softmmu: add trace point when bdrv_flush_all fails

The VM stop process has to flush outstanding I/O and this is a critical
failure scenario that is hard to diagnose. Add a probe point that
records the flush return code.

Reviewed-by: Connor Kuehl <ckuehl@redhat.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>

2 files changed, 9 insertions, 1 deletions

diff --git a/softmmu/cpus.c b/softmmu/cpus.c
index a7ee431..c3caaeb 100644
--- a/softmmu/cpus.c
+++ b/softmmu/cpus.c
@@ -44,6 +44,7 @@
 #include "sysemu/whpx.h"
 #include "hw/boards.h"
 #include "hw/hw.h"
+#include "trace.h"
 
 #ifdef CONFIG_LINUX
 
@@ -266,6 +267,7 @@ static int do_vm_stop(RunState state, bool send_stop)
 
     bdrv_drain_all();
     ret = bdrv_flush_all();
+    trace_vm_stop_flush_all(ret);
 
     return ret;
 }
@@ -704,12 +706,15 @@ int vm_stop_force_state(RunState state)
     if (runstate_is_running()) {
         return vm_stop(state);
     } else {
+        int ret;
         runstate_set(state);
 
         bdrv_drain_all();
         /* Make sure to return an error if the flush in a previous vm_stop()
          * failed. */
-        return bdrv_flush_all();
+        ret = bdrv_flush_all();
+        trace_vm_stop_flush_all(ret);
+        return ret;
     }
 }
 
diff --git a/softmmu/trace-events b/softmmu/trace-events
index 5262828..d18ac41 100644
--- a/softmmu/trace-events
+++ b/softmmu/trace-events
@@ -19,6 +19,9 @@ flatview_new(void *view, void *root) "%p (root %p)"
 flatview_destroy(void *view, void *root) "%p (root %p)"
 flatview_destroy_rcu(void *view, void *root) "%p (root %p)"
 
+# softmmu.c
+vm_stop_flush_all(int ret) "ret %d"
+
 # vl.c
 vm_state_notify(int running, int reason, const char *reason_str) "running %d reason %d (%s)"
 load_file(const char *name, const char *path) "name %s location %s"