[hci] Use dynamically allocated buffers for editable strings

Editable strings currently require a fixed-size buffer, which is
inelegant and limits the potential for creating interactive forms with
a variable number of edit box widgets.

Remove this limitation by switching to using a dynamically allocated
buffer for editable strings and edit box widgets.

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

8 files changed, 199 insertions, 142 deletions

diff --git a/src/hci/editstring.c b/src/hci/editstring.c
index 8cbce07..b83916c 100644
--- a/src/hci/editstring.c
+++ b/src/hci/editstring.c
@@ -24,8 +24,10 @@
 FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
 
 #include <assert.h>
+#include <errno.h>
 #include <string.h>
 #include <ctype.h>
+#include <stdlib.h>
 #include <ipxe/keys.h>
 #include <ipxe/editstring.h>
 
@@ -35,17 +37,17 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
  *
  */
 
-static void insert_delete ( struct edit_string *string, size_t delete_len,
-                            const char *insert_text ) 
-			    __attribute__ (( nonnull (1) ));
-static void insert_character ( struct edit_string *string,
-                               unsigned int character ) __nonnull;
-static void delete_character ( struct edit_string *string ) __nonnull;
-static void backspace ( struct edit_string *string ) __nonnull;
-static void previous_word ( struct edit_string *string ) __nonnull;
-static void kill_word ( struct edit_string *string ) __nonnull;
-static void kill_sol ( struct edit_string *string ) __nonnull;
-static void kill_eol ( struct edit_string *string ) __nonnull;
+static __attribute__ (( nonnull ( 1 ) )) int
+insert_delete ( struct edit_string *string, size_t delete_len,
+		const char *insert_text );
+static __nonnull int insert_character ( struct edit_string *string,
+					unsigned int character );
+static __nonnull void delete_character ( struct edit_string *string );
+static __nonnull void backspace ( struct edit_string *string );
+static __nonnull void previous_word ( struct edit_string *string );
+static __nonnull void kill_word ( struct edit_string *string );
+static __nonnull void kill_sol ( struct edit_string *string );
+static __nonnull void kill_eol ( struct edit_string *string );
 
 /**
  * Insert and/or delete text within an editable string
@@ -53,35 +55,56 @@ static void kill_eol ( struct edit_string *string ) __nonnull;
  * @v string		Editable string
  * @v delete_len	Length of text to delete from current cursor position
  * @v insert_text	Text to insert at current cursor position, or NULL
+ * @ret rc		Return status code
  */
-static void insert_delete ( struct edit_string *string, size_t delete_len,
-			    const char *insert_text ) {
-	size_t old_len, max_delete_len, insert_len, max_insert_len, new_len;
+static int insert_delete ( struct edit_string *string, size_t delete_len,
+			   const char *insert_text ) {
+	size_t old_len, max_delete_len, insert_len, new_len;
+	char *buf;
+	char *tmp;
 
 	/* Calculate lengths */
-	old_len = strlen ( string->buf );
+	buf = *(string->buf);
+	old_len = ( buf ? strlen ( buf ) : 0 );
 	assert ( string->cursor <= old_len );
 	max_delete_len = ( old_len - string->cursor );
 	if ( delete_len > max_delete_len )
 		delete_len = max_delete_len;
 	insert_len = ( insert_text ? strlen ( insert_text ) : 0 );
-	max_insert_len = ( ( string->len - 1 ) - ( old_len - delete_len ) );
-	if ( insert_len > max_insert_len )
-		insert_len = max_insert_len;
 	new_len = ( old_len - delete_len + insert_len );
 
+	/* Reallocate string, ignoring failures if shrinking */
+	tmp = realloc ( buf, ( new_len + 1 /* NUL */ ) );
+	if ( tmp ) {
+		buf = tmp;
+		*(string->buf) = buf;
+	} else if ( new_len > old_len ) {
+		return -ENOMEM;
+	}
+
 	/* Fill in edit history */
 	string->mod_start = string->cursor;
 	string->mod_end = ( ( new_len > old_len ) ? new_len : old_len );
 
 	/* Move data following the cursor */
-	memmove ( ( string->buf + string->cursor + insert_len ),
-		  ( string->buf + string->cursor + delete_len ),
-		  ( max_delete_len + 1 - delete_len ) );
+	memmove ( ( buf + string->cursor + insert_len ),
+		  ( buf + string->cursor + delete_len ),
+		  ( max_delete_len - delete_len ) );
 
