[ClusterLabs Developers] libqb: Re: 633f262 logging: Remove linker 'magic' and just use statics for logging callsites (#322)

[Lars Ellenberg]

Back then when this "dynamic" logging was introduced,
I thought the whole point was that "quiet" callsites
are "cheap".

So I think you want to
qb_log_callsite_get() only *once* per callsite,
assign that to a static pointer (as you say in the commit message).
And do the actual qb_log_real_() function call
only conditionally based on if (cs->targets). 

That way, a disabled trace logging boils down to a
if (cs && cs->targets)
    ;
Much cheaper than what you have now.

Or was always calling into both qb_log_callsite_get() and qb_log_real_()
intentional for some obscure (to me) reason,
even for disabled call sites?

Below I also added a test for (cs->tags & QB_LOG_TAG_LIBQB_MSG),
in case someone used qb_util_set_log_function().
If that special tag flag could be folded into cs->targets (e.g. bit 0),
I'd like it even better.

Cheers,
    Lars


diff --git a/include/qb/qblog.h b/include/qb/qblog.h
index 1943b94..f63f4ad 100644
--- a/include/qb/qblog.h
+++ b/include/qb/qblog.h
@@ -485,11 +485,17 @@ void qb_log_from_external_source_va(const char *function,
 	qb_log_real_(&descriptor, ##args);				\
     } while(0)
 #else
-#define qb_logt(priority, tags, fmt, args...) do {	\
-	struct qb_log_callsite* descriptor_pt =		\
-	qb_log_callsite_get(__func__, __FILE__, fmt,	\
-			    priority, __LINE__, tags);	\
-	qb_log_real_(descriptor_pt, ##args);		\
+#define qb_logt(priority, tags, fmt, args...) do {		\
+	static struct qb_log_callsite* descriptor_pt;		\
+	if (!descriptor_pt) {					\
+		descriptor_pt =					\
+		qb_log_callsite_get(__func__, __FILE__, fmt,	\
+				    priority, __LINE__, tags);	\
+	}							\
+	if (descriptor_pt->targets ||				\
+	    qb_bit_is_set(descriptor_pt->tags,			\
+		    QB_LOG_TAG_LIBQB_MSG_BIT))			\
+		qb_log_real_(descriptor_pt, ##args);		\
     } while(0)
 #endif /* QB_HAVE_ATTRIBUTE_SECTION */