[settings] Eliminate call to fetchf_named_setting() in expand_settings()

Use parse_setting_name() and fetchf_setting_copy() in
expand_settings(), to eliminate the call to fetchf_named_setting().

This change also eliminates the potentially large stack-allocated
buffer in expand_settings().

Signed-off-by: Michael Brown <mcb30@ipxe.org>

diff --git a/src/core/settings.c b/src/core/settings.c
index d3d15155691e4aee8944eb910627138430111198..d5e02460d16c750207c9347222f127c074dffa00 100644 (file)
--- a/src/core/settings.c
+++ b/src/core/settings.c
@@ -2014,15 +2014,18 @@ struct setting_type setting_type_busdevfn __setting_type = {
  * eventually free() it.
  */
 char * expand_settings ( const char *string ) {
+       struct settings *settings;
+       struct setting setting;
        char *expstr;
        char *start;
        char *end;
        char *head;
        char *name;
        char *tail;
-       int setting_len;
-       int new_len;
+       char *value;
        char *tmp;
+       int new_len;
+       int rc;
 
        /* Obtain temporary modifiable copy of string */
        expstr = strdup ( string );
@@ -2052,27 +2055,27 @@ char * expand_settings ( const char *string ) {
                *end = '\0';
                tail = ( end + 1 );
 
-               /* Determine setting length */
-               setting_len = fetchf_named_setting ( name, NULL, 0, NULL, 0 );
-               if ( setting_len < 0 )
-                       setting_len = 0; /* Treat error as empty setting */
-
-               /* Read setting into temporary buffer */
-               {
-                       char setting_buf[ setting_len + 1 ];
-
-                       setting_buf[0] = '\0';
-                       fetchf_named_setting ( name, NULL, 0, setting_buf,
-                                              sizeof ( setting_buf ) );
-
-                       /* Construct expanded string and discard old string */
-                       tmp = expstr;
-                       new_len = asprintf ( &expstr, "%s%s%s",
-                                            head, setting_buf, tail );
-                       free ( tmp );
-                       if ( new_len < 0 )
-                               return NULL;
+               /* Expand setting */
+               if ( ( rc = parse_setting_name ( name, find_child_settings,
+                                                &settings,
+                                                &setting ) ) != 0 ) {
+                       /* Treat invalid setting names as empty */
+                       value = NULL;
+               } else {
+                       /* Fetch and format setting value.  Ignore
+                        * errors; treat non-existent settings as empty.
+                        */
+                       fetchf_setting_copy ( settings, &setting, &value );
                }
+
+               /* Construct expanded string and discard old string */
+               tmp = expstr;
+               new_len = asprintf ( &expstr, "%s%s%s",
+                                    head, ( value ? value : "" ), tail );
+               free ( value );
+               free ( tmp );
+               if ( new_len < 0 )
+                       return NULL;
        }
 
        return expstr;