 	/* Copy inserted text to cursor position */
-	memcpy ( ( string->buf + string->cursor ), insert_text, insert_len );
+	memcpy ( ( buf + string->cursor ), insert_text, insert_len );
 	string->cursor += insert_len;
+
+	/* Terminate string (if not NULL) */
+	if ( buf ) {
+		buf[new_len] = '\0';
+	} else {
+		assert ( old_len == 0 );
+		assert ( insert_len == 0 );
+		assert ( new_len == 0 );
+	}
+
+	return 0;
 }
 
 /**
@@ -89,11 +112,13 @@ static void insert_delete ( struct edit_string *string, size_t delete_len,
  *
  * @v string		Editable string
  * @v character		Character to insert
+ * @ret rc		Return status code
  */
-static void insert_character ( struct edit_string *string,
+static int insert_character ( struct edit_string *string,
 			      unsigned int character ) {
 	char insert_text[2] = { character, '\0' };
-	insert_delete ( string, 0, insert_text );
+
+	return insert_delete ( string, 0, insert_text );
 }
 
 /**
@@ -102,7 +127,10 @@ static void insert_character ( struct edit_string *string,
  * @v string		Editable string
  */
 static void delete_character ( struct edit_string *string ) {
-	insert_delete ( string, 1, NULL );
+	int rc;
+
+	rc = insert_delete ( string, 1, NULL );
+	assert ( ( rc == 0 ) || ( *(string->buf) == NULL ) );
 }
 
 /**
@@ -111,6 +139,7 @@ static void delete_character ( struct edit_string *string ) {
  * @v string		Editable string
  */
 static void backspace ( struct edit_string *string ) {
+
 	if ( string->cursor > 0 ) {
 		string->cursor--;
 		delete_character ( string );
@@ -123,14 +152,16 @@ static void backspace ( struct edit_string *string ) {
  * @v string		Editable string
  */
 static void previous_word ( struct edit_string *string ) {
-	while ( string->cursor &&
-		isspace ( string->buf[ string->cursor - 1 ] ) ) {
-		string->cursor--;
+	const char *buf = *(string->buf);
+	size_t cursor = string->cursor;
+
+	while ( cursor && isspace ( buf[ cursor - 1 ] ) ) {
+		cursor--;
 	}
-	while ( string->cursor &&
-		( ! isspace ( string->buf[ string->cursor - 1 ] ) ) ) {
-		string->cursor--;
+	while ( cursor && ( ! isspace ( buf[ cursor - 1 ] ) ) ) {
+		cursor--;
 	}
+	string->cursor = cursor;
 }
 
 /**
@@ -140,8 +171,11 @@ static void previous_word ( struct edit_string *string ) {
  */
 static void kill_word ( struct edit_string *string ) {
 	size_t old_cursor = string->cursor;
+	int rc;
+
 	previous_word ( string );
-	insert_delete ( string, ( old_cursor - string->cursor ), NULL );
+	rc = insert_delete ( string, ( old_cursor - string->cursor ), NULL );
+	assert ( ( rc == 0 ) || ( *(string->buf) == NULL ) );
 }
 
 /**
@@ -151,8 +185,11 @@ static void kill_word ( struct edit_string *string ) {
  */
 static void kill_sol ( struct edit_string *string ) {
 	size_t old_cursor = string->cursor;
+	int rc;
+
 	string->cursor = 0;
-	insert_delete ( string, old_cursor, NULL );
+	rc = insert_delete ( string, old_cursor, NULL );
+	assert ( ( rc == 0 ) || ( *(string->buf) == NULL ) );
 }
 
 /**
@@ -161,18 +198,36 @@ static void kill_sol ( struct edit_string *string ) {
  * @v string		Editable string
  */
 static void kill_eol ( struct edit_string *string ) {
-	insert_delete ( string, ~( ( size_t ) 0 ), NULL );
+	int rc;
+
+	rc = insert_delete ( string, ~( ( size_t ) 0 ), NULL );
+	assert ( ( rc == 0 ) || ( *(string->buf) == NULL ) );
 }
 
