[settings] Add "read" command

The "read" command allows a script to prompt a user to enter a
setting.  For example:

  echo -n Static IP address:
  read net0/ip

Total cost: 17 bytes.

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

src/hci/commands/nvo_cmd.c

 #include <ipxe/settings.h>
 #include <ipxe/command.h>
 #include <ipxe/parseopt.h>
+#include <readline/readline.h>
 
 FILE_LICENCE ( GPL2_OR_LATER );
 
 	return 0;
 }
 
-/** "set" options */
-struct set_options {};
+/** "set", "clear", and "read" options */
+struct set_core_options {};
 
-/** "set" option list */
-static struct option_descriptor set_opts[] = {};
+/** "set", "clear", and "read" option list */
+static struct option_descriptor set_core_opts[] = {};
 
 /** "set" command descriptor */
 static struct command_descriptor set_cmd =
-	COMMAND_DESC ( struct set_options, set_opts, 1, MAX_ARGUMENTS,
+	COMMAND_DESC ( struct set_core_options, set_core_opts, 1, MAX_ARGUMENTS,
 		       "<setting> <value>" );
 
+/** "clear" and "read" command descriptor */
+static struct command_descriptor clear_read_cmd =
+	COMMAND_DESC ( struct set_core_options, set_core_opts, 1, 1,
+		       "<setting>" );
+
 /**
- * "set" command
+ * "set", "clear", and "read" command
  *
  * @v argc		Argument count
  * @v argv		Argument list
+ * @v cmd		Command descriptor
+ * @v get_value		Method to obtain setting value
  * @ret rc		Return status code
  */
-static int set_exec ( int argc, char **argv ) {
-	struct set_options opts;
+static int set_core_exec ( int argc, char **argv,
+			   struct command_descriptor *cmd,
+			   int ( * get_value ) ( char **args, char **value ) ) {
+	struct set_core_options opts;
 	const char *name;
 	char *value;
 	int rc;
 
 	/* Parse options */
-	if ( ( rc = parse_options ( argc, argv, &set_cmd, &opts ) ) != 0 )
+	if ( ( rc = parse_options ( argc, argv, cmd, &opts ) ) != 0 )
 		goto err_parse_options;
 
 	/* Parse setting name */
 	name = argv[optind];
 
 	/* Parse setting value */
-	value = concat_args ( &argv[ optind + 1 ] );
-	if ( ! value ) {
-		rc = -ENOMEM;
-		goto err_concat_args;
-	}
+	if ( ( rc = get_value ( &argv[ optind + 1 ], &value ) ) != 0 )
+		goto err_get_value;
 
 	/* Determine total length of command line */
 	if ( ( rc = storef_named_setting ( name, value ) ) != 0 ) {
-		printf ( "Could not set \"%s\"=\"%s\": %s\n",
-			 name, value, strerror ( rc ) );
+		printf ( "Could not %s \"%s\": %s\n",
+			 argv[0], name, strerror ( rc ) );
 		goto err_store;
 	}
 
 
  err_store:
 	free ( value );
- err_concat_args:
+ err_get_value:
  err_parse_options:
 	return rc;
 }
 
-/** "clear" options */
-struct clear_options {};
+/**
+ * Get setting value for "set" command
+ *
+ * @v args		Remaining arguments
+ * @ret value		Setting value
+ * @ret rc		Return status code
+ */
+static int set_value ( char **args, char **value ) {
+
+	*value = concat_args ( args );
+	if ( ! *value )
+		return -ENOMEM;
+
+	return 0;
+}
+
+/**
+ * "set" command
+ *
+ * @v argc		Argument count
+ * @v argv		Argument list
+ * @ret rc		Return status code
+ */
+static int set_exec ( int argc, char **argv ) {
+	return set_core_exec ( argc, argv, &set_cmd, set_value );
+}
 
-/** "clear" option list */
-static struct option_descriptor clear_opts[] = {};
+/**
+ * Get setting value for "clear" command
+ *
+ * @v args		Remaining arguments
+ * @ret value		Setting value
+ * @ret rc		Return status code
+ */
+static int clear_value ( char **args __unused, char **value ) {
 
-/** "clear" command descriptor */
-static struct command_descriptor clear_cmd =
-	COMMAND_DESC ( struct clear_options, clear_opts, 1, 1, "<setting>" );
+	*value = NULL;
+	return 0;
+}
 
 /**
  * "clear" command
  * @ret rc		Return status code
  */
 static int clear_exec ( int argc, char **argv ) {
-	struct clear_options opts;
-	const char *name;
-	int rc;
+	return set_core_exec ( argc, argv, &clear_read_cmd, clear_value );
+}
 
-	/* Parse options */
-	if ( ( rc = parse_options ( argc, argv, &clear_cmd, &opts ) ) != 0 )
-		return rc;
+/**
+ * Get setting value for "read" command
+ *
+ * @ret value		Setting value
+ * @ret rc		Return status code
+ */
+static int read_value ( char **args __unused, char **value ) {
 
-	/* Parse setting name */
-	name = argv[optind];
+	*value = readline ( NULL );
+	if ( ! *value )
+		return -ENOMEM;
 
-	/* Clear setting */
-	if ( ( rc = delete_named_setting ( name ) ) != 0 ) {
-		printf ( "Could not clear \"%s\": %s\n",
-			 name, strerror ( rc ) );
-		return rc;
-	}
-	
 	return 0;
 }
 
+/**
+ * "read" command
+ *
+ * @v argc		Argument count
+ * @v argv		Argument list
+ * @ret rc		Return status code
+ */
+static int read_exec ( int argc, char **argv ) {
+	return set_core_exec ( argc, argv, &clear_read_cmd, read_value );
+}
+
 /** Non-volatile option commands */
 struct command nvo_commands[] __command = {
 	{
 		.name = "clear",
 		.exec = clear_exec,
 	},
+	{
+		.name = "read",
+		.exec = read_exec,
+	},
 };