trace: Provide a detailed event control interface

This interface decouples event obtaining from interaction.

Events can be obtained through three different methods:

* identifier
* name
* simple wildcard pattern

Signed-off-by: Lluís Vilanova <vilanova@ac.upc.edu>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

docs/tracing.txt

@@ -100,49 +100,37 @@ respectively.  This ensures portability between 32- and 64-bit platforms.
 
 == Generic interface and monitor commands ==
 
-You can programmatically query and control the dynamic state of trace events
-through a backend-agnostic interface:
+You can programmatically query and control the state of trace events through a
+backend-agnostic interface provided by the header "trace/control.h".
 
-* trace_print_events
+Note that some of the backends do not provide an implementation for some parts
+of this interface, in which case QEMU will just print a warning (please refer to
+header "trace/control.h" to see which routines are backend-dependent).
 
-* trace_event_set_state
-  Enables or disables trace events at runtime inside QEMU.
-  The function returns "true" if the state of the event has been successfully
-  changed, or "false" otherwise:
-
-    #include "trace/control.h"
-
-    trace_event_set_state("virtio_irq", true); /* enable */
-    [...]
-    trace_event_set_state("virtio_irq", false); /* disable */
-
-Note that some of the backends do not provide an implementation for this
-interface, in which case QEMU will just print a warning.
-
-This functionality is also provided through monitor commands:
+The state of events can also be queried and modified through monitor commands:
 
 * info trace-events
   View available trace events and their state.  State 1 means enabled, state 0
   means disabled.
 
 * trace-event NAME on|off
-  Enable/disable a given trace event or a group of events having common prefix
-  through wildcard.
+  Enable/disable a given trace event or a group of events (using wildcards).
 
 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
-
 If a line in the "-trace events=<file>" file begins with a '-', the trace event
 will be disabled instead of enabled.  This is useful when a wildcard was used
 to enable an entire family of events but one noisy event needs to be disabled.
 
+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
+the following monitor command:
+
+    trace-event virtio_blk_* on
+
 == Trace backends ==
 
 The "tracetool" script automates tedious trace event code generation and also
@@ -263,3 +251,7 @@ guard such computations and avoid its compilation when the event is disabled:
         }
         return ptr;
     }
+
+You can check both if the event has been disabled and is dynamically enabled at
+the same time using the 'trace_event_get_state' routine (see header
+"trace/control.h" for more information).

trace/control-internal.h

@@ -0,0 +1,67 @@
+/*
+ * Interface for configuring and controlling the state of tracing events.
+ *
+ * Copyright (C) 2011-2012 Lluís Vilanova <vilanova@ac.upc.edu>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or later.
+ * See the COPYING file in the top-level directory.
+ */
+
+#ifndef TRACE__CONTROL_INTERNAL_H
+#define TRACE__CONTROL_INTERNAL_H
+
+#include <string.h>
+
+
+extern TraceEvent trace_events[];
+
+
+static inline TraceEvent *trace_event_id(TraceEventID id)
+{
+    assert(id < trace_event_count());
+    return &trace_events[id];
+}
+
+static inline TraceEventID trace_event_count(void)
+{
+    return TRACE_EVENT_COUNT;
+}
+
+static inline bool trace_event_is_pattern(const char *str)
+{
+    assert(str != NULL);
+    return strchr(str, '*') != NULL;
+}
+
+static inline TraceEventID trace_event_get_id(TraceEvent *ev)
+{
+    assert(ev != NULL);
+    return ev->id;
+}
+
+static inline const char * trace_event_get_name(TraceEvent *ev)
+{
+    assert(ev != NULL);
+    return ev->name;
+}
+
+static inline bool trace_event_get_state_static(TraceEvent *ev)
+{
+    assert(ev != NULL);
+    return ev->sstate;
+}
+
+static inline bool trace_event_get_state_dynamic(TraceEvent *ev)
+{
+    assert(ev != NULL);
+    return ev->dstate;
+}
+
+static inline void trace_event_set_state_dynamic(TraceEvent *ev, bool state)
+{
+    assert(ev != NULL);
+    assert(trace_event_get_state_static(ev));
+    return trace_event_set_state_dynamic_backend(ev, state);
+}
+
+#endif  /* TRACE__CONTROL_INTERNAL_H */

