    pa_sink_input *stream;
+    uint32_t idx;
+
+    PA_IDXSET_FOREACH(stream, sink->inputs, idx) {
+        if (stream == ignore)
+          continue;
+
+        if (pa_sink_input_is_passthrough(stream))
+          return true;
+    }
+
+    return false;
+}
+
+static pa_hook_result_t new_passthrough_stream(struct userdata *u, pa_core *c, pa_sink *sink, pa_sink_input *i) {
+    uint32_t idx;
+    pa_sink_input *stream;
+    pa_sink *null_sink;
+
+    if (sink_has_passthrough_stream(sink, i)) {
+        pa_log_info("Dropping playing a passthrough stream; ignoring");
+        /* PulseAudio will reject the stream itself */
+        return PA_HOOK_OK;
+    }
+
+    pa_log_info("Just received a passthrough stream; pause all the others streams so it can play");
+
+    null_sink = ensure_null_sink_for_sink(u, sink, c);
+    if (null_sink == NULL)
+        return PA_HOOK_OK;
+
+    PA_IDXSET_FOREACH(stream, sink->inputs, idx) {
+        /* We don't want to move the stream which just moved to the sink and trigger this re-routing */
+        if (stream != i)
+          move_stream(u, stream, null_sink);
+    }
+
+    return PA_HOOK_OK;
+}
+
+/* return a null sink for the new stream if it needs to be re-routed */
+static pa_sink * new_normal_stream(struct userdata *u, pa_core *c, pa_sink *sink) {
+    if (!sink_has_passthrough_stream(sink, NULL))
+        return NULL;
+
+    /* A passthrough stream is already playing on this sink, re-route to a null sink */
+    return ensure_null_sink_for_sink(u, sink, c);
+}
+
+static pa_hook_result_t sink_input_new_cb(pa_core *core, pa_sink_input_new_data *new_data, struct userdata *u) {
+    pa_sink *null_sink;
+
+    pa_core_assert_ref(core);
+    /* This is a bit of a hack, to determine whether the input stream will use
+     * a passthrough stream, the sink should have been selected and a format
+     * renegotiated. This can either happen by an earlier module (e.g. one
+     * doing routing or other policies) and if not pulseaudio core will setup
+     * the defaults after all hooks for this event have been processed.
+     *
+     * Unfortunately if no other module decides on sink/format before this hook
+     * runs, pulse core doing it is too late, so if a sink and/or stream format
+     * haven't been setup & configured just yet do so now using the same code
+     * as pulsecore would use (default sink and higher priority negotiated
+     * format). */
+    if (!new_data->sink) {
+        pa_sink *sink = pa_namereg_get(core, NULL, PA_NAMEREG_SINK);
+        pa_return_val_if_fail(sink, -PA_ERR_NOENTITY);
+        pa_sink_input_new_data_set_sink(new_data, sink, false);
+    }
+
+    if (!new_data->format && new_data->nego_formats && !pa_idxset_isempty(new_data->nego_formats))
+      new_data->format = pa_format_info_copy(pa_idxset_first(new_data->nego_formats, NULL));
+
+    if (pa_sink_input_new_data_is_passthrough(new_data))
+        return new_passthrough_stream(u, core, new_data->sink, NULL);
+
+    null_sink = new_normal_stream(u, core, new_data->sink);
+
+    if (null_sink) {
+        pa_log_info("Already playing a passthrough stream; re-routing new stream to the null sink");
+        pa_sink_input_new_data_set_sink(new_data, null_sink, false);
+    }
+
+    return PA_HOOK_OK;
+}
+
+static pa_hook_result_t passthrough_stream_removed(struct userdata *u, pa_core *c, pa_sink_input *i) {
+    uint32_t idx;
+    pa_sink_input *stream;
+    pa_sink *null_sink;
+
+    pa_assert(i->sink);
+
+    null_sink = pa_hashmap_get(u->null_sinks, i->sink);
+    if (null_sink == NULL)
