[Qemu-devel] [PATCH 1/3] log: improve performance of qemu_log and qemu_log_mask if disabled

["Denis V. Lunev" <den@openvz.org>]

The patch is intended to avoid to perform any operation including
calculation of log function arguments when the log is not enabled due to
various reasons.

Functions qemu_log and qemu_log_mask are replaced with variadic macros.
Unfortunately the code is not C99 compatible and we can not use
portable __VA_ARGS__ way. There are a lot of warnings in the other
places with --std=c99. Thus the only way to achive the result is to use
args.. GCC extension.

Format checking performed by compiler will not suffer by this patch. It
will be done inside in fprintf arguments checking.

Signed-off-by: Denis V. Lunev <den@openvz.org>
Signed-off-by: Pavel Butsykin <pbutsykin@virtuozzo.com>
CC: Markus Armbruster <armbru@redhat.com>
CC: Luiz Capitulino <lcapitulino@redhat.com>
CC: Eric Blake <eblake@redhat.com>
CC: Peter Maydell <peter.maydell@linaro.org>
---
 include/qemu/log.h | 17 ++++++++++++++---
 qemu-log.c         | 21 ---------------------
 2 files changed, 14 insertions(+), 24 deletions(-)

diff --git a/include/qemu/log.h b/include/qemu/log.h
index f880e66..57b8c96 100644
--- a/include/qemu/log.h
+++ b/include/qemu/log.h
@@ -53,7 +53,13 @@ static inline bool qemu_loglevel_mask(int mask)
 
 /* main logging function
  */
-void GCC_FMT_ATTR(1, 2) qemu_log(const char *fmt, ...);
+#define qemu_log(args...)                   \
+    do {                                    \
+        if (!qemu_log_enabled()) {          \
+            break;                          \
+        }                                   \
+        fprintf(qemu_logfile, args);        \
+    } while (0)
 
 /* vfprintf-like logging function
  */
@@ -67,8 +73,13 @@ qemu_log_vprintf(const char *fmt, va_list va)
 
 /* log only if a bit is set on the current loglevel mask
  */
-void GCC_FMT_ATTR(2, 3) qemu_log_mask(int mask, const char *fmt, ...);
-
+#define qemu_log_mask(mask, args...)        \
+    do {                                    \
+        if (!qemu_loglevel_mask(mask)) {    \
+            break;                          \
+        }                                   \
+        qemu_log(args);                     \
+    } while (0)
 
 /* Special cases: */
 
diff --git a/qemu-log.c b/qemu-log.c
index 13f3813..e6d2b3f 100644
--- a/qemu-log.c
+++ b/qemu-log.c
@@ -25,27 +25,6 @@ FILE *qemu_logfile;
 int qemu_loglevel;
 static int log_append = 0;
 
-void qemu_log(const char *fmt, ...)
-{
-    va_list ap;
-
-    va_start(ap, fmt);
-    if (qemu_logfile) {
-        vfprintf(qemu_logfile, fmt, ap);
-    }
-    va_end(ap);
-}
-
-void qemu_log_mask(int mask, const char *fmt, ...)
-{
-    va_list ap;
-
-    va_start(ap, fmt);
-    if ((qemu_loglevel & mask) && qemu_logfile) {
-        vfprintf(qemu_logfile, fmt, ap);
-    }
-    va_end(ap);
-}
 
 /* enable or disable low levels log */
 void do_qemu_set_log(int log_flags, bool use_own_buffers)
-- 
2.1.4