trace: don't copy strings where we don't need to.

1. trace_span_start() is always called with a string literal, so
   no copy needed (and we can use a macro to enforce this).
2. trace_span_tag() name and value are always longer-lived than
   the span, so no need to copy these either.

Before:
	real	0m18.524000-19.100000(18.7674+/-0.21)s
	user	0m16.171000-16.833000(16.424+/-0.26)s
	sys	0m2.259000-2.400000(2.337+/-0.059)s

After:
	real	0m16.421000-18.407000(17.8128+/-0.72)s
	user	0m14.242000-16.041000(15.5382+/-0.67)s
	sys	0m2.179000-2.363000(2.273+/-0.061)s

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

Author: rustyrussell

common/trace.c

@@ -68,7 +68,7 @@ struct span {
 	size_t key;
 	struct span *parent;
 	struct span_tag *tags;
-	char *name;
+	const char *name;
 
 	bool suspended;
 	/* Indicate whether this is a remote span, i.e., it was
@@ -94,7 +94,7 @@ static void init_span(struct span *s,
 	s->start_time = (now.ts.tv_sec * 1000000) + now.ts.tv_nsec / 1000;
 	s->parent = parent;
 	s->tags = notleak(tal_arr(NULL, struct span_tag, 0));
-	s->name = notleak(tal_strdup(NULL, name));
+	s->name = name;
 	s->suspended = false;
 
 	/* If this is a new root span we also need to associate a new
@@ -308,13 +308,13 @@ static void trace_span_clear(struct span *s)
 	s->key = 0;
 	memset(s->id, 0, SPAN_ID_SIZE);
 	memset(s->trace_id, 0, TRACE_ID_SIZE);
-	;
+
 	s->parent = NULL;
-	s->name = tal_free(s->name);
+	s->name = NULL;
 	s->tags = tal_free(s->tags);
 }
 
-void trace_span_start(const char *name, const void *key)
+void trace_span_start_(const char *name, const void *key)
 {
 	size_t numkey = trace_key(key);
 
@@ -380,6 +380,7 @@ void trace_span_tag(const void *key, const char *name, const char *value)
 	if (disable_trace)
 		return;
 
+	assert(name);
 	size_t numkey = trace_key(key);
 	struct span *span = trace_span_find(numkey);
 	assert(span);
@@ -468,7 +469,7 @@ void trace_cleanup(void)
 
 #else /* HAVE_USDT */
 
-void trace_span_start(const char *name, const void *key) {}
+void trace_span_start_(const char *name, const void *key) {}
 void trace_span_end(const void *key) {}
 void trace_span_suspend_(const void *key, const char *lbl) {}
 void trace_span_suspend_may_free_(const void *key, const char *lbl) {}

common/trace.h

@@ -7,7 +7,9 @@
 #define TRACE_ID_SIZE 16
 #undef TRACE_DEBUG
 
-void trace_span_start(const char *name, const void *key);
+/* name must be a string constant */
+#define trace_span_start(name, key) trace_span_start_(name "", (key))
+void trace_span_start_(const char *name, const void *key);
 void trace_span_end(const void *key);
 void trace_span_tag(const void *key, const char *name, const char *value);
 void trace_cleanup(void);

lightningd/test/run-find_my_abspath.c

@@ -269,9 +269,9 @@ void trace_span_end(const void *key UNNEEDED)
 /* Generated stub for trace_span_resume_ */
 void trace_span_resume_(const void *key UNNEEDED, const char *lbl UNNEEDED)
 { fprintf(stderr, "trace_span_resume_ called!\n"); abort(); }
-/* Generated stub for trace_span_start */
-void trace_span_start(const char *name UNNEEDED, const void *key UNNEEDED)
-{ fprintf(stderr, "trace_span_start called!\n"); abort(); }
+/* Generated stub for trace_span_start_ */
+void trace_span_start_(const char *name UNNEEDED, const void *key UNNEEDED)
+{ fprintf(stderr, "trace_span_start_ called!\n"); abort(); }
 /* Generated stub for txfilter_add_derkey */
 void txfilter_add_derkey(struct txfilter *filter UNNEEDED,
 			 const u8 derkey[PUBKEY_CMPR_LEN])

lightningd/test/run-jsonrpc.c

@@ -176,9 +176,9 @@ void towire_node_id(u8 **pptr UNNEEDED, const struct node_id *id UNNEEDED)
 /* Generated stub for trace_span_end */
 void trace_span_end(const void *key UNNEEDED)
 { fprintf(stderr, "trace_span_end called!\n"); abort(); }
-/* Generated stub for trace_span_start */
-void trace_span_start(const char *name UNNEEDED, const void *key UNNEEDED)
-{ fprintf(stderr, "trace_span_start called!\n"); abort(); }
+/* Generated stub for trace_span_start_ */
+void trace_span_start_(const char *name UNNEEDED, const void *key UNNEEDED)
+{ fprintf(stderr, "trace_span_start_ called!\n"); abort(); }
 /* Generated stub for trace_span_tag */
 void trace_span_tag(const void *key UNNEEDED, const char *name UNNEEDED, const char *value UNNEEDED)
 { fprintf(stderr, "trace_span_tag called!\n"); abort(); }

plugins/test/run-route-calc.c

@@ -326,9 +326,9 @@ void towire_channel_id(u8 **pptr UNNEEDED, const struct channel_id *channel_id U
 /* Generated stub for trace_span_end */
 void trace_span_end(const void *key UNNEEDED)
 { fprintf(stderr, "trace_span_end called!\n"); abort(); }
-/* Generated stub for trace_span_start */
-void trace_span_start(const char *name UNNEEDED, const void *key UNNEEDED)
-{ fprintf(stderr, "trace_span_start called!\n"); abort(); }
+/* Generated stub for trace_span_start_ */
+void trace_span_start_(const char *name UNNEEDED, const void *key UNNEEDED)
+{ fprintf(stderr, "trace_span_start_ called!\n"); abort(); }
 /* Generated stub for trace_span_tag */
 void trace_span_tag(const void *key UNNEEDED, const char *name UNNEEDED, const char *value UNNEEDED)
 { fprintf(stderr, "trace_span_tag called!\n"); abort(); }

plugins/test/run-route-overlong.c

@@ -323,9 +323,9 @@ void towire_channel_id(u8 **pptr UNNEEDED, const struct channel_id *channel_id U
 /* Generated stub for trace_span_end */
 void trace_span_end(const void *key UNNEEDED)
 { fprintf(stderr, "trace_span_end called!\n"); abort(); }
-/* Generated stub for trace_span_start */
-void trace_span_start(const char *name UNNEEDED, const void *key UNNEEDED)
-{ fprintf(stderr, "trace_span_start called!\n"); abort(); }
+/* Generated stub for trace_span_start_ */
+void trace_span_start_(const char *name UNNEEDED, const void *key UNNEEDED)
+{ fprintf(stderr, "trace_span_start_ called!\n"); abort(); }
 /* Generated stub for trace_span_tag */
 void trace_span_tag(const void *key UNNEEDED, const char *name UNNEEDED, const char *value UNNEEDED)
 { fprintf(stderr, "trace_span_tag called!\n"); abort(); }