Patchwork [v7,12/13] trace-state: [stderr] add support for dynamically enabling/disabling events

diff --git a/configure b/configure
index c49c080..623d40f 100755
--- a/configure
+++ b/configure
@@ -3071,6 +3071,9 @@  fi
 if test "$trace_backend" = "simple"; then
   echo "CONFIG_TRACE_SIMPLE=y" >> $config_host_mak
 fi
+if test "$trace_backend" = "stderr"; then
+  echo "CONFIG_TRACE_STDERR=y" >> $config_host_mak
+fi
 # Set the appropriate trace file.
 if test "$trace_backend" = "simple"; then
   trace_file="\"$trace_file-\" FMT_pid"
diff --git a/docs/tracing.txt b/docs/tracing.txt
index 448fdef..f14dbe3 100644
--- a/docs/tracing.txt
+++ b/docs/tracing.txt
@@ -164,11 +164,6 @@  effectively turns trace events into debug printfs.
 This is the simplest backend and can be used together with existing code that
 uses DPRINTF().
 
-Note that with this backend trace events cannot be programmatically
-enabled/disabled. Thus, in order to trim down the amount of output and the
-performance impact of tracing, you might want to add the "disable" property in
-the "trace-events" file for those events you are not interested in.
-
 === Simpletrace ===
 
 The "simple" backend supports common use cases and comes as part of the QEMU
diff --git a/qemu-options.hx b/qemu-options.hx
index 91144d9..455f1ef 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -2450,7 +2450,8 @@  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.
+This option is only available when using the @var{simple} and @var{stderr}
+tracing backends.
 @item file=@var{file}
 Log output traces to @var{file}.
 
diff --git a/scripts/tracetool b/scripts/tracetool
index c740080..743d246 100755
--- a/scripts/tracetool
+++ b/scripts/tracetool
@@ -241,7 +241,12 @@  linetoh_begin_stderr()
 {
     cat <<EOF
 #include <stdio.h>
+#include "trace/stderr.h"
+
+extern TraceEvent trace_list[];
 EOF
+
+    stderr_event_num=0
 }
 
 linetoh_stderr()
@@ -260,29 +265,47 @@  linetoh_stderr()
     cat <<EOF
 static inline void trace_$name($args)
 {
-    fprintf(stderr, "$name $fmt\n" $argnames);
+    if (trace_list[$stderr_event_num].state != 0) {
+        fprintf(stderr, "$name $fmt\n" $argnames);
+    }
 }
 EOF
+    stderr_event_num=$((stderr_event_num + 1))
+
 }
 
 linetoh_end_stderr()
 {
-return
+    cat <<EOF
+#define NR_TRACE_EVENTS $stderr_event_num
+EOF
 }
 
 linetoc_begin_stderr()
 {
-return
+    cat <<EOF
+#include "trace.h"
+
+TraceEvent trace_list[] = {
+EOF
+    stderr_event_num=0
 }
 
 linetoc_stderr()
 {
-return
+    local name
+    name=$(get_name "$1")
+    cat <<EOF
+{.tp_name = "$name", .state=0},
+EOF
+    stderr_event_num=$(($stderr_event_num + 1))
 }
 
 linetoc_end_stderr()
 {
-return
+    cat <<EOF
+};
+EOF
 }
 #END OF STDERR
 
diff --git a/trace/stderr.c b/trace/stderr.c
index 480a6b7..61debfa 100644
--- a/trace/stderr.c
+++ b/trace/stderr.c
@@ -1,21 +1,33 @@ 
+#include "trace.h"
 #include "trace/control.h"
 
 
 void trace_print_events (FILE *stream, fprintf_function stream_printf)
 {
-    fprintf(stderr, "qemu: warning: cannot print the trace events with the current backend\n");
-    stream_printf(stream, "error: operation not supported with the current backend\n");
+    unsigned int i;
+
+    for (i = 0; i < NR_TRACE_EVENTS; i++) {
+        stream_printf(stream, "%s [Event ID %u] : state %u\n",
+                      trace_list[i].tp_name, i, trace_list[i].state);
+    }
 }
 
 bool trace_event_set_state (const char *name, bool state)
 {
-    fprintf(stderr, "qemu: warning: cannot set the state of a trace event with the current backend\n");
+    unsigned int i;
+
+    for (i = 0; i < NR_TRACE_EVENTS; i++) {
+        if (!strcmp(trace_list[i].tp_name, name)) {
+            trace_list[i].state = state;
+            return true;
+        }
+    }
     return false;
 }
 
 bool trace_config_init (void)
 {
-    return false;
+    return true;
 }
 
 bool trace_config_init_file (const char *file)
diff --git a/trace/stderr.h b/trace/stderr.h
new file mode 100644
index 0000000..d575b61
--- /dev/null
+++ b/trace/stderr.h
@@ -0,0 +1,11 @@ 
+#ifndef TRACE_STDERR_H
+#define TRACE_STDERR_H
+
+typedef uint64_t TraceEventID;
+
+typedef struct {
+    const char *tp_name;
+    bool state;
+} TraceEvent;
+
+#endif /* ! TRACE_STDERR_H */