Re: [Qemu-devel] [PATCH 02/12] trace+libvirt: start trace processing thread in final child process

[Michael Mueller <mimu@linux.vnet.ibm.com>]

On Tue, 16 Jul 2013 11:05:11 +0800
Stefan Hajnoczi <stefanha@gmail.com> wrote:

> On Mon, Jul 15, 2013 at 09:41:19PM +0200, Christian Borntraeger wrote:
> > 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) This results in stale qemu
> > processes. Fix this by deferring trace initialization.
> 
> I don't think this works since trace events will fill up trace_buf[]
> and eventually invoke flush_trace_file().
> 
> At that point we use trace_available_cond and trace_empty_cond, which
> may be NULL in Glib <2.31.0.
> 
> Perhaps this can be made safe by checking trace_writeout_enabled.  It
> will be false before the backend has been initialized.
> 
> Stefan
> 

You mean something like this. I'll give it a try:

---
 trace/simple.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/trace/simple.c
+++ b/trace/simple.c
@@ -53,7 +53,7 @@ static GCond *trace_empty_cond;
 #endif
 
 static bool trace_available;
-static bool trace_writeout_enabled;
+static bool trace_writeout_enabled = false;
 
 enum {
     TRACE_BUF_LEN = 4096 * 64,
@@ -427,5 +427,6 @@ bool trace_backend_init(const char *even
     atexit(st_flush_trace_buffer);
     trace_backend_init_events(events);
     st_set_trace_file(file);
+    trace_writeout_enabled = false;
     return true;
 }

Michael