[Qemu-devel] [RFC PATCH v1 5/9] replay: make locking visible outside replay code

["Alex Bennée" <alex.bennee@linaro.org>]

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>
---
 include/sysemu/replay.h  | 14 ++++++++++++++
 replay/replay-internal.c |  5 ++---
 replay/replay-internal.h |  5 ++---
 stubs/replay.c           | 15 +++++++++++++++
 4 files changed, 33 insertions(+), 6 deletions(-)

diff --git a/include/sysemu/replay.h b/include/sysemu/replay.h
index f1c0712795..08bffa2dc2 100644
--- a/include/sysemu/replay.h
+++ b/include/sysemu/replay.h
@@ -46,6 +46,20 @@ 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);
+bool replay_mutex_locked(void);
+
 /* Replay process control functions */
 
 /*! Enables recording or saving event log with specified parameters */
diff --git a/replay/replay-internal.c b/replay/replay-internal.c
index 157c863e25..e6b2fdb6c1 100644
--- a/replay/replay-internal.c
+++ b/replay/replay-internal.c
@@ -181,7 +181,7 @@ void replay_mutex_destroy(void)
 
 static __thread bool replay_locked;
 
-static bool replay_mutex_locked(void)
+bool replay_mutex_locked(void)
 {
     return replay_locked;
 }
@@ -204,7 +204,7 @@ void replay_mutex_unlock(void)
 void replay_save_instructions(void)
 {
     if (replay_file && replay_mode == REPLAY_MODE_RECORD) {
-        replay_mutex_lock();
+        g_assert(replay_mutex_locked());
         int diff = (int)(replay_get_current_step() - replay_state.current_step);
 
         /* Time can only go forward */
@@ -215,6 +215,5 @@ void replay_save_instructions(void)
             replay_put_dword(diff);
             replay_state.current_step += diff;
         }
-        replay_mutex_unlock();
     }
 }
diff --git a/replay/replay-internal.h b/replay/replay-internal.h
index ed66ed803c..b0cf78f16f 100644
--- a/replay/replay-internal.h
+++ b/replay/replay-internal.h
@@ -97,12 +97,11 @@ 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);
 
 /*! Checks error status of the file. */
 void replay_check_error(void);
diff --git a/stubs/replay.c b/stubs/replay.c
index 9c8aa48c9c..39c5746043 100644
--- a/stubs/replay.c
+++ b/stubs/replay.c
@@ -72,3 +72,18 @@ uint64_t blkreplay_next_id(void)
 {
     return 0;
 }
+
+void replay_mutex_lock(void)
+{
+    abort();
+}
+
+void replay_mutex_unlock(void)
+{
+    abort();
+}
+
+bool replay_mutex_locked(void)
+{
+    return false;
+}
-- 
2.11.0