linux/arch/x86/boot/cmdline.c

/* -*- 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;
}