Command-line parsing code for the new x86 setup code

/* -*- linux-c -*- ------------------------------------------------------- *

 *

 *   Copyright (C) 1991, 1992 Linus Torvalds

 *   Copyright 2007 rPath, Inc. - All Rights Reserved

 *

 *   This file is part of the Linux kernel, and is made available under

 *   the terms of the GNU General Public License version 2.

 *

 * ----------------------------------------------------------------------- */

/*

 * arch/i386/boot/cmdline.c

 *

 * Simple command-line parser for early boot.

 */

#include "boot.h"

static inline int myisspace(u8 c)

{

	return c <= ' ';	/* Close enough approximation */

}

/*

 * Find a non-boolean option, that is, "option=argument".  In accordance

 * with standard Linux practice, if this option is repeated, this returns

 * the last instance on the command line.

 *

 * Returns the length of the argument (regardless of if it was

 * truncated to fit in the buffer), or -1 on not found.

 */

int cmdline_find_option(const char *option, char *buffer, int bufsize)

{

	u32 cmdline_ptr = boot_params.hdr.cmd_line_ptr;

	addr_t cptr;

	char c;

	int len = -1;

	const char *opptr = NULL;

	char *bufptr = buffer;

	enum {

		st_wordstart,	/* Start of word/after whitespace */

		st_wordcmp,	/* Comparing this word */

		st_wordskip,	/* Miscompare, skip */

		st_bufcpy	/* Copying this to buffer */

	} state = st_wordstart;

	if (!cmdline_ptr || cmdline_ptr >= 0x100000)

		return -1;	/* No command line, or inaccessible */

	cptr = cmdline_ptr & 0xf;

	set_fs(cmdline_ptr >> 4);

	while (cptr < 0x10000 && (c = rdfs8(cptr++))) {

		switch (state) {

		case st_wordstart:

			if (myisspace(c))

				break;

			/* else */

			state = st_wordcmp;

			opptr = option;

			/* fall through */

		case st_wordcmp:

			if (c == '=' && !*opptr) {

				len = 0;

				bufptr = buffer;

				state = st_bufcpy;

			} else if (myisspace(c)) {

				state = st_wordstart;

			} else if (c != *opptr++) {

				state = st_wordskip;

			}

			break;

		case st_wordskip:

			if (myisspace(c))

				state = st_wordstart;

			break;

		case st_bufcpy:

			if (myisspace(c)) {

				state = st_wordstart;

			} else {

				if (len < bufsize-1)

					*bufptr++ = c;

				len++;

			}

			break;

		}

	}

	if (bufsize)

		*bufptr = '\0';

	return len;

}