 /**
  * Replace editable string
  *
  * @v string		Editable string
- * @v replacement	Replacement string
+ * @v replacement	Replacement string, or NULL to empty the string
+ * @ret rc		Return status code
+ *
+ * Replace the entire content of the editable string and update the
+ * edit history to allow the caller to bring the display into sync
+ * with the string content.
+ *
+ * This function does not itself update the display in any way.
+ *
+ * Upon success, the string buffer is guaranteed to be non-NULL (even
+ * if the replacement string is NULL or empty).
+ *
+ * Errors may safely be ignored if it is deemed that subsequently
+ * failing to update the display will provide sufficient feedback to
+ * the user.
  */
-void replace_string ( struct edit_string *string, const char *replacement ) {
+int replace_string ( struct edit_string *string, const char *replacement ) {
+
 	string->cursor = 0;
-	insert_delete ( string, ~( ( size_t ) 0 ), replacement );
+	return insert_delete ( string, ~( ( size_t ) 0 ), replacement );
 }
 
 /**
@@ -180,21 +235,26 @@ void replace_string ( struct edit_string *string, const char *replacement ) {
  *
  * @v string		Editable string
  * @v key		Key pressed by user
- * @ret key		Key returned to application, or zero
+ * @ret key		Key returned to application, zero, or negative error
  *
  * Handles keypresses and updates the content of the editable string.
  * Basic line editing facilities (delete/insert/cursor) are supported.
  * If edit_string() understands and uses the keypress it will return
  * zero, otherwise it will return the original key.
  *
- * This function does not update the display in any way.
- *
  * The string's edit history will be updated to allow the caller to
  * efficiently bring the display into sync with the string content.
+ *
+ * This function does not itself update the display in any way.
+ *
+ * Errors may safely be ignored if it is deemed that subsequently
+ * failing to update the display will provide sufficient feedback to
+ * the user.
  */
 int edit_string ( struct edit_string *string, int key ) {
+	const char *buf = *(string->buf);
+	size_t len = ( buf ? strlen ( buf ) : 0 );
 	int retval = 0;
-	size_t len = strlen ( string->buf );
 
 	/* Prepare edit history */
 	string->last_cursor = string->cursor;
@@ -204,7 +264,7 @@ int edit_string ( struct edit_string *string, int key ) {
 	/* Interpret key */
 	if ( ( key >= 0x20 ) && ( key <= 0x7e ) ) {
 		/* Printable character; insert at current position */
-		insert_character ( string, key );
+		retval = insert_character ( string, key );
 	} else switch ( key ) {
 	case KEY_BACKSPACE:
 		/* Backspace */
diff --git a/src/hci/mucurses/widgets/editbox.c b/src/hci/mucurses/widgets/editbox.c
index 210de44..fddd274 100644
--- a/src/hci/mucurses/widgets/editbox.c
+++ b/src/hci/mucurses/widgets/editbox.c
@@ -39,20 +39,19 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
  * Initialise text box widget
  *
  * @v box		Editable text box widget
- * @v buf		Text buffer
- * @v len		Size of text buffer
+ * @v buf		Dynamically allocated string buffer
  * @v win		Containing window
  * @v row		Row
  * @v col		Starting column
  * @v width		Width
  * @v flags		Flags
  */
-void init_editbox ( struct edit_box *box, char *buf, size_t len,
+void init_editbox ( struct edit_box *box, char **buf,
 		    WINDOW *win, unsigned int row, unsigned int col,
 		    unsigned int width, unsigned int flags ) {
 	memset ( box, 0, sizeof ( *box ) );
-	init_editstring ( &box->string, buf, len );
-	box->string.cursor = strlen ( buf );
+	init_editstring ( &box->string, buf );
+	box->string.cursor = ( *buf ? strlen ( *buf ) : 0 );
 	box->win = ( win ? win : stdscr );
 	box->row = row;
 	box->col = col;
@@ -67,6 +66,7 @@ void init_editbox ( struct edit_box *box, char *buf, size_t len,
  *
  */
 void draw_editbox ( struct edit_box *box ) {
+	const char *content = *(box->string.buf);
 	size_t width = box->width;
 	char buf[ width + 1 ];
 	signed int cursor_offset, underflow, overflow, first;
@@ -90,13 +90,13 @@ void draw_editbox ( struct edit_box *box ) {
 	/* Construct underscore-padded string portion */
 	memset ( buf, '_', width );
 	buf[width] = '\0';
-	len = ( strlen ( box->string.buf ) - first );
+	len = ( content ? ( strlen ( content ) - first ) : 0 );
 	if ( len > width )
 		len = width;
 	if ( box->flags & EDITBOX_STARS ) {
 		memset ( buf, '*', len );
 	} else {
-		memcpy ( buf, ( box->string.buf + first ), len );
+		memcpy ( buf, ( content + first ), len );
 	}
 
