[pulseaudio-discuss] [PATCH v1 18/18] bluetooth-experimental: Fix race condition using accesstype "?"

[Mikel Astiz]

From: Mikel Astiz <mikel.astiz at bmw-carit.de>

BlueZ now supports a flag in the accesstype in order to avoid the race
condition between the state-test (state should be "Playing") and the
call to Acquire(). This fixes the previously existing race condition
during profile change.
---
 src/modules/bluetooth/module-bluetooth-device.c |   15 +++++++--------
 1 files changed, 7 insertions(+), 8 deletions(-)

diff --git a/src/modules/bluetooth/module-bluetooth-device.c b/src/modules/bluetooth/module-bluetooth-device.c
index 3b94f00..fd858c7 100644
--- a/src/modules/bluetooth/module-bluetooth-device.c
+++ b/src/modules/bluetooth/module-bluetooth-device.c
@@ -306,7 +306,6 @@ static void bt_transport_close_stream(struct userdata *u) {
 }
 
 static void bt_transport_release(struct userdata *u) {
-    const char *accesstype = "rw";
     const pa_bluetooth_transport *t;
 
     /* Ignore if already released */
@@ -317,7 +316,7 @@ static void bt_transport_release(struct userdata *u) {
 
     t = pa_bluetooth_discovery_get_transport(u->discovery, u->transport);
     if (t)
-        pa_bluetooth_transport_release(t, accesstype);
+        pa_bluetooth_transport_release(t, u->accesstype);
 
     pa_xfree(u->accesstype);
     u->accesstype = NULL;
@@ -348,7 +347,7 @@ static pa_bt_audio_state_t get_profile_audio_state(const struct userdata *u, con
 }
 
 static int bt_transport_acquire(struct userdata *u, pa_bool_t start) {
-    const char *accesstype = "rw";
+    const char *accesstype = start ? "rw" : "rw?";
     const pa_bluetooth_device *d;
     const pa_bluetooth_transport *t;
 
@@ -375,13 +374,13 @@ static int bt_transport_acquire(struct userdata *u, pa_bool_t start) {
     }
 
     if (!start) {
-        /* FIXME: we are trying to acquire the transport only if the stream is
+        /* We are trying to acquire the transport only if the stream is
            playing, without actually initiating the stream request from our side
            (which is typically undesireable specially for hfgw use-cases.
-           However this approach is racy, since the stream could have been
-           suspended in the meantime, so we can't really guarantee that the
-           stream will not be requested until BlueZ's API supports this
-           atomically. */
+           However this approach is racy unless at least BlueZ version 4.xxx is
+           being used, where the "?" accesstype is supported. The reason is that
+           the stream could have been suspended just before our call to
+           Acquire() */
         if (get_profile_audio_state(u, d) < PA_BT_AUDIO_STATE_PLAYING) {
             pa_log_info("Failed optional acquire of transport %s", u->transport);
             return -1;
-- 
1.7.7.6