trace/control.c

@@ -1,19 +1,86 @@
 /*
  * Interface for configuring and controlling the state of tracing events.
  *
- * Copyright (C) 2011 Lluís Vilanova <vilanova@ac.upc.edu>
+ * Copyright (C) 2011-2012 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.
+ * This work is licensed under the terms of the GNU GPL, version 2 or later.
+ * See the COPYING file in the top-level directory.
  */
 
 #include "trace/control.h"
 
 
-void trace_backend_init_events(const char *fname)
+TraceEvent *trace_event_name(const char *name)
+{
+    assert(name != NULL);
+
+    TraceEventID i;
+    for (i = 0; i < trace_event_count(); i++) {
+        TraceEvent *ev = trace_event_id(i);
+        if (strcmp(trace_event_get_name(ev), name) == 0) {
+            return ev;
+        }
+    }
+    return NULL;
+}
+
+static bool pattern_glob(const char *pat, const char *ev)
+{
+    while (*pat != '\0' && *ev != '\0') {
+        if (*pat == *ev) {
+            pat++;
+            ev++;
+        }
+        else if (*pat == '*') {
+            if (pattern_glob(pat, ev+1)) {
+                return true;
+            } else if (pattern_glob(pat+1, ev)) {
+                return true;
+            } else {
+                return false;
+            }
+        } else {
+            return false;
+        }
+    }
+
+    while (*pat == '*') {
+        pat++;
+    }
+
+    if (*pat == '\0' && *ev == '\0') {
+        return true;
+    } else {
+        return false;
+    }
+}
+
+TraceEvent *trace_event_pattern(const char *pat, TraceEvent *ev)
 {
-    int ret;
+    assert(pat != NULL);
 
+    TraceEventID i;
+
+    if (ev == NULL) {
+        i = -1;
+    } else {
+        i = trace_event_get_id(ev);
+    }
+    i++;
+
+    while (i < trace_event_count()) {
+        TraceEvent *res = trace_event_id(i);
+        if (pattern_glob(pat, trace_event_get_name(res))) {
+            return res;
+        }
+        i++;
+    }
+
+    return NULL;
+}
+
+void trace_backend_init_events(const char *fname)
+{
     if (fname == NULL) {
         return;
     }
@@ -32,15 +99,28 @@ void trace_backend_init_events(const char *fname)
             if ('#' == line_buf[0]) { /* skip commented lines */
                 continue;
             }
-            if ('-' == line_buf[0]) {
-                ret = trace_event_set_state(line_buf+1, false);
+            const bool enable = ('-' != line_buf[0]);
+            char *line_ptr = enable ? line_buf : line_buf + 1;
+            if (trace_event_is_pattern(line_ptr)) {
+                TraceEvent *ev = NULL;
+                while ((ev = trace_event_pattern(line_ptr, ev)) != NULL) {
+                    if (trace_event_get_state_static(ev)) {
+                        trace_event_set_state_dynamic(ev, enable);
+                    }
+                }
             } else {
-                ret = trace_event_set_state(line_buf, true);
-            }
-            if (!ret) {
-                fprintf(stderr,
-                        "error: trace event '%s' does not exist\n", line_buf);
-                exit(1);
+                TraceEvent *ev = trace_event_name(line_ptr);
+                if (ev == NULL) {
+                    fprintf(stderr,
+                            "error: trace event '%s' does not exist\n", line_ptr);
+                    exit(1);
+                }
+                if (!trace_event_get_state_static(ev)) {
+                    fprintf(stderr,
+                            "error: trace event '%s' is not traceable\n", line_ptr);
+                    exit(1);
+                }
+                trace_event_set_state_dynamic(ev, enable);
             }
         }
     }