readline(): Add ability to modify a string buffer

If the 'buf' parameter is a non-0-length string, its contents will be
edited.  Previously, the initial contents of 'buf' were ignored and the
user entered its contents from scratch.

This change is necessary to support the upcoming "editenv" command but
could also be used for future commands which require a user to modify
an existing string.

Signed-off-by: Peter Tyser <ptyser@xes-inc.com>

common/main.c

@@ -720,6 +720,10 @@ static int cread_line(const char *const prompt, char *buf, unsigned int *len)
 	int insert = 1;
 	int esc_len = 0;
 	char esc_save[8];
+	int init_len = strlen(buf);
+
+	if (init_len)
+		cread_add_str(buf, init_len, 1, &num, &eol_num, buf, *len);
 
 	while (1) {
 #ifdef CONFIG_BOOT_RETRY_TIME
@@ -937,6 +941,12 @@ static int cread_line(const char *const prompt, char *buf, unsigned int *len)
  */
 int readline (const char *const prompt)
 {
+	/*
+	 * If console_buffer isn't 0-length the user will be prompted to modify
+	 * it instead of entering it from scratch as desired.
+	 */
+	console_buffer[0] = '\0';
+
 	return readline_into_buffer(prompt, console_buffer);
 }