arch/i386/boot/cmdline.c

   1 /* -*- linux-c -*- ------------------------------------------------------- *
   2  *
   3  *   Copyright (C) 1991, 1992 Linus Torvalds
   4  *   Copyright 2007 rPath, Inc. - All Rights Reserved
   5  *
   6  *   This file is part of the Linux kernel, and is made available under
   7  *   the terms of the GNU General Public License version 2.
   8  *
   9  * ----------------------------------------------------------------------- */
  10
  11 /*
  12  * arch/i386/boot/cmdline.c
  13  *
  14  * Simple command-line parser for early boot.
  15  */
  16
  17 #include "boot.h"
  18
  19 static inline int myisspace(u8 c)
  20 {
  21         return c <= ' ';        /* Close enough approximation */
  22 }
  23
  24 /*
  25  * Find a non-boolean option, that is, "option=argument".  In accordance
  26  * with standard Linux practice, if this option is repeated, this returns
  27  * the last instance on the command line.
  28  *
  29  * Returns the length of the argument (regardless of if it was
  30  * truncated to fit in the buffer), or -1 on not found.
  31  */
  32 int cmdline_find_option(const char *option, char *buffer, int bufsize)
  33 {
  34         u32 cmdline_ptr = boot_params.hdr.cmd_line_ptr;
  35         addr_t cptr;
  36         char c;
  37         int len = -1;
  38         const char *opptr = NULL;
  39         char *bufptr = buffer;
  40         enum {
  41                 st_wordstart,   /* Start of word/after whitespace */
  42                 st_wordcmp,     /* Comparing this word */
  43                 st_wordskip,    /* Miscompare, skip */
  44                 st_bufcpy       /* Copying this to buffer */
  45         } state = st_wordstart;
  46
  47         if (!cmdline_ptr || cmdline_ptr >= 0x100000)
  48                 return -1;      /* No command line, or inaccessible */
  49
  50         cptr = cmdline_ptr & 0xf;
  51         set_fs(cmdline_ptr >> 4);
  52
  53         while (cptr < 0x10000 && (c = rdfs8(cptr++))) {
  54                 switch (state) {
  55                 case st_wordstart:
  56                         if (myisspace(c))
  57                                 break;
  58
  59                         /* else */
  60                         state = st_wordcmp;
  61                         opptr = option;
  62                         /* fall through */
  63
  64                 case st_wordcmp:
  65                         if (c == '=' && !*opptr) {
  66                                 len = 0;
  67                                 bufptr = buffer;
  68                                 state = st_bufcpy;
  69                         } else if (myisspace(c)) {
  70                                 state = st_wordstart;
  71                         } else if (c != *opptr++) {
  72                                 state = st_wordskip;
  73                         }
  74                         break;
  75
  76                 case st_wordskip:
  77                         if (myisspace(c))
  78                                 state = st_wordstart;
  79                         break;
  80
  81                 case st_bufcpy:
  82                         if (myisspace(c)) {
  83                                 state = st_wordstart;
  84                         } else {
  85                                 if (len < bufsize-1)
  86                                         *bufptr++ = c;
  87                                 len++;
  88                         }
  89                         break;
  90                 }
  91         }
  92
  93         if (bufsize)
  94                 *bufptr = '\0';
  95
  96         return len;
  97 }