tracing: start trace processing thread in final child process

When running with trace backend e.g. "simple" the writer thread needs to be
implemented in the same process context as the trace points that will be
processed. Under libvirtd control, qemu gets first started in daemonized
mode to privide its capabilities. Creating the writer thread in the initial
process context then leads to a dead lock because the thread gets termined
together with the initial parent. (-daemonize)

Signed-off-by: Michael Mueller <mimu@linux.vnet.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
[minor whitespace fixes]
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

diff --git a/vl.c b/vl.c
index 7f4fe0d5df59b50f0635ffcb7fb222441035890d..63f4d5585c4b9580e65fbc2b7d2065937c1e29ea 100644 (file)
--- a/vl.c
+++ b/vl.c
@@ -3879,8 +3879,10 @@ int main(int argc, char **argv, char **envp)
         qemu_set_log(mask);
     }
 
-    if (!trace_backend_init(trace_events, trace_file)) {
-        exit(1);
+    if (!is_daemonized()) {
+        if (!trace_backend_init(trace_events, trace_file)) {
+            exit(1);
+        }
     }
 
     /* If no data_dir is specified then try to find it relative to the
@@ -4379,6 +4381,12 @@ int main(int argc, char **argv, char **envp)
 
     os_setup_post();
 
+    if (is_daemonized()) {
+        if (!trace_backend_init(trace_events, trace_file)) {
+            exit(1);
+        }
+    }
+
     main_loop();
     bdrv_close_all();
     pause_all_vcpus();