replay: make locking visible outside replay code

The replay_mutex_lock/unlock/locked functions are now going to be used
for ensuring lock-step behaviour between the two threads. Make them
public API functions and also provide stubs for non-QEMU builds on
common paths.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Pavel Dovgalyuk <pavel.dovgaluk@ispras.ru>
Message-Id: <20180227095242.1060.16601.stgit@pasha-VirtualBox>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

include/sysemu/replay.h

@@ -48,6 +48,19 @@ extern ReplayMode replay_mode;
 /* Name of the initial VM snapshot */
 extern char *replay_snapshot;
 
+/* Replay locking
+ *
+ * The locks are needed to protect the shared structures and log file
+ * when doing record/replay. They also are the main sync-point between
+ * the main-loop thread and the vCPU thread. This was a role
+ * previously filled by the BQL which has been busy trying to reduce
+ * its impact across the code. This ensures blocks of events stay
+ * sequential and reproducible.
+ */
+
+void replay_mutex_lock(void);
+void replay_mutex_unlock(void);
+
 /* Replay process control functions */
 
 /*! Enables recording or saving event log with specified parameters */

replay/replay-internal.c

@@ -181,7 +181,7 @@ void replay_mutex_destroy(void)
     qemu_mutex_destroy(&lock);
 }
 
-static bool replay_mutex_locked(void)
+bool replay_mutex_locked(void)
 {
     return replay_locked;
 }

replay/replay-internal.h

@@ -100,12 +100,12 @@ int64_t replay_get_qword(void);
 void replay_get_array(uint8_t *buf, size_t *size);
 void replay_get_array_alloc(uint8_t **buf, size_t *size);
 
-/* Mutex functions for protecting replay log file */
+/* Mutex functions for protecting replay log file and ensuring
+ * synchronisation between vCPU and main-loop threads. */
 
 void replay_mutex_init(void);
 void replay_mutex_destroy(void);
-void replay_mutex_lock(void);
-void replay_mutex_unlock(void);
+bool replay_mutex_locked(void);
 
 /*! Checks error status of the file. */
 void replay_check_error(void);

stubs/replay.c

@@ -72,3 +72,11 @@ uint64_t blkreplay_next_id(void)
 {
     return 0;
 }
+
+void replay_mutex_lock(void)
+{
+}
+
+void replay_mutex_unlock(void)
+{
+}