[script] Implement "goto" in iPXE scripts

Allow script labels to be defined using the syntax

  :<labelname>

(nothing else allowed on the line, including whitespace).  Labels are
ignored during script execution, but can be used as the target of the
"goto" command.  For example:

  #!ipxe

  goto machine_${net0/ip} || goto machine_default

  # Linux kernel boot
  :machine_10.0.0.101
  :machine_10.0.0.102
  set filename http://my.boot.server/vmlinuz
  goto done

  # Default configuration
  :machine_default
  set filename pxelinux.0
  goto done

  # Boot selected configuration
  :done
  chain ${filename}

Originally-implemented-by: Shao Miller <shao.miller@yrdsb.edu.on.ca>
Originally-implemented-by: Stefan Hajnoczi <stefanha@gmail.com>
Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/image/script.c

@@ -27,12 +27,119 @@ FILE_LICENCE ( GPL2_OR_LATER );
 
 #include <string.h>
 #include <stdlib.h>
+#include <stdio.h>
 #include <ctype.h>
 #include <errno.h>
+#include <getopt.h>
+#include <ipxe/command.h>
+#include <ipxe/parseopt.h>
 #include <ipxe/image.h>
 
 struct image_type script_image_type __image_type ( PROBE_NORMAL );
 
+/** Currently running script
+ *
+ * This is a global in order to allow goto_exec() to update the
+ * offset.
+ */
+static struct image *script;
+
+/** Offset within current script
+ *
+ * This is a global in order to allow goto_exec() to update the
+ * offset.
+ */
+static size_t script_offset;
+
+/**
+ * Process script lines
+ *
+ * @v process_line	Line processor
+ * @v terminate		Termination check
+ * @ret rc		Return status code
+ */
+static int process_script ( int ( * process_line ) ( const char *line ),
+			    int ( * terminate ) ( int rc ) ) {
+	off_t eol;
+	size_t len;
+	int rc;
+
+	script_offset = 0;
+
+	do {
+	
+		/* Find length of next line, excluding any terminating '\n' */
+		eol = memchr_user ( script->data, script_offset, '\n',
+				    ( script->len - script_offset ) );
+		if ( eol < 0 )
+			eol = script->len;
+		len = ( eol - script_offset );
+
+		/* Copy line, terminate with NUL, and execute command */
+		{
+			char cmdbuf[ len + 1 ];
+
+			copy_from_user ( cmdbuf, script->data,
+					 script_offset, len );
+			cmdbuf[len] = '\0';
+			DBG ( "$ %s\n", cmdbuf );
+
+			/* Move to next line */
+			script_offset += ( len + 1 );
+
+			/* Process line */
+			rc = process_line ( cmdbuf );
+			if ( terminate ( rc ) )
+				return rc;
+		}
+
+	} while ( script_offset < script->len );
+
+	return rc;
+}
+
+/**
+ * Terminate script processing if line processing failed
+ *
+ * @v rc		Line processing status
+ * @ret terminate	Terminate script processing
+ */
+static int terminate_on_failure ( int rc ) {
+	return ( rc != 0 );
+}
+
+/**
+ * Terminate script processing if line processing succeeded
+ *
+ * @v rc		Line processing status
+ * @ret terminate	Terminate script processing
+ */
+static int terminate_on_success ( int rc ) {
+	return ( rc == 0 );
+}
+
+/**
+ * Execute script line
+ *
+ * @v line		Line of script
+ * @ret rc		Return status code
+ */
+static int script_exec_line ( const char *line ) {
+	int rc;
+
+	/* Skip label lines */
+	if ( line[0] == ':' )
+		return 0;
+
+	/* Execute command */
+	if ( ( rc = system ( line ) ) != 0 ) {
+		printf ( "Aborting on \"%s\"\n", line );
+		return rc;
+	}
+
+	return 0;
+}
+
 /**
  * Execute script
  *
@@ -40,9 +147,8 @@ struct image_type script_image_type __image_type ( PROBE_NORMAL );
  * @ret rc		Return status code
  */
 static int script_exec ( struct image *image ) {
-	size_t offset = 0;
-	off_t eol;
-	size_t len;
+	struct image *saved_script;
+	size_t saved_offset;
 	int rc;
 