 	/* Print box content and move cursor */
diff --git a/src/hci/readline.c b/src/hci/readline.c
index ecc72d4..5b46413 100644
--- a/src/hci/readline.c
+++ b/src/hci/readline.c
@@ -38,8 +38,6 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
  *
  */
 
-#define READLINE_MAX 1024
-
 /**
  * Synchronise console with edited string
  *
@@ -49,7 +47,8 @@ static void sync_console ( struct edit_string *string ) {
 	unsigned int mod_start = string->mod_start;
 	unsigned int mod_end = string->mod_end;
 	unsigned int cursor = string->last_cursor;
-	size_t len = strlen ( string->buf );
+	const char *buf = *(string->buf);
+	size_t len = strlen ( buf );
 
 	/* Expand region back to old cursor position if applicable */
 	if ( mod_start > string->last_cursor )
@@ -67,7 +66,7 @@ static void sync_console ( struct edit_string *string ) {
 
 	/* Print modified region */
 	while ( cursor < mod_end ) {
-		putchar ( ( cursor >= len ) ? ' ' : string->buf[cursor] );
+		putchar ( ( cursor >= len ) ? ' ' : buf[cursor] );
 		cursor++;
 	}
 
@@ -259,15 +258,11 @@ int readline_history ( const char *prompt, const char *prefill,
 		       struct readline_history *history, unsigned long timeout,
 		       char **line ) {
 	struct edit_string string;
-	char *buf;
 	int key;
 	int move_by;
 	const char *new_string;
 	int rc;
 
-	/* Avoid returning uninitialised data on error */
-	*line = NULL;
-
 	/* Display prompt, if applicable */
 	if ( prompt )
 		printf ( "%s", prompt );
@@ -275,20 +270,15 @@ int readline_history ( const char *prompt, const char *prefill,
 	/* Ensure cursor is visible */
 	printf ( "\033[?25h" );
 
-	/* Allocate buffer and initialise editable string */
-	buf = zalloc ( READLINE_MAX );
-	if ( ! buf ) {
-		rc = -ENOMEM;
-		goto done;
-	}
+	/* Initialise editable string */
+	*line = NULL;
 	memset ( &string, 0, sizeof ( string ) );
-	init_editstring ( &string, buf, READLINE_MAX );
+	init_editstring ( &string, line );
 
-	/* Prefill string, if applicable */
-	if ( prefill ) {
-		replace_string ( &string, prefill );
-		sync_console ( &string );
-	}
+	/* Prefill string */
+	if ( ( rc = replace_string ( &string, prefill ) ) != 0 )
+		goto error;
+	sync_console ( &string );
 
 	while ( 1 ) {
 
@@ -296,7 +286,7 @@ int readline_history ( const char *prompt, const char *prefill,
 		key = getkey ( timeout );
 		if ( key < 0 ) {
 			rc = -ETIMEDOUT;
-			goto done;
+			goto error;
 		}
 		timeout = 0;
 
@@ -307,17 +297,11 @@ int readline_history ( const char *prompt, const char *prefill,
 		switch ( key ) {
 		case CR:
 		case LF:
-			/* Shrink string (ignoring failures) */
-			*line = realloc ( buf,
-					  ( strlen ( buf ) + 1 /* NUL */ ) );
-			if ( ! *line )
-				*line = buf;
-			buf = NULL;
 			rc = 0;
 			goto done;
 		case CTRL_C:
 			rc = -ECANCELED;
-			goto done;
+			goto error;
 		case KEY_UP:
 			move_by = 1;
 			break;
@@ -325,13 +309,13 @@ int readline_history ( const char *prompt, const char *prefill,
 			move_by = -1;
 			break;
 		default:
-			/* Do nothing */
+			/* Do nothing for unrecognised keys or edit errors */
 			break;
 		}
 
 		/* Handle history movement, if applicable */
 		if ( move_by && history ) {
-			new_string = history_move ( history, move_by, buf );
+			new_string = history_move ( history, move_by, *line );
 			if ( new_string ) {
 				replace_string ( &string, new_string );
 				sync_console ( &string );
@@ -339,9 +323,11 @@ int readline_history ( const char *prompt, const char *prefill,
 		}
 	}
 
