replay: fix save/load vm for non-empty queue

This patch does not allows saving/loading vmstate when
replay events queue is not empty. There is no reliable
way to save events queue, because it describes internal
coroutine state. Therefore saving and loading operations
should be deferred to another record/replay step.

Signed-off-by: Pavel Dovgalyuk <pavel.dovgaluk@ispras.ru>
Message-Id: <20180227095214.1060.32939.stgit@pasha-VirtualBox>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Pavel Dovgalyuk <Pavel.Dovgaluk@ispras.ru>

include/sysemu/replay.h

@@ -166,5 +166,8 @@ void replay_audio_in(int *recorded, void *samples, int *wpos, int size);
 /*! Called at the start of execution.
     Loads or saves initial vmstate depending on execution mode. */
 void replay_vmstate_init(void);
+/*! Called to ensure that replay state is consistent and VM snapshot
+    can be created */
+bool replay_can_snapshot(void);
 
 #endif

migration/savevm.c

@@ -54,6 +54,7 @@
 #include "qemu/cutils.h"
 #include "io/channel-buffer.h"
 #include "io/channel-file.h"
+#include "sysemu/replay.h"
 
 #ifndef ETH_P_RARP
 #define ETH_P_RARP 0x8035
@@ -2197,6 +2198,12 @@ int save_snapshot(const char *name, Error **errp)
     struct tm tm;
     AioContext *aio_context;
 
+    if (!replay_can_snapshot()) {
+        error_report("Record/replay does not allow making snapshot "
+                     "right now. Try once more later.");
+        return ret;
+    }
+
     if (!bdrv_all_can_snapshot(&bs)) {
         error_setg(errp, "Device '%s' is writable but does not support "
                    "snapshots", bdrv_get_device_name(bs));
@@ -2388,6 +2395,12 @@ int load_snapshot(const char *name, Error **errp)
     AioContext *aio_context;
     MigrationIncomingState *mis = migration_incoming_get_current();
 
+    if (!replay_can_snapshot()) {
+        error_report("Record/replay does not allow loading snapshot "
+                     "right now. Try once more later.");
+        return -EINVAL;
+    }
+
     if (!bdrv_all_can_snapshot(&bs)) {
         error_setg(errp,
                    "Device '%s' is writable but does not support snapshots",

replay/replay-snapshot.c

@@ -83,3 +83,9 @@ void replay_vmstate_init(void)
         }
     }
 }
+
+bool replay_can_snapshot(void)
+{
+    return replay_mode == REPLAY_MODE_NONE
+        || !replay_has_events();
+}