lib/glob.c

   1 #include <linux/module.h>
   2 #include <linux/glob.h>
   3
   4 /*
   5  * The only reason this code can be compiled as a module is because the
   6  * ATA code that depends on it can be as well.  In practice, they're
   7  * both usually compiled in and the module overhead goes away.
   8  */
   9 MODULE_DESCRIPTION("glob(7) matching");
  10 MODULE_LICENSE("Dual MIT/GPL");
  11
  12 /**
  13  * glob_match - Shell-style pattern matching, like !fnmatch(pat, str, 0)
  14  * @pat: Shell-style pattern to match, e.g. "*.[ch]".
  15  * @str: String to match.  The pattern must match the entire string.
  16  *
  17  * Perform shell-style glob matching, returning true (1) if the match
  18  * succeeds, or false (0) if it fails.  Equivalent to !fnmatch(@pat, @str, 0).
  19  *
  20  * Pattern metacharacters are ?, *, [ and \.
  21  * (And, inside character classes, !, - and ].)
  22  *
  23  * This is small and simple implementation intended for device blacklists
  24  * where a string is matched against a number of patterns.  Thus, it
  25  * does not preprocess the patterns.  It is non-recursive, and run-time
  26  * is at most quadratic: strlen(@str)*strlen(@pat).
  27  *
  28  * An example of the worst case is glob_match("*aaaaa", "aaaaaaaaaa");
  29  * it takes 6 passes over the pattern before matching the string.
  30  *
  31  * Like !fnmatch(@pat, @str, 0) and unlike the shell, this does NOT
  32  * treat / or leading . specially; it isn't actually used for pathnames.
  33  *
  34  * Note that according to glob(7) (and unlike bash), character classes
  35  * are complemented by a leading !; this does not support the regex-style
  36  * [^a-z] syntax.
  37  *
  38  * An opening bracket without a matching close is matched literally.
  39  */
  40 bool __pure glob_match(char const *pat, char const *str)
  41 {
  42         /*
  43          * Backtrack to previous * on mismatch and retry starting one
  44          * character later in the string.  Because * matches all characters
  45          * (no exception for /), it can be easily proved that there's
  46          * never a need to backtrack multiple levels.
  47          */
  48         char const *back_pat = NULL, *back_str = back_str;
  49
  50         /*
  51          * Loop over each token (character or class) in pat, matching
  52          * it against the remaining unmatched tail of str.  Return false
  53          * on mismatch, or true after matching the trailing nul bytes.
  54          */
  55         for (;;) {
  56                 unsigned char c = *str++;
  57                 unsigned char d = *pat++;
  58
  59                 switch (d) {
  60                 case '?':       /* Wildcard: anything but nul */
  61                         if (c == '\0')
  62                                 return false;
  63                         break;
  64                 case '*':       /* Any-length wildcard */
  65                         if (*pat == '\0')       /* Optimize trailing * case */
  66                                 return true;
  67                         back_pat = pat;
  68                         back_str = --str;       /* Allow zero-length match */
  69                         break;
  70                 case '[': {     /* Character class */
  71                         bool match = false, inverted = (*pat == '!');
  72                         char const *class = pat + inverted;
  73                         unsigned char a = *class++;
  74
  75                         /*
  76                          * Iterate over each span in the character class.
  77                          * A span is either a single character a, or a
  78                          * range a-b.  The first span may begin with ']'.
  79                          */
  80                         do {
  81                                 unsigned char b = a;
  82
  83                                 if (a == '\0')  /* Malformed */
  84                                         goto literal;
  85
  86                                 if (class[0] == '-' && class[1] != ']') {
  87                                         b = class[1];
  88
  89                                         if (b == '\0')
  90                                                 goto literal;
  91
  92                                         class += 2;
  93                                         /* Any special action if a > b? */
  94                                 }
  95                                 match |= (a <= c && c <= b);
  96                         } while ((a = *class++) != ']');
  97
  98                         if (match == inverted)
  99                                 goto backtrack;
 100                         pat = class;
 101                         }
 102                         break;
 103                 case '\\':
 104                         d = *pat++;
 105                         fallthrough;
 106                 default:        /* Literal character */
 107 literal:
 108                         if (c == d) {
 109                                 if (d == '\0')
 110                                         return true;
 111                                 break;
 112                         }
 113 backtrack:
 114                         if (c == '\0' || !back_pat)
 115                                 return false;   /* No point continuing */
 116                         /* Try again from last *, one character later in str. */
 117                         pat = back_pat;
 118                         str = ++back_str;
 119                         break;
 120                 }
 121         }
 122 }
 123 EXPORT_SYMBOL(glob_match);