trace: Specify trace file name

Allow users to specify a file for trace-outputs at configuration.
Also, allow trace files to be annotated by <pid> so each qemu instance has
unique traces.

The trace file name can be passed as a config option:
--trace-file=/path/to/file
(Default: trace )
At runtime, the pid of the qemu process is appended to the filename so
that mutiple qemu instances do not have overlapping logs.

Eg : trace-1234 for qemu launched with pid 1234.

I have yet to test this on windows. getpid() is used at many places
in code(including vnc.c), so I'm hoping this would be okay too.

Edited-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>

1 files changed, 17 insertions, 4 deletions

diff --git a/simpletrace.c b/simpletrace.c
index 688959a9fe..97045a6732 100644
--- a/simpletrace.c
+++ b/simpletrace.c
@@ -54,13 +54,26 @@ static bool write_header(FILE *fp)
     return fwrite(&header, sizeof header, 1, fp) == 1;
 }
 
+static bool open_trace_file(void)
+{
+    char *filename;
+
+    if (asprintf(&filename, CONFIG_TRACE_FILE, getpid()) < 0) {
+        return false;
+    }
+
+    trace_fp = fopen(filename, "w");
+    free(filename);
+    if (!trace_fp) {
+        return false;
+    }
+    return write_header(trace_fp);
+}
+
 static void flush_trace_buffer(void)
 {
     if (!trace_fp) {
-        trace_fp = fopen("trace.log", "w");
-        if (trace_fp) {
-            write_header(trace_fp);
-        }
+        open_trace_file();
     }
     if (trace_fp) {
         size_t unused; /* for when fwrite(3) is declared warn_unused_result */