lib: add lib/glob.c

This is a helper function from drivers/ata/libata_core.c, where it is
used to blacklist particular device models.  It's being moved to lib/ so
other drivers may use it for the same purpose.

This implementation in non-recursive, so is safe for the kernel stack.

[akpm@linux-foundation.org: fix sparse warning]
Signed-off-by: George Spelvin <linux@horizon.com>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Tejun Heo <tj@kernel.org>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 123 insertions, 0 deletions

diff --git a/lib/glob.c b/lib/glob.c
new file mode 100644
index 000000000000..0ba3ea86b546
--- /dev/null
+++ b/lib/glob.c
@@ -0,0 +1,123 @@
+#include <linux/module.h>
+#include <linux/glob.h>
+
+/*
+ * The only reason this code can be compiled as a module is because the
+ * ATA code that depends on it can be as well.  In practice, they're
+ * both usually compiled in and the module overhead goes away.
+ */
+MODULE_DESCRIPTION("glob(7) matching");
+MODULE_LICENSE("Dual MIT/GPL");
+
+/**
+ * glob_match - Shell-style pattern matching, like !fnmatch(pat, str, 0)
+ * @pat: Shell-style pattern to match, e.g. "*.[ch]".
+ * @str: String to match.  The pattern must match the entire string.
+ *
+ * Perform shell-style glob matching, returning true (1) if the match
+ * succeeds, or false (0) if it fails.  Equivalent to !fnmatch(@pat, @str, 0).
+ *
+ * Pattern metacharacters are ?, *, [ and \.
+ * (And, inside character classes, !, - and ].)
+ *
+ * This is small and simple implementation intended for device blacklists
+ * where a string is matched against a number of patterns.  Thus, it
+ * does not preprocess the patterns.  It is non-recursive, and run-time
+ * is at most quadratic: strlen(@str)*strlen(@pat).
+ *
+ * An example of the worst case is glob_match("*aaaaa", "aaaaaaaaaa");
+ * it takes 6 passes over the pattern before matching the string.
+ *
+ * Like !fnmatch(@pat, @str, 0) and unlike the shell, this does NOT
+ * treat / or leading . specially; it isn't actually used for pathnames.
+ *
+ * Note that according to glob(7) (and unlike bash), character classes
+ * are complemented by a leading !; this does not support the regex-style
+ * [^a-z] syntax.
+ *
+ * An opening bracket without a matching close is matched literally.
+ */
+bool __pure glob_match(char const *pat, char const *str)
+{
+        /*
+         * Backtrack to previous * on mismatch and retry starting one
+         * character later in the string.  Because * matches all characters
+         * (no exception for /), it can be easily proved that there's
+         * never a need to backtrack multiple levels.
+         */
+        char const *back_pat = NULL, *back_str = back_str;
+
+        /*
+         * Loop over each token (character or class) in pat, matching
+         * it against the remaining unmatched tail of str.  Return false
+         * on mismatch, or true after matching the trailing nul bytes.
+         */
+        for (;;) {
+                unsigned char c = *str++;
+                unsigned char d = *pat++;
+
+                switch (d) {
+                case '?':       /* Wildcard: anything but nul */
+                        if (c == '\0')
+                                return false;
+                        break;
+                case '*':       /* Any-length wildcard */
+                        if (*pat == '\0')       /* Optimize trailing * case */
+                                return true;
+                        back_pat = pat;
+                        back_str = --str;       /* Allow zero-length match */
+                        break;
+                case '[': {     /* Character class */
+                        bool match = false, inverted = (*pat == '!');
+                        char const *class = pat + inverted;
+                        unsigned char a = *class++;
+
+                        /*
+                         * Iterate over each span in the character class.
+                         * A span is either a single character a, or a
+                         * range a-b.  The first span may begin with ']'.
+                         */
+                        do {
+                                unsigned char b = a;
+
+                                if (a == '\0')  /* Malformed */
+                                        goto literal;
+
+                                if (class[0] == '-' && class[1] != ']') {
+                                        b = class[1];
+
+                                        if (b == '\0')
+                                                goto literal;
+
+                                        class += 2;
+                                        /* Any special action if a > b? */
+                                }
+                                match |= (a <= c && c <= b);
+                        } while ((a = *class++) != ']');
+
+                        if (match == inverted)
+                                goto backtrack;
+                        pat = class;
+                        }
+                        break;
+                case '\\':
+                        d = *pat++;
+                        /*FALLTHROUGH*/
+                default:        /* Literal character */
+literal:
+                        if (c == d) {
+                                if (d == '\0')
+                                        return true;
+                                break;
+                        }
+backtrack:
+                        if (c == '\0' || !back_pat)
+                                return false;   /* No point continuing */
+                        /* Try again from last *, one character later in str. */
+                        pat = back_pat;
+                        str = ++back_str;
+                        break;
+                }
+        }
+}
+EXPORT_SYMBOL(glob_match);