src/common.c: Reimplement format_name for performance.

This is used from uc_update(), i.e. for every value list dispatched, and was
one of the most expensive functions thanks to snprintf().

This reduces total time spent in the format_name() function from 7.78% to 1.89%
during a network stress test.

diff --git a/src/common.c b/src/common.c
index b679bf7..5de7d97 100644 (file)
--- a/src/common.c
+++ b/src/common.c
@@ -664,7 +664,7 @@ long long get_kstat_value (kstat_t *ksp, char *name)
                retval = (long long) kn->value.ui64; /* XXX: Might overflow! */
        else
                WARNING ("get_kstat_value: Not a numeric value: %s", name);
-                
+
        return (retval);
 }
 #endif /* HAVE_LIBKSTAT */
@@ -771,36 +771,43 @@ int format_name (char *ret, int ret_len,
                const char *plugin, const char *plugin_instance,
                const char *type, const char *type_instance)
 {
-       int  status;
+  char *buffer;
+  size_t buffer_size;
+
+  buffer = ret;
+  buffer_size = (size_t) ret_len;
+
+#define APPEND(str) do {                                               \
+  size_t l = strlen (str);                                             \
+  if (l >= buffer_size)                                                \
+    return (ENOBUFS);                                                  \
+  memcpy (buffer, (str), l);                                           \
+  buffer += l; buffer_size -= l;                                       \
+} while (0)
 
-       assert (plugin != NULL);
-       assert (type != NULL);
+  assert (plugin != NULL);
+  assert (type != NULL);
 
-       if ((plugin_instance == NULL) || (strlen (plugin_instance) == 0))
-       {
-               if ((type_instance == NULL) || (strlen (type_instance) == 0))
-                       status = ssnprintf (ret, ret_len, "%s/%s/%s",
-                                       hostname, plugin, type);
-               else
-                       status = ssnprintf (ret, ret_len, "%s/%s/%s-%s",
-                                       hostname, plugin, type,
-                                       type_instance);
-       }
-       else
-       {
-               if ((type_instance == NULL) || (strlen (type_instance) == 0))
-                       status = ssnprintf (ret, ret_len, "%s/%s-%s/%s",
-                                       hostname, plugin, plugin_instance,
-                                       type);
-               else
-                       status = ssnprintf (ret, ret_len, "%s/%s-%s/%s-%s",
-                                       hostname, plugin, plugin_instance,
-                                       type, type_instance);
-       }
+  APPEND (hostname);
+  APPEND ("/");
+  APPEND (plugin);
+  if ((plugin_instance != NULL) && (plugin_instance[0] != 0))
+  {
+    APPEND ("-");
+    APPEND (plugin_instance);
+  }
+  APPEND ("/");
+  APPEND (type);
+  if ((type_instance != NULL) && (type_instance[0] != 0))
+  {
+    APPEND ("-");
+    APPEND (type_instance);
+  }
+  assert (buffer_size > 0);
+  buffer[0] = 0;
 
-       if ((status < 1) || (status >= ret_len))
-               return (-1);
-       return (0);
+#undef APPEND
+  return (0);
 } /* int format_name */
 
 int format_values (char *ret, size_t ret_len, /* {{{ */