trace: Add trace-file command to open/close/flush trace file

This patch adds the trace-file command:

  trace-file [on|off|flush]

  Open, close, or flush the trace file.  If no argument is given,
  the status of the trace file is displayed.

The trace file is turned on by default but is only written out when the
trace buffer becomes full.  The flush operation can be used to force
write out at any time.

Turning off the trace file does not change the state of trace events;
tracing will continue to the trace buffer.  When the trace file is off,
use "info trace" to display the contents of the trace buffer in memory.

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

This commit also contains the trace-file sub-command from the following
commit:

commit 5ce8d1a957afae2c52ad748944ce72848ccf57bd
Author: Prerna Saxena <prerna@linux.vnet.ibm.com>
Date:   Wed Aug 4 16:23:54 2010 +0530

    trace: Add options to specify trace file name at startup and runtime

    This patch adds an optional command line switch '-trace' to specify the
    filename to write traces to, when qemu starts.
    Eg, If compiled with the 'simple' trace backend,
    [temp@system]$ qemu -trace FILENAME IMAGE
    Allows the binary traces to be written to FILENAME instead of the option
    set at config-time.

    Also, this adds monitor sub-command 'set' to trace-file commands to
    dynamically change trace log file at runtime.
    Eg,
    (qemu)trace-file set FILENAME
    This allows one to set trace outputs to FILENAME from the default
    specified at startup.

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

1 files changed, 47 insertions, 13 deletions

diff --git a/simpletrace.c b/simpletrace.c
index 97045a6732..f849e42914 100644
--- a/simpletrace.c
+++ b/simpletrace.c
@@ -42,6 +42,14 @@ enum {
 static TraceRecord trace_buf[TRACE_BUF_LEN];
 static unsigned int trace_idx;
 static FILE *trace_fp;
+static char *trace_file_name = NULL;
+static bool trace_file_enabled = false;
+
+void st_print_trace_file_status(FILE *stream, int (*stream_printf)(FILE *stream, const char *fmt, ...))
+{
+    stream_printf(stream, "Trace file \"%s\" %s.\n",
+                  trace_file_name, trace_file_enabled ? "on" : "off");
+}
 
 static bool write_header(FILE *fp)
 {
@@ -54,31 +62,57 @@ static bool write_header(FILE *fp)
     return fwrite(&header, sizeof header, 1, fp) == 1;
 }
 
-static bool open_trace_file(void)
+/**
+ * set_trace_file : To set the name of a trace file.
+ * @file : pointer to the name to be set.
+ *         If NULL, set to the default name-<pid> set at config time.
+ */
+bool st_set_trace_file(const char *file)
 {
-    char *filename;
+    st_set_trace_file_enabled(false);
 
-    if (asprintf(&filename, CONFIG_TRACE_FILE, getpid()) < 0) {
-        return false;
-    }
+    free(trace_file_name);
 
-    trace_fp = fopen(filename, "w");
-    free(filename);
-    if (!trace_fp) {
-        return false;
+    if (!file) {
+        if (asprintf(&trace_file_name, CONFIG_TRACE_FILE, getpid()) < 0) {
+            trace_file_name = NULL;
+            return false;
+        }
+    } else {
+        if (asprintf(&trace_file_name, "%s", file) < 0) {
+            trace_file_name = NULL;
+            return false;
+        }
     }
-    return write_header(trace_fp);
+
+    st_set_trace_file_enabled(true);
+    return true;
 }
 
-static void flush_trace_buffer(void)
+static void flush_trace_file(void)
 {
+    /* If the trace file is not open yet, open it now */
     if (!trace_fp) {
-        open_trace_file();
+        trace_fp = fopen(trace_file_name, "w");
+        if (!trace_fp) {
+            /* Avoid repeatedly trying to open file on failure */
+            trace_file_enabled = false;
+            return;
+        }
+        write_header(trace_fp);
     }
+
     if (trace_fp) {
         size_t unused; /* for when fwrite(3) is declared warn_unused_result */
         unused = fwrite(trace_buf, trace_idx * sizeof(trace_buf[0]), 1, trace_fp);
     }
+}
+
+void st_flush_trace_buffer(void)
+{
+    if (trace_file_enabled) {
+        flush_trace_file();
+    }
 
     /* Discard written trace records */
     trace_idx = 0;
@@ -128,7 +162,7 @@ static void trace(TraceEventID event, uint64_t x1, uint64_t x2, uint64_t x3,
     rec->x6 = x6;
 
     if (++trace_idx == TRACE_BUF_LEN) {
-        flush_trace_buffer();
+        st_flush_trace_buffer();
     }
 }