+ error:
+	free ( *line );
+	*line = NULL;
  done:
 	putchar ( '\n' );
-	free ( buf );
 	if ( history ) {
 		if ( *line && (*line)[0] )
 			history_append ( history, *line );
diff --git a/src/hci/tui/login_ui.c b/src/hci/tui/login_ui.c
index 3c55325..bd24991 100644
--- a/src/hci/tui/login_ui.c
+++ b/src/hci/tui/login_ui.c
@@ -30,6 +30,7 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
  */
 
 #include <string.h>
+#include <stdlib.h>
 #include <errno.h>
 #include <curses.h>
 #include <ipxe/console.h>
@@ -49,8 +50,8 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
 #define EDITBOX_WIDTH		20U
 
 int login_ui ( void ) {
-	char username[64];
-	char password[64];
+	char *username;
+	char *password;
 	struct edit_box username_box;
 	struct edit_box password_box;
 	struct edit_box *current_box = &username_box;
@@ -58,19 +59,16 @@ int login_ui ( void ) {
 	int rc = -EINPROGRESS;
 
 	/* Fetch current setting values */
-	fetch_string_setting ( NULL, &username_setting, username,
-			       sizeof ( username ) );
-	fetch_string_setting ( NULL, &password_setting, password,
-			       sizeof ( password ) );
+	fetchf_setting_copy ( NULL, &username_setting, NULL, NULL, &username );
+	fetchf_setting_copy ( NULL, &password_setting, NULL, NULL, &password );
 
 	/* Initialise UI */
 	initscr();
 	start_color();
-	init_editbox ( &username_box, username, sizeof ( username ), NULL,
-		       USERNAME_ROW, EDITBOX_COL, EDITBOX_WIDTH, 0 );
-	init_editbox ( &password_box, password, sizeof ( password ), NULL,
-		       PASSWORD_ROW, EDITBOX_COL, EDITBOX_WIDTH,
-		       EDITBOX_STARS );
+	init_editbox ( &username_box, &username, NULL, USERNAME_ROW,
+		       EDITBOX_COL, EDITBOX_WIDTH, 0 );
+	init_editbox ( &password_box, &password, NULL, PASSWORD_ROW,
+		       EDITBOX_COL, EDITBOX_WIDTH, EDITBOX_STARS );
 
 	/* Draw initial UI */
 	color_set ( CPAIR_NORMAL, NULL );
@@ -122,16 +120,15 @@ int login_ui ( void ) {
 	erase();
 	endwin();
 
-	if ( rc != 0 )
-		return rc;
+	/* Store settings on successful completion */
+	if ( rc == 0 )
+		rc = storef_setting ( NULL, &username_setting, username );
+	if ( rc == 0 )
+		rc = storef_setting ( NULL, &password_setting, password );
 
-	/* Store settings */
-	if ( ( rc = store_setting ( NULL, &username_setting, username,
-				    strlen ( username ) ) ) != 0 )
-		return rc;
-	if ( ( rc = store_setting ( NULL, &password_setting, password,
-				    strlen ( password ) ) ) != 0 )
-		return rc;
+	/* Free setting values */
+	free ( username );
+	free ( password );
 
-	return 0;
+	return rc;
 }
diff --git a/src/hci/tui/settings_ui.c b/src/hci/tui/settings_ui.c
index be421cc..95cbd77 100644
--- a/src/hci/tui/settings_ui.c
+++ b/src/hci/tui/settings_ui.c
@@ -25,6 +25,7 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
 
 #include <stdio.h>
 #include <stdarg.h>
+#include <stdlib.h>
 #include <unistd.h>
 #include <string.h>
 #include <curses.h>
@@ -58,12 +59,15 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
 	char start[0];							\
 	char pad1[1];							\
 	union {								\
-		char settings[ cols - 1 - 1 - 1 - 1 ];			\
+		struct {						\
+			char name[ cols - 1 - 1 - 1 - 1 - 1 ];		\
+			char pad2[1];					\
+		} __attribute__ (( packed )) settings;			\
 		struct {						\
 			char name[15];					\
 			char pad2[1];					\
 			char value[ cols - 1 - 15 - 1 - 1 - 1 - 1 ];	\
-		} setting;						\
+		} __attribute__ (( packed )) setting;			\
 	} u;								\
 	char pad3[1];							\
 	char nul;							\
@@ -92,8 +96,8 @@ struct settings_ui_row {
 	struct edit_box editbox;
 	/** Editing in progress flag */
 	int editing;
-	/** Buffer for setting's value */
-	char value[256]; /* enough size for a DHCP string */
+	/** Dynamically allocated buffer for setting's value */
+	char *buf;
 };
 
