trace: add "-trace events" argument to control initial state

The "-trace events" argument can be used to provide a file with a list of trace
event names that will be enabled prior to starting execution, thus providing
early tracing.

This saves the user from manually toggling event states through the monitor
interface or whichever backend-specific interface.

Signed-off-by: Lluís Vilanova <vilanova@ac.upc.edu>

9 files changed, 92 insertions, 13 deletions

diff --git a/Makefile.objs b/Makefile.objs
index 57a80e613..036a4eb6a 100644
--- a/Makefile.objs
+++ b/Makefile.objs
@@ -384,6 +384,8 @@ trace-nested-$(CONFIG_TRACE_DEFAULT) += default.o
 trace-nested-$(CONFIG_TRACE_SIMPLE) += simple.o
 trace-obj-$(CONFIG_TRACE_SIMPLE) += qemu-timer-common.o
 
+trace-nested-y += control.o
+
 trace-obj-y += $(addprefix trace/, $(trace-nested-y))
 
 ######################################################################
diff --git a/docs/tracing.txt b/docs/tracing.txt
index 41eb8e6fe..455da3796 100644
--- a/docs/tracing.txt
+++ b/docs/tracing.txt
@@ -138,6 +138,10 @@ This functionality is also provided through monitor commands:
 * trace-event NAME on|off
   Enable/disable a given trace event.
 
+The "-trace events=<file>" command line argument can be used to enable the
+events listed in <file> from the very beginning of the program. This file must
+contain one event name per line.
+
 == Trace backends ==
 
 The "tracetool" script automates tedious trace event code generation and also
diff --git a/qemu-config.c b/qemu-config.c
index 4f3465d38..7a7854fd0 100644
--- a/qemu-config.c
+++ b/qemu-config.c
@@ -309,6 +309,9 @@ static QemuOptsList qemu_trace_opts = {
     .head = QTAILQ_HEAD_INITIALIZER(qemu_trace_opts.head),
     .desc = {
         {
+            .name = "events",
+            .type = QEMU_OPT_STRING,
+        },{
             .name = "file",
             .type = QEMU_OPT_STRING,
         },
diff --git a/qemu-options.hx b/qemu-options.hx
index 2d29933ab..edd181bb8 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -2437,17 +2437,29 @@ Normally QEMU loads a configuration file from @var{sysconfdir}/qemu.conf and
 option will prevent QEMU from loading these configuration files at startup.
 ETEXI
 DEF("trace", HAS_ARG, QEMU_OPTION_trace,
-    "-trace\n"
-    "                Specify a trace file to log traces to\n",
+    "-trace [events=<file>][,file=<file>]\n"
+    "                specify tracing options\n",
     QEMU_ARCH_ALL)
 STEXI
-HXCOMM This line is not accurate, as the option is backend-specific but HX does
-HXCOMM not support conditional compilation of text.
-@item -trace
+HXCOMM This line is not accurate, as some sub-options are backend-specific but
+HXCOMM HX does not support conditional compilation of text.
+@item -trace [events=@var{file}][,file=@var{file}]
 @findex -trace
-Specify a trace file to log output traces to.
 
-This option is available only when using the @var{simple} tracing backend.
+Specify tracing options.
+
+@table @option
+@item events=@var{file}
+Immediately enable events listed in @var{file}.
+The file must contain one event name (as listed in the @var{trace-events} file)
+per line.
+
+This option is only available when using the @var{simple} tracing backend.
+@item file=@var{file}
+Log output traces to @var{file}.
+
+This option is only available when using the @var{simple} tracing backend.
+@end table
 ETEXI
 
