trace: always compile support for controlling and querying trace event states

The current interface is generic for this small set of operations, and thus
other backends can easily modify the "trace/control.c" file to add their own
implementation.
Signed-off-by: NLluís Vilanova <vilanova@ac.upc.edu>

docs/tracing.txt

@@ -108,6 +108,36 @@ portability macros, ensure they are preceded and followed by double quotes:
    of trace events.  Marking trace events disabled by default saves the user
    from having to manually disable noisy trace events.
 
+== Generic interface and monitor commands ==
+
+You can programmatically query and control the dynamic state of trace events
+through a backend-agnostic interface:
+
+* trace_print_events
+
+* 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:
+
+* 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.
+
 == Trace backends ==
 
 The "tracetool" script automates tedious trace event code generation and also
@@ -157,27 +187,9 @@ unless you have specific needs for more advanced backends.
   flushed and emptied.  This means the 'info trace' will display few or no
   entries if the buffer has just been flushed.
 
-* 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.
-
 * trace-file on|off|flush|set <path>
   Enable/disable/flush the trace file or set the trace file name.
 
-==== Enabling/disabling trace events programmatically ====
-
-The st_change_trace_event_state() function can be used to enable or disable trace
-events at runtime inside QEMU:
-
-    #include "trace.h"
-    
-    st_change_trace_event_state("virtio_irq", true); /* enable */
-    [...]
-    st_change_trace_event_state("virtio_irq", false); /* disable */
-
 ==== Analyzing trace files ====
 
 The "simple" backend produces binary trace files that can be formatted with the

hmp-commands.hx

@@ -180,7 +180,6 @@ STEXI
 Output logs to @var{filename}.
 ETEXI
 
-#ifdef CONFIG_TRACE_SIMPLE
     {
         .name       = "trace-event",
         .args_type  = "name:s,option:b",
@@ -195,6 +194,7 @@ STEXI
 changes status of a trace event
 ETEXI
 
+#if defined(CONFIG_SIMPLE_TRACE)
     {
         .name       = "trace-file",
         .args_type  = "op:s?,arg:F?",
@@ -1358,10 +1358,13 @@ ETEXI
 STEXI
 @item info trace
 show contents of trace buffer
+ETEXI
+#endif
+
+STEXI
 @item info trace-events
 show available trace events and their state
 ETEXI
-#endif
 
 STEXI
 @end table

monitor.c

@@ -57,8 +57,9 @@
 #include "json-parser.h"
 #include "osdep.h"
 #include "cpu.h"
+#include "trace/control.h"
 #ifdef CONFIG_TRACE_SIMPLE
-#include "trace.h"
+#include "trace/simple.h"
 #endif
 #include "trace/control.h"
 #include "ui/qemu-spice.h"
@@ -593,7 +594,6 @@ static void do_help_cmd(Monitor *mon, const QDict *qdict)
     help_cmd(mon, qdict_get_try_str(qdict, "name"));
 }
 
-#ifdef CONFIG_TRACE_SIMPLE
 static void do_trace_event_set_state(Monitor *mon, const QDict *qdict)
 {
     const char *tp_name = qdict_get_str(qdict, "name");
@@ -605,6 +605,7 @@ static void do_trace_event_set_state(Monitor *mon, const QDict *qdict)
     }
 }
 
+#ifdef CONFIG_SIMPLE_TRACE
 static void do_trace_file(Monitor *mon, const QDict *qdict)
 {
     const char *op = qdict_get_try_str(qdict, "op");
@@ -1002,12 +1003,12 @@ static void do_info_trace(Monitor *mon)
 {
     st_print_trace((FILE *)mon, &monitor_fprintf);
 }
+#endif
 
 static void do_trace_print_events(Monitor *mon)
 {
     trace_print_events((FILE *)mon, &monitor_fprintf);
 }
-#endif
 
 /**
  * do_quit(): Quit QEMU execution
@@ -3144,6 +3145,7 @@ static const mon_cmd_t info_cmds[] = {
         .help       = "show current contents of trace buffer",
         .mhandler.info = do_info_trace,
     },
+#endif
     {
         .name       = "trace-events",
         .args_type  = "",
@@ -3151,7 +3153,6 @@ static const mon_cmd_t info_cmds[] = {
         .help       = "show available trace-events & their state",
         .mhandler.info = do_trace_print_events,
     },
-#endif
     {
         .name       = NULL,
     },