 /** A settings user interface */
@@ -121,24 +125,22 @@ static unsigned int select_setting_row ( struct settings_ui *ui,
 	struct setting *previous = NULL;
 	unsigned int count = 0;
 
+	/* Free any previous setting value */
+	free ( ui->row.buf );
+	ui->row.buf = NULL;
+
 	/* Initialise structure */
 	memset ( &ui->row, 0, sizeof ( ui->row ) );
 	ui->row.row = ( SETTINGS_LIST_ROW + index - ui->scroll.first );
 
 	/* Include parent settings block, if applicable */
-	if ( ui->settings->parent && ( count++ == index ) ) {
+	if ( ui->settings->parent && ( count++ == index ) )
 		ui->row.settings = ui->settings->parent;
-		snprintf ( ui->row.value, sizeof ( ui->row.value ),
-			   "../" );
-	}
 
 	/* Include any child settings blocks, if applicable */
 	list_for_each_entry ( settings, &ui->settings->children, siblings ) {
-		if ( count++ == index ) {
+		if ( count++ == index )
 			ui->row.settings = settings;
-			snprintf ( ui->row.value, sizeof ( ui->row.value ),
-				   "%s/", settings->name );
-		}
 	}
 
 	/* Include any applicable settings */
@@ -155,15 +157,14 @@ static unsigned int select_setting_row ( struct settings_ui *ui,
 
 		/* Read current setting value and origin */
 		if ( count++ == index ) {
-			fetchf_setting ( ui->settings, setting, &ui->row.origin,
-					 &ui->row.setting, ui->row.value,
-					 sizeof ( ui->row.value ) );
+			fetchf_setting_copy ( ui->settings, setting,
+					      &ui->row.origin,
+					      &ui->row.setting, &ui->row.buf );
 		}
 	}
 
 	/* Initialise edit box */
-	init_editbox ( &ui->row.editbox, ui->row.value,
-		       sizeof ( ui->row.value ), NULL, ui->row.row,
+	init_editbox ( &ui->row.editbox, &ui->row.buf, NULL, ui->row.row,
 		       ( SETTINGS_LIST_COL +
 			 offsetof ( typeof ( *text ), u.setting.value ) ),
 		       sizeof ( text->u.setting.value ), 0 );
@@ -197,7 +198,7 @@ static size_t string_copy ( char *dest, const char *src, size_t len ) {
 static void draw_setting_row ( struct settings_ui *ui ) {
 	SETTING_ROW_TEXT ( COLS ) text;
 	unsigned int curs_offset;
-	char *value;
+	const char *value;
 
 	/* Fill row with spaces */
 	memset ( &text, ' ', sizeof ( text ) );
@@ -207,10 +208,12 @@ static void draw_setting_row ( struct settings_ui *ui ) {
 	if ( ui->row.settings ) {
 
 		/* Construct space-padded name */
-		curs_offset = ( offsetof ( typeof ( text ), u.settings ) +
-				string_copy ( text.u.settings,
-					      ui->row.value,
-					      sizeof ( text.u.settings ) ) );
+		value = ( ( ui->row.settings == ui->settings->parent ) ?
+			  ".." : ui->row.settings->name );
+		curs_offset = string_copy ( text.u.settings.name, value,
+					    sizeof ( text.u.settings.name ) );
+		text.u.settings.name[curs_offset] = '/';
+		curs_offset += offsetof ( typeof ( text ), u.settings );
 
 	} else {
 
@@ -221,12 +224,12 @@ static void draw_setting_row ( struct settings_ui *ui ) {
 			      sizeof ( text.u.setting.name ) );
 
 		/* Construct space-padded value */
-		value = ui->row.value;
-		if ( ! *value )
+		value = ui->row.buf;
+		if ( ! ( value && value[0] ) )
 			value = "<not specified>";
-		curs_offset = ( offsetof ( typeof ( text ), u.setting.value ) +
-				string_copy ( text.u.setting.value, value,
-					      sizeof ( text.u.setting.value )));
+		curs_offset = string_copy ( text.u.setting.value, value,
+					    sizeof ( text.u.setting.value ) );
+		curs_offset += offsetof ( typeof ( text ), u.setting.value );
 	}
 
