trace: Add wildcard trace event support

A basic wildcard matching is supported in both the monitor command
"trace-event" and the events list file. That means you can enable/disable
the events having a common prefix in a batch. For example, virtio-blk trace
events could be enabled using:
    trace-event virtio_blk_* on

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

docs/tracing.txt

@@ -132,12 +132,19 @@ This functionality is also provided through monitor commands:
   means disabled.
 
 * trace-event NAME on|off
-  Enable/disable a given trace event.
+  Enable/disable a given trace event or a group of events having common prefix
+  through wildcard.
 
 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.
 
+A basic wildcard matching is supported in both the monitor command "trace
+-event" and the events list file. That means you can enable/disable the events
+having a common prefix in a batch. For example, virtio-blk trace events could
+be enabled using:
+  trace-event virtio_blk_* on
+
 == Trace backends ==
 
 The "tracetool" script automates tedious trace event code generation and also

trace/simple.c

@@ -324,14 +324,29 @@ void trace_print_events(FILE *stream, fprintf_function stream_printf)
 bool trace_event_set_state(const char *name, bool state)
 {
     unsigned int i;
+    unsigned int len;
+    bool wildcard = false;
+    bool matched = false;
 
+    len = strlen(name);
+    if (len > 0 && name[len - 1] == '*') {
+        wildcard = true;
+        len -= 1;
+    }
     for (i = 0; i < NR_TRACE_EVENTS; i++) {
+        if (wildcard) {
+            if (!strncmp(trace_list[i].tp_name, name, len)) {
+                trace_list[i].state = state;
+                matched = true;
+            }
+            continue;
+        }
         if (!strcmp(trace_list[i].tp_name, name)) {
             trace_list[i].state = state;
             return true;
         }
     }
-    return false;
+    return matched;
 }
 
 /* Helper function to create a thread with signals blocked.  Use glib's

trace/stderr.c

@@ -15,14 +15,29 @@ void trace_print_events(FILE *stream, fprintf_function stream_printf)
 bool trace_event_set_state(const char *name, bool state)
 {
     unsigned int i;
+    unsigned int len;
+    bool wildcard = false;
+    bool matched = false;
 
+    len = strlen(name);
+    if (len > 0 && name[len - 1] == '*') {
+        wildcard = true;
+        len -= 1;
+    }
     for (i = 0; i < NR_TRACE_EVENTS; i++) {
+        if (wildcard) {
+            if (!strncmp(trace_list[i].tp_name, name, len)) {
+                trace_list[i].state = state;
+                matched = true;
+            }
+            continue;
+        }
         if (!strcmp(trace_list[i].tp_name, name)) {
             trace_list[i].state = state;
             return true;
         }
     }
-    return false;
+    return matched;
 }
 
 bool trace_backend_init(const char *events, const char *file)