MINOR: trace: ensure -dt priority over traces config section

Traces can be activated on startup either via -dt command line argument
or via the traces configuration section. This can caused confusion as it
may not be clear as trace source can be completed or overriden by one or
the other.

Fix the precedence to give the priority to the command line argument.
Now, each trace source configured via -dt is first resetted to a default
state before applying new settings. Then, it is impossible to change a
trace source via the configuration file if it was already targetted via
-dt argument.

include/haproxy/trace-t.h

@@ -184,6 +184,7 @@ struct trace_source {
 	enum trace_state state;
 	const void *lockon_ptr;  // what to lockon when lockon is set
 	const struct trace_source *follow; // other trace source's tracker to follow
+	int cmdline;             // true if source was activated via -dt command line args
 };
 
 #endif /* _HAPROXY_TRACE_T_H */

src/trace.c

@@ -27,6 +27,7 @@
 #include <haproxy/istbuf.h>
 #include <haproxy/list.h>
 #include <haproxy/log.h>
+#include <haproxy/global.h>
 #include <haproxy/quic_conn-t.h>
 #include <haproxy/sink.h>
 #include <haproxy/trace.h>
@@ -348,11 +349,7 @@ void trace_no_cb(enum trace_level level, uint64_t mask, const struct trace_sourc
 	/* do nothing */
 }
 
-/* registers trace source <source>. Modifies the list element!
- * The {start,pause,stop,report} events are not changed so the source may
- * preset them.
- */
-void trace_register_source(struct trace_source *source)
+static void trace_source_reset(struct trace_source *source)
 {
 	source->lockon = TRACE_LOCKON_NOTHING;
 	source->level = TRACE_LEVEL_USER;
@@ -360,6 +357,16 @@ void trace_register_source(struct trace_source *source)
 	source->sink = NULL;
 	source->state = TRACE_STATE_STOPPED;
 	source->lockon_ptr = NULL;
+	source->cmdline = 0;
+}
+
+/* registers trace source <source>. Modifies the list element!
+ * The {start,pause,stop,report} events are not changed so the source may
+ * preset them.
+ */
+void trace_register_source(struct trace_source *source)
+{
+	trace_source_reset(source);
 	LIST_APPEND(&trace_sources, &source->source_link);
 }
 
@@ -473,6 +480,15 @@ static struct sink *_trace_get_sink(const char *name, char **msg,
 	return sink;
 }
 
+/* Returns true if <src> trace source configuration can be changed. */
+static int trace_enforce_origin_priority(const struct trace_source *src)
+{
+	/* Trace cannot be modified via configuration file (during startup) if
+	 * already activated via -dt command line argument.
+	 */
+	return !src->cmdline || !(global.mode & MODE_STARTING);
+}
+
 /* Parse a "trace" statement. Returns a severity as a LOG_* level and a status
  * message that may be delivered to the user, in <msg>. The message will be
  * nulled first and msg must be an allocated pointer. A null status message output
@@ -555,6 +571,9 @@ static int _trace_parse_statement(char **args, char **msg, const char *file, int
 		return LOG_ERR;
 	}
 
+	if (src && !trace_enforce_origin_priority(src))
+		goto out;
+
 	if (strcmp(args[cur_arg], "follow") == 0) {
 		const struct trace_source *origin = src ? HA_ATOMIC_LOAD(&src->follow) : NULL;
 
@@ -589,12 +608,15 @@ static int _trace_parse_statement(char **args, char **msg, const char *file, int
 			}
 		}
 
-		if (src)
+		if (src) {
 			HA_ATOMIC_STORE(&src->follow, origin);
-		else
-			list_for_each_entry(src, &trace_sources, source_link)
-				if (src != origin)
+		}
+		else {
+			list_for_each_entry(src, &trace_sources, source_link) {
+				if (src != origin && trace_enforce_origin_priority(src))
 					HA_ATOMIC_STORE(&src->follow, origin);
+			}
+		}
 		cur_arg += 2;
 		goto next_stmt;
 	}
@@ -712,11 +734,15 @@ static int _trace_parse_statement(char **args, char **msg, const char *file, int
 				return LOG_ERR;
 		}
 
-		if (src)
+		if (src) {
 			HA_ATOMIC_STORE(&src->sink, sink);
-		else
-			list_for_each_entry(src, &trace_sources, source_link)
+		}
+		else {
+			list_for_each_entry(src, &trace_sources, source_link) {
+				if (trace_enforce_origin_priority(src))
 					HA_ATOMIC_STORE(&src->sink, sink);
+			}
+		}
 
 		cur_arg += 2;
 		goto next_stmt;
@@ -750,11 +776,15 @@ static int _trace_parse_statement(char **args, char **msg, const char *file, int
 			return *name ? LOG_ERR : LOG_WARNING;
 		}
 
-		if (src)
+		if (src) {
 			HA_ATOMIC_STORE(&src->level, level);
-		else
-			list_for_each_entry(src, &trace_sources, source_link)
+		}
+		else {
+			list_for_each_entry(src, &trace_sources, source_link) {
+				if (trace_enforce_origin_priority(src))
 					HA_ATOMIC_STORE(&src->level, level);
+			}
+		}
 
 		cur_arg += 2;
 		goto next_stmt;
@@ -960,10 +990,12 @@ static int trace_parse_statement(char **args, char **msg)
 
 void _trace_parse_cmd(struct trace_source *src, int level, int verbosity)
 {
+	trace_source_reset(src);
 	src->sink = sink_find("stderr");
 	src->level = level >= 0 ? level : TRACE_LEVEL_ERROR;
 	src->verbosity = verbosity >= 0 ? verbosity : 1;
 	src->state = TRACE_STATE_RUNNING;
+	src->cmdline = 1;
 }
 
 /* Parse a process argument specified via "-dt".