 	/* Print row */
@@ -257,7 +260,7 @@ static int edit_setting ( struct settings_ui *ui, int key ) {
  */
 static int save_setting ( struct settings_ui *ui ) {
 	assert ( ui->row.setting.name != NULL );
-	return storef_setting ( ui->settings, &ui->row.setting, ui->row.value );
+	return storef_setting ( ui->settings, &ui->row.setting, ui->row.buf );
 }
 
 /**
@@ -527,6 +530,7 @@ static int main_loop ( struct settings *settings ) {
 			redraw = 1;
 			break;
 		case CTRL_X:
+			select_setting_row ( &ui, -1U );
 			return 0;
 		case CR:
 		case LF:
diff --git a/src/include/ipxe/editbox.h b/src/include/ipxe/editbox.h
index 2c70e0b..c14bbdc 100644
--- a/src/include/ipxe/editbox.h
+++ b/src/include/ipxe/editbox.h
@@ -36,7 +36,7 @@ enum edit_box_flags {
 	EDITBOX_STARS = 0x0001,
 };
 
-extern void init_editbox ( struct edit_box *box, char *buf, size_t len,
+extern void init_editbox ( struct edit_box *box, char **buf,
 			   WINDOW *win, unsigned int row, unsigned int col,
 			   unsigned int width, unsigned int flags )
 			   __attribute__ (( nonnull (1, 2) ));
diff --git a/src/include/ipxe/editstring.h b/src/include/ipxe/editstring.h
index a00a8ad..7ad8fb3 100644
--- a/src/include/ipxe/editstring.h
+++ b/src/include/ipxe/editstring.h
@@ -11,10 +11,8 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
 
 /** An editable string */
 struct edit_string {
-	/** Buffer for string */
-	char *buf;
-	/** Size of buffer (including terminating NUL) */
-	size_t len;
+	/** Dynamically allocated string buffer */
+	char **buf;
 	/** Cursor position */
 	unsigned int cursor;
 
@@ -32,17 +30,28 @@ struct edit_string {
  * Initialise editable string
  *
  * @v string		Editable string
- * @v buf		Buffer for string
- * @v len		Length of buffer
+ * @v buf		Dynamically allocated string buffer
+ *
+ * The @c buf parameter must be the address of a caller-provided
+ * pointer to a NUL-terminated string allocated using malloc() (or
+ * equivalent, such as strdup()).  Any edits made to the string will
+ * realloc() the string buffer as needed.
+ *
+ * The caller may choose leave the initial string buffer pointer as @c
+ * NULL, in which case it will be allocated upon the first attempt to
+ * insert a character into the buffer.  If the caller does this, then
+ * it must be prepared to find the pointer still @c NULL after
+ * editing, since the user may never attempt to insert any characters.
  */
-static inline void init_editstring ( struct edit_string *string, char *buf,
-				     size_t len ) {
+static inline __nonnull void init_editstring ( struct edit_string *string,
+					       char **buf ) {
+
 	string->buf = buf;
-	string->len = len;
 }
 
-extern void replace_string ( struct edit_string *string,
-			     const char *replacement ) __nonnull;
-extern int edit_string ( struct edit_string *string, int key ) __nonnull;
+extern __attribute__ (( nonnull ( 1 ) )) int
+replace_string ( struct edit_string *string, const char *replacement );
+
+extern __nonnull int edit_string ( struct edit_string *string, int key );
 
 #endif /* _IPXE_EDITSTRING_H */
diff --git a/src/include/ipxe/errfile.h b/src/include/ipxe/errfile.h
index 0ab3723..96981dd 100644
--- a/src/include/ipxe/errfile.h
+++ b/src/include/ipxe/errfile.h
@@ -416,6 +416,7 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
 #define ERRFILE_efi_settings	      ( ERRFILE_OTHER | 0x005e0000 )
 #define ERRFILE_x25519		      ( ERRFILE_OTHER | 0x005f0000 )
 #define ERRFILE_des		      ( ERRFILE_OTHER | 0x00600000 )
+#define ERRFILE_editstring	      ( ERRFILE_OTHER | 0x00610000 )
 
 /** @} */