[settings] Add fetchf_setting_copy()

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

src/core/settings.c

@@ -726,7 +726,7 @@ int fetch_setting_len ( struct settings *settings, struct setting *setting ) {
 int fetch_setting_copy ( struct settings *settings, struct setting *setting,
 			 void **data ) {
 	int len;
-	int check_len = 0;
+	int check_len;
 
 	/* Avoid returning uninitialised data on error */
 	*data = NULL;
@@ -1028,7 +1028,7 @@ int setting_cmp ( struct setting *a, struct setting *b ) {
  */
 
 /**
- * Fetch and format value of setting
+ * Fetch formatted value of setting
  *
  * @v settings		Settings block, or NULL to search all blocks
  * @v setting		Setting to fetch
@@ -1064,6 +1064,43 @@ int fetchf_setting ( struct settings *settings, struct setting *setting,
 	return ret;
 }
 
+/**
+ * Fetch copy of formatted value of setting
+ *
+ * @v settings		Settings block, or NULL to search all blocks
+ * @v setting		Setting to fetch
+ * @v type		Settings type
+ * @v value		Buffer to allocate and fill with formatted value
+ * @ret len		Length of formatted value, or negative error
+ *
+ * The caller is responsible for eventually freeing the allocated
+ * buffer.
+ */
+int fetchf_setting_copy ( struct settings *settings, struct setting *setting,
+			  char **value ) {
+	int len;
+	int check_len;
+
+	/* Avoid returning uninitialised data on error */
+	*value = NULL;
+
+	/* Check existence, and fetch formatted value length */
+	len = fetchf_setting ( settings, setting, NULL, 0 );
+	if ( len < 0 )
+		return len;
+
+	/* Allocate buffer */
+	*value = zalloc ( len + 1 /* NUL */ );
+	if ( ! *value )
+		return -ENOMEM;
+
+	/* Fetch formatted value */
+	check_len = fetchf_setting ( settings, setting, *value,
+				     ( len + 1 /* NUL */ ) );
+	assert ( check_len == len );
+	return len;
+}
+
 /**
  * Store formatted value of setting
  *

src/include/ipxe/settings.h

@@ -310,6 +310,8 @@ extern int setting_name ( struct settings *settings, struct setting *setting,
 			  char *buf, size_t len );
 extern int fetchf_setting ( struct settings *settings, struct setting *setting,
 			    char *buf, size_t len );
+extern int fetchf_setting_copy ( struct settings *settings,
+				 struct setting *setting, char **value );
 extern int storef_setting ( struct settings *settings,
 			    struct setting *setting,
 			    const char *value );