+        return PA_HOOK_OK;
+
+    pa_log_info("Passthrough stream removed; restore all streams");
+
+    PA_IDXSET_FOREACH(stream, null_sink->inputs, idx) {
+        move_stream(u, stream, i->sink);
+    }
+
+    unload_null_sink_module_for_sink(u, i->sink, c);
+
+    return PA_HOOK_OK;
+}
+
+static pa_hook_result_t sink_input_removed(pa_core *core, pa_sink_input *i, struct userdata *u) {
+    pa_sink_input_assert_ref(i);
+
+    if (pa_sink_input_is_passthrough(i))
+      return passthrough_stream_removed(u, core, i);
+
+    return PA_HOOK_OK;
+}
+
+static pa_hook_result_t sink_input_unlink_cb(pa_core *core, pa_sink_input *i, struct userdata *u) {
+    return sink_input_removed(core, i, u);
+}
+
+static pa_hook_result_t sink_input_move_start_cb(pa_core *core, pa_sink_input *i, struct userdata *u) {
+    if (u->moving)
+      return PA_HOOK_OK;
+
+    return sink_input_removed(core, i, u);
+}
+
+static pa_hook_result_t sink_input_move_finish_cb(pa_core *core, pa_sink_input *i, struct userdata *u) {
+    pa_sink *null_sink;
+
+    if (u->moving)
+        return PA_HOOK_OK;
+
+    if (pa_sink_input_is_passthrough(i))
+        /* Passthrough stream has been moved to a new sink */
+        return new_passthrough_stream(u, core, i->sink, i);
+
+    null_sink = new_normal_stream(u, core, i->sink);
+    if (null_sink) {
+        pa_log_info("Already playing a passthrough stream; re-routing moved stream to the null sink");
+        move_stream(u, i, null_sink);
+    }
+
+    return PA_HOOK_OK;
+}
+
+int pa__init(pa_module*m) {
+    pa_modargs *ma;
+    struct userdata *u;
+
+    pa_assert(m);
+
+    if (!(ma = pa_modargs_new(m->argument, valid_modargs))) {
+        pa_log("Failed to parse module arguments");
+        return -1;
+    }
+
+    m->userdata = u = pa_xnew(struct userdata, 1);
+
+    u->null_sinks = pa_hashmap_new(pa_idxset_trivial_hash_func, pa_idxset_trivial_compare_func);
+
+    u->sink_input_new_slot = pa_hook_connect(&m->core->hooks[PA_CORE_HOOK_SINK_INPUT_NEW], PA_HOOK_LATE, (pa_hook_cb_t) sink_input_new_cb, u);
+    u->sink_input_unlink_slot = pa_hook_connect(&m->core->hooks[PA_CORE_HOOK_SINK_INPUT_UNLINK], PA_HOOK_LATE, (pa_hook_cb_t) sink_input_unlink_cb, u);
+    u->sink_input_move_start_slot = pa_hook_connect(&m->core->hooks[PA_CORE_HOOK_SINK_INPUT_MOVE_START], PA_HOOK_LATE, (pa_hook_cb_t) sink_input_move_start_cb, u);
+    u->sink_input_move_finish_slot = pa_hook_connect(&m->core->hooks[PA_CORE_HOOK_SINK_INPUT_MOVE_FINISH], PA_HOOK_LATE, (pa_hook_cb_t) sink_input_move_finish_cb, u);
+
+    u->moving = false;
+
+    pa_modargs_free(ma);
+    return 0;
+}
+
+static void unload_all_null_sink_modules(struct userdata *u, pa_core *c) {
+    void *state = NULL;
+    pa_sink *null_sink;
+
+    PA_HASHMAP_FOREACH(null_sink, u->null_sinks, state)
+        pa_module_unload_request_by_index(c, null_sink->module->index, true);
+}
+
+void pa__done(pa_module*m) {
+    struct userdata *u;
+
+    pa_assert(m);
+
+    if (!(u = m->userdata))
+        return;
+
+    if (u->sink_input_new_slot)
+        pa_hook_slot_free(u->sink_input_new_slot);
+    if (u->sink_input_unlink_slot)
+        pa_hook_slot_free(u->sink_input_unlink_slot);
+    if (u->sink_input_move_start_slot)
+        pa_hook_slot_free(u->sink_input_move_start_slot);
+    if (u->sink_input_move_finish_slot)
+        pa_hook_slot_free(u->sink_input_move_finish_slot);
+
+    if (m->core->state != PA_CORE_SHUTDOWN)
+        unload_all_null_sink_modules(u, m->core);
+
+    if (u->null_sinks)
+        pa_hashmap_free(u->null_sinks);
+
+    pa_xfree(u);
+}