lib/string_helpers: introduce generic string_unescape

There are several places in kernel where modules unescapes input to convert
C-Style Escape Sequences into byte codes.

The patch provides generic implementation of such approach. Test cases are
also included into the patch.

[akpm@linux-foundation.org: clarify comment]
[akpm@linux-foundation.org: export get_random_int() to modules]
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Samuel Thibault <samuel.thibault@ens-lyon.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jason Baron <jbaron@redhat.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: William Hubbs <w.d.hubbs@gmail.com>
Cc: Chris Brannon <chris@the-brannons.com>
Cc: Kirk Reiser <kirk@braille.uwo.ca>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 58 insertions, 0 deletions

diff --git a/include/linux/string_helpers.h b/include/linux/string_helpers.h
index a3eb2f65b656..3eeee9672a4a 100644
--- a/include/linux/string_helpers.h
+++ b/include/linux/string_helpers.h
@@ -13,4 +13,62 @@ enum string_size_units {
 int string_get_size(u64 size, enum string_size_units units,
                     char *buf, int len);
 
+#define UNESCAPE_SPACE          0x01
+#define UNESCAPE_OCTAL          0x02
+#define UNESCAPE_HEX            0x04
+#define UNESCAPE_SPECIAL        0x08
+#define UNESCAPE_ANY            \
+        (UNESCAPE_SPACE | UNESCAPE_OCTAL | UNESCAPE_HEX | UNESCAPE_SPECIAL)
+
+/**
+ * string_unescape - unquote characters in the given string
+ * @src:        source buffer (escaped)
+ * @dst:        destination buffer (unescaped)
+ * @size:       size of the destination buffer (0 to unlimit)
+ * @flags:      combination of the flags (bitwise OR):
+ *      %UNESCAPE_SPACE:
+ *              '\f' - form feed
+ *              '\n' - new line
+ *              '\r' - carriage return
+ *              '\t' - horizontal tab
+ *              '\v' - vertical tab
+ *      %UNESCAPE_OCTAL:
+ *              '\NNN' - byte with octal value NNN (1 to 3 digits)
+ *      %UNESCAPE_HEX:
+ *              '\xHH' - byte with hexadecimal value HH (1 to 2 digits)
+ *      %UNESCAPE_SPECIAL:
+ *              '\"' - double quote
+ *              '\\' - backslash
+ *              '\a' - alert (BEL)
+ *              '\e' - escape
+ *      %UNESCAPE_ANY:
+ *              all previous together
+ *
+ * Returns amount of characters processed to the destination buffer excluding
+ * trailing '\0'.
+ *
+ * Because the size of the output will be the same as or less than the size of
+ * the input, the transformation may be performed in place.
+ *
+ * Caller must provide valid source and destination pointers. Be aware that
+ * destination buffer will always be NULL-terminated. Source string must be
+ * NULL-terminated as well.
+ */
+int string_unescape(char *src, char *dst, size_t size, unsigned int flags);
+
+static inline int string_unescape_inplace(char *buf, unsigned int flags)
+{
+        return string_unescape(buf, buf, 0, flags);
+}
+
+static inline int string_unescape_any(char *src, char *dst, size_t size)
+{
+        return string_unescape(src, dst, size, UNESCAPE_ANY);
+}
+
+static inline int string_unescape_any_inplace(char *buf)
+{
+        return string_unescape_any(buf, buf, 0);
+}
+
 #endif