arch/x86/lib/cmdline.c

   1 /*
   2  * This file is part of the Linux kernel, and is made available under
   3  * the terms of the GNU General Public License version 2.
   4  *
   5  * Misc librarized functions for cmdline poking.
   6  */
   7 #include <linux/kernel.h>
   8 #include <linux/string.h>
   9 #include <linux/ctype.h>
  10 #include <asm/setup.h>
  11
  12 static inline int myisspace(u8 c)
  13 {
  14         return c <= ' ';        /* Close enough approximation */
  15 }
  16
  17 /**
  18  * Find a boolean option (like quiet,noapic,nosmp....)
  19  *
  20  * @cmdline: the cmdline string
  21  * @option: option string to look for
  22  *
  23  * Returns the position of that @option (starts counting with 1)
  24  * or 0 on not found.  @option will only be found if it is found
  25  * as an entire word in @cmdline.  For instance, if @option="car"
  26  * then a cmdline which contains "cart" will not match.
  27  */
  28 static int
  29 __cmdline_find_option_bool(const char *cmdline, int max_cmdline_size,
  30                            const char *option)
  31 {
  32         char c;
  33         int pos = 0, wstart = 0;
  34         const char *opptr = NULL;
  35         enum {
  36                 st_wordstart = 0,       /* Start of word/after whitespace */
  37                 st_wordcmp,     /* Comparing this word */
  38                 st_wordskip,    /* Miscompare, skip */
  39         } state = st_wordstart;
  40
  41         if (!cmdline)
  42                 return -1;      /* No command line */
  43
  44         /*
  45          * This 'pos' check ensures we do not overrun
  46          * a non-NULL-terminated 'cmdline'
  47          */
  48         while (pos < max_cmdline_size) {
  49                 c = *(char *)cmdline++;
  50                 pos++;
  51
  52                 switch (state) {
  53                 case st_wordstart:
  54                         if (!c)
  55                                 return 0;
  56                         else if (myisspace(c))
  57                                 break;
  58
  59                         state = st_wordcmp;
  60                         opptr = option;
  61                         wstart = pos;
  62                         /* fall through */
  63
  64                 case st_wordcmp:
  65                         if (!*opptr) {
  66                                 /*
  67                                  * We matched all the way to the end of the
  68                                  * option we were looking for.  If the
  69                                  * command-line has a space _or_ ends, then
  70                                  * we matched!
  71                                  */
  72                                 if (!c || myisspace(c))
  73                                         return wstart;
  74                                 /*
  75                                  * We hit the end of the option, but _not_
  76                                  * the end of a word on the cmdline.  Not
  77                                  * a match.
  78                                  */
  79                         } else if (!c) {
  80                                 /*
  81                                  * Hit the NULL terminator on the end of
  82                                  * cmdline.
  83                                  */
  84                                 return 0;
  85                         } else if (c == *opptr++) {
  86                                 /*
  87                                  * We are currently matching, so continue
  88                                  * to the next character on the cmdline.
  89                                  */
  90                                 break;
  91                         }
  92                         state = st_wordskip;
  93                         /* fall through */
  94
  95                 case st_wordskip:
  96                         if (!c)
  97                                 return 0;
  98                         else if (myisspace(c))
  99                                 state = st_wordstart;
 100                         break;
 101                 }
 102         }
 103
 104         return 0;       /* Buffer overrun */
 105 }
 106
 107 int cmdline_find_option_bool(const char *cmdline, const char *option)
 108 {
 109         return __cmdline_find_option_bool(cmdline, COMMAND_LINE_SIZE, option);
 110 }