talloc: Tune talloc_vasprintf

vsnprintf is significantly more expensive than memcpy. For the
common case where the string we print is less than a kilobyte, avoid
the second vsnprintf.

Signed-off-by: Volker Lendecke <vl@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>
Autobuild-User(master): Jeremy Allison <jra@samba.org>
Autobuild-Date(master): Thu May 15 12:49:14 CEST 2014 on sn-devel-104

(cherry picked from commit 593c8103af5a5ed6b3c915369fed5b90efb42c25)

diff --git a/lib/talloc/talloc.c b/lib/talloc/talloc.c
index 1cb4d7dead792dad9bf362a1fb1025b3f802767d..2a5406e11d02a4667bc30453c883d650b7a95f5d 100644 (file)
--- a/lib/talloc/talloc.c
+++ b/lib/talloc/talloc.c
@@ -2356,11 +2356,11 @@ _PUBLIC_ char *talloc_vasprintf(const void *t, const char *fmt, va_list ap)
        int len;
        char *ret;
        va_list ap2;
-       char c;
+       char buf[1024];
 
        /* this call looks strange, but it makes it work on older solaris boxes */
        va_copy(ap2, ap);
-       len = vsnprintf(&c, 1, fmt, ap2);
+       len = vsnprintf(buf, sizeof(buf), fmt, ap2);
        va_end(ap2);
        if (unlikely(len < 0)) {
                return NULL;
@@ -2369,9 +2369,13 @@ _PUBLIC_ char *talloc_vasprintf(const void *t, const char *fmt, va_list ap)
        ret = (char *)__talloc(t, len+1);
        if (unlikely(!ret)) return NULL;
 
-       va_copy(ap2, ap);
-       vsnprintf(ret, len+1, fmt, ap2);
-       va_end(ap2);
+       if (len < sizeof(buf)) {
+               memcpy(ret, buf, len+1);
+       } else {
+               va_copy(ap2, ap);
+               vsnprintf(ret, len+1, fmt, ap2);
+               va_end(ap2);
+       }
 
        _talloc_set_name_const(ret, ret);
        return ret;