 HXCOMM This is the last statement. Insert new options before this line!
diff --git a/trace/control.c b/trace/control.c
new file mode 100644
index 000000000..4c5527d20
--- /dev/null
+++ b/trace/control.c
@@ -0,0 +1,42 @@
+/*
+ * Interface for configuring and controlling the state of tracing events.
+ *
+ * Copyright (C) 2011 Lluís Vilanova <vilanova@ac.upc.edu>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2.  See
+ * the COPYING file in the top-level directory.
+ */
+
+#include "trace/control.h"
+
+
+void trace_backend_init_events(const char *fname)
+{
+    if (fname == NULL) {
+        return;
+    }
+
+    FILE *fp = fopen(fname, "r");
+    if (!fp) {
+        fprintf(stderr, "error: could not open trace events file '%s': %s\n",
+                fname, strerror(errno));
+        exit(1);
+    }
+    char line_buf[1024];
+    while (fgets(line_buf, sizeof(line_buf), fp)) {
+        size_t len = strlen(line_buf);
+        if (len > 1) {              /* skip empty lines */
+            line_buf[len - 1] = '\0';
+            if (!trace_event_set_state(line_buf, true)) {
+                fprintf(stderr,
+                        "error: trace event '%s' does not exist\n", line_buf);
+                exit(1);
+            }
+        }
+    }
+    if (fclose(fp) != 0) {
+        fprintf(stderr, "error: closing file '%s': %s\n",
+                fname, strerror(errno));
+        exit(1);
+    }
+}
diff --git a/trace/control.h b/trace/control.h
index c99b4d50a..2acaa4290 100644
--- a/trace/control.h
+++ b/trace/control.h
@@ -24,10 +24,18 @@ bool trace_event_set_state(const char *name, bool state);
 
 /** Initialize the tracing backend.
  *
- * @file Name of trace output file; may be NULL.
- *       Corresponds to commandline option "-trace file=...".
+ * @events Name of file with events to be enabled at startup; may be NULL.
+ *         Corresponds to commandline option "-trace events=...".
+ * @file   Name of trace output file; may be NULL.
+ *         Corresponds to commandline option "-trace file=...".
  * @return Whether the backend could be successfully initialized.
  */
-bool trace_backend_init(const char *file);
+bool trace_backend_init(const char *events, const char *file);
+
+/** Generic function to initialize the state of events.
+ *
+ * @fname Name of file with events to enable; may be NULL.
+ */
+void trace_backend_init_events(const char *fname);
 
 #endif  /* TRACE_CONTROL_H */
diff --git a/trace/default.c b/trace/default.c
index 3573d5b29..c9b27a289 100644
--- a/trace/default.c
+++ b/trace/default.c
@@ -25,8 +25,13 @@ bool trace_event_set_state(const char *name, bool state)
     return false;
 }
 
-bool trace_backend_init(const char *file)
+bool trace_backend_init(const char *events, const char *file)
 {
+    if (events) {
+        fprintf(stderr, "error: -trace events=...: "
+                "option not supported by the selected tracing backend\n");
+        return false;
+    }
     if (file) {
         fprintf(stderr, "error: -trace file=...: "
                 "option not supported by the selected tracing backend\n");
diff --git a/trace/simple.c b/trace/simple.c
index 70689e948..a6093682d 100644
--- a/trace/simple.c
+++ b/trace/simple.c
@@ -331,7 +331,7 @@ bool trace_event_set_state(const char *name, bool state)
     return false;
 }
 
-bool trace_backend_init(const char *file)
+bool trace_backend_init(const char *events, const char *file)
 {
     pthread_t thread;
     pthread_attr_t attr;
@@ -350,6 +350,7 @@ bool trace_backend_init(const char *file)
         fprintf(stderr, "warning: unable to initialize simple trace backend\n");
     } else {
         atexit(st_flush_trace_buffer);
+        trace_backend_init_events(events);
         st_set_trace_file(file);
     }
 
diff --git a/vl.c b/vl.c
index 60322b62a..c6dc6895b 100644
--- a/vl.c
+++ b/vl.c
@@ -2137,6 +2137,7 @@ int main(int argc, char **argv, char **envp)
         .realloc = realloc_and_trace,
         .free = free_and_trace,
     };
+    const char *trace_events = NULL;
     const char *trace_file = NULL;
 
     atexit(qemu_run_exit_notifiers);
@@ -2934,6 +2935,7 @@ int main(int argc, char **argv, char **envp)
                 if (!opts) {
                     exit(1);
                 }
+                trace_events = qemu_opt_get(opts, "events");
                 trace_file = qemu_opt_get(opts, "file");
                 break;
             }
@@ -2994,7 +2996,7 @@ int main(int argc, char **argv, char **envp)
         set_cpu_log(log_mask);
     }
 
-    if (!trace_backend_init(trace_file)) {
+    if (!trace_backend_init(trace_events, trace_file)) {
         exit(1);
     }