 	/* Temporarily de-register image, so that a "boot" command
@@ -50,36 +156,19 @@ static int script_exec ( struct image *image ) {
 	 */
 	unregister_image ( image );
 
-	while ( offset < image->len ) {
-	
-		/* Find length of next line, excluding any terminating '\n' */
-		eol = memchr_user ( image->data, offset, '\n',
-				    ( image->len - offset ) );
-		if ( eol < 0 )
-			eol = image->len;
-		len = ( eol - offset );
+	/* Preserve state of any currently-running script */
+	saved_script = script;
+	saved_offset = script_offset;
 
-		/* Copy line, terminate with NUL, and execute command */
-		{
-			char cmdbuf[ len + 1 ];
+	/* Initialise state for this script */
+	script = image;
 
-			copy_from_user ( cmdbuf, image->data, offset, len );
-			cmdbuf[len] = '\0';
-			DBG ( "$ %s\n", cmdbuf );
-			if ( ( rc = system ( cmdbuf ) ) != 0 ) {
-				DBG ( "Command \"%s\" failed: %s\n",
-				      cmdbuf, strerror ( rc ) );
-				goto done;
-			}
-		}
-		
-		/* Move to next line */
-		offset += ( len + 1 );
-	}
+	/* Process script */
+	rc = process_script ( script_exec_line, terminate_on_failure );
 
-	rc = 0;
- done:
-	/* Re-register image and return */
+	/* Restore saved state, re-register image, and return */
+	script_offset = saved_offset;
+	script = saved_script;
 	register_image ( image );
 	return rc;
 }
@@ -129,3 +218,78 @@ struct image_type script_image_type __image_type ( PROBE_NORMAL ) = {
 	.load = script_load,
 	.exec = script_exec,
 };
+
+/** "goto" options */
+struct goto_options {};
+
+/** "goto" option list */
+static struct option_descriptor goto_opts[] = {};
+
+/** "goto" command descriptor */
+static struct command_descriptor goto_cmd =
+	COMMAND_DESC ( struct goto_options, goto_opts, 1, 1,
+		       "<label>", "" );
+
+/**
+ * Current "goto" label
+ *
+ * Valid only during goto_exec().  Consider this part of a closure.
+ */
+static const char *goto_label;
+
+/**
+ * Check for presence of label
+ *
+ * @v line		Script line
+ * @ret rc		Return status code
+ */
+static int goto_find_label ( const char *line ) {
+
+	if ( line[0] != ':' )
+		return -ENOENT;
+	if ( strcmp ( goto_label, &line[1] ) != 0 )
+		return -ENOENT;
+	return 0;
+}
+
+/**
+ * "goto" command
+ *
+ * @v argc		Argument count
+ * @v argv		Argument list
+ * @ret rc		Return status code
+ */
+static int goto_exec ( int argc, char **argv ) {
+	struct goto_options opts;
+	size_t saved_offset;
+	int rc;
+
+	/* Parse options */
+	if ( ( rc = parse_options ( argc, argv, &goto_cmd, &opts ) ) != 0 )
+		return rc;
+
+	/* Sanity check */
+	if ( ! script ) {
+		printf ( "Not in a script\n" );
+		return -ENOTTY;
+	}
+
+	/* Parse label */
+	goto_label = argv[optind];
+
+	/* Find label */
+	saved_offset = script_offset;
+	if ( ( rc = process_script ( goto_find_label,
+				     terminate_on_success ) ) != 0 ) {
+		script_offset = saved_offset;
+		return rc;
+	}
+
+	return 0;
+}
+
+/** "goto" command */
+struct command goto_command __command = {
+	.name = "goto",
+	.exec = goto_exec,
+};