shared: use NMStrBuf in _nm_utils_enum_to_str_full()th/strbuf-v2

Just for showcase and to hit the code from the unit-tests
that we have.

Also, just to show, the following runs about 25 % faster than before,
which isn't bad for such a simple replacement.

    {
         GType gtype = nm_test_general_color_flags_get_type ();
         const int N_RUN = 1000000;
         int i_run;
         guint8 c = 0;

         for (i_run = 0; i_run < N_RUN; i_run++) {
              gs_free char *str = NULL;

              str = _nm_utils_enum_to_str_full (gtype, i_run % 10, ",", NULL);
              c += str[0];
         }
         return c % 3;
    }

$ perf stat -r 200 -B libnm-core/tests/test-general

Before:

 Performance counter stats for 'libnm-core/tests/test-general' (200 runs):

            204.48 msec task-clock:u              #    0.997 CPUs utilized            ( +-  0.53% )
                 0      context-switches:u        #    0.000 K/sec
                 0      cpu-migrations:u          #    0.000 K/sec
               267      page-faults:u             #    0.001 M/sec                    ( +-  0.05% )
       702,987,494      cycles:u                  #    3.438 GHz                      ( +-  0.54% )
     1,698,874,415      instructions:u            #    2.42  insn per cycle           ( +-  0.00% )
       410,394,229      branches:u                # 2006.970 M/sec                    ( +-  0.00% )
         1,770,484      branch-misses:u           #    0.43% of all branches          ( +-  0.40% )

           0.20502 +- 0.00108 seconds time elapsed  ( +-  0.53% )

After:

 Performance counter stats for 'libnm-core/tests/test-general' (200 runs):

            155.71 msec task-clock:u              #    0.996 CPUs utilized            ( +-  0.50% )
                 0      context-switches:u        #    0.000 K/sec
                 0      cpu-migrations:u          #    0.000 K/sec
               266      page-faults:u             #    0.002 M/sec                    ( +-  0.05% )
       539,994,118      cycles:u                  #    3.468 GHz                      ( +-  0.49% )
     1,116,016,733      instructions:u            #    2.07  insn per cycle           ( +-  0.00% )
       283,974,158      branches:u                # 1823.760 M/sec                    ( +-  0.00% )
         1,377,786      branch-misses:u           #    0.49% of all branches          ( +-  0.43% )

          0.156255 +- 0.000786 seconds time elapsed  ( +-  0.50% )

1 files changed, 13 insertions, 10 deletions

diff --git a/shared/nm-glib-aux/nm-enum-utils.c b/shared/nm-glib-aux/nm-enum-utils.c
index e92797fdd1..854eda6e5a 100644
--- a/shared/nm-glib-aux/nm-enum-utils.c
+++ b/shared/nm-glib-aux/nm-enum-utils.c
@@ -6,6 +6,7 @@
 #include "nm-default.h"
 
 #include "nm-enum-utils.h"
+#include "nm-str-buf.h"
 
 /*****************************************************************************/
 
@@ -142,12 +143,14 @@ _nm_utils_enum_to_str_full (GType type,
 		else
 			return g_strdup (enum_value->value_nick);
 	} else if (G_IS_FLAGS_CLASS (klass)) {
-		GFlagsValue *flags_value;
-		GString *str = g_string_sized_new (16);
 		unsigned uvalue = (unsigned) value;
+		GFlagsValue *flags_value;
+		NMStrBuf strbuf;
 
 		flags_separator = flags_separator ?: " ";
 
+		nm_str_buf_init (&strbuf, 16, FALSE);
+
 		for ( ; value_infos && value_infos->nick; value_infos++) {
 
 			nm_assert (_enum_is_valid_flags_nick (value_infos->nick));
@@ -160,9 +163,9 @@ _nm_utils_enum_to_str_full (GType type,
 					continue;
 			}
 
-			if (str->len)
-				g_string_append (str, flags_separator);
-			g_string_append (str, value_infos->nick);
+			if (strbuf.len)
+				nm_str_buf_append (&strbuf, flags_separator);
+			nm_str_buf_append (&strbuf, value_infos->nick);
 			uvalue &= ~((unsigned) value_infos->value);
 			if (uvalue == 0) {
 				/* we printed all flags. Done. */
@@ -172,20 +175,20 @@ _nm_utils_enum_to_str_full (GType type,
 
 		do {
 			flags_value = g_flags_get_first_value (G_FLAGS_CLASS (klass), uvalue);
-			if (str->len)
-				g_string_append (str, flags_separator);
+			if (strbuf.len)
+				nm_str_buf_append (&strbuf, flags_separator);
 			if (   !flags_value
 			    || !_enum_is_valid_flags_nick (flags_value->value_nick)) {
 				if (uvalue)
-					g_string_append_printf (str, "0x%x", uvalue);
+					nm_str_buf_append_printf (&strbuf, "0x%x", uvalue);
 				break;
 			}
-			g_string_append (str, flags_value->value_nick);
+			nm_str_buf_append (&strbuf, flags_value->value_nick);
 			uvalue &= ~flags_value->value;
 		} while (uvalue);
 
 flags_done:
-		return g_string_free (str, FALSE);
+		return nm_str_buf_finalize (&strbuf, NULL);
 	}
 
 	g_return_val_if_reached (NULL);