lib: hex2bin converts ascii hexadecimal string to binary

Similar to the kgdb_hex2mem() code, hex2bin converts a string
to binary using the hex_to_bin() library call.

Changelog:
- Replace parameter names with src/dst (based on David Howell's comment)
- Add 'const' where needed (based on David Howell's comment)
- Replace int with size_t (based on David Howell's comment)

Signed-off-by: Mimi Zohar <zohar@us.ibm.com>
Acked-by: Serge E. Hallyn <serge@hallyn.com>
Acked-by: David Howells <dhowells@redhat.com>
Signed-off-by: James Morris <jmorris@namei.org>

include/linux/kernel.h

@@ -265,6 +265,7 @@ static inline char *pack_hex_byte(char *buf, u8 byte)
 }
 
 extern int hex_to_bin(char ch);
+extern void hex2bin(u8 *dst, const char *src, size_t count);
 
 /*
  * General tracing related utility functions - trace_printk(),

lib/hexdump.c

@@ -33,6 +33,22 @@ int hex_to_bin(char ch)
 }
 EXPORT_SYMBOL(hex_to_bin);
 
+/**
+ * hex2bin - convert an ascii hexadecimal string to its binary representation
+ * @dst: binary result
+ * @src: ascii hexadecimal string
+ * @count: result length
+ */
+void hex2bin(u8 *dst, const char *src, size_t count)
+{
+	while (count--) {
+		*dst = hex_to_bin(*src++) << 4;
+		*dst += hex_to_bin(*src++);
+		dst++;
+	}
+}
+EXPORT_SYMBOL(hex2bin);
+
 /**
  * hex_dump_to_buffer - convert a blob of data to "hex ASCII" in memory
  * @buf: data blob to dump