sock: Introduce cred_to_ucred

To keep the coming code clear and to allow both the sock
code and the scm code to share the logic introduce a
fuction to translate from struct cred to struct ucred.

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Acked-by: Pavel Emelyanov <xemul@openvz.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/linux/socket.h b/include/linux/socket.h
index 032a19e..a2fada9 100644
--- a/include/linux/socket.h
+++ b/include/linux/socket.h
@@ -24,6 +24,9 @@
 #include <linux/types.h>		/* pid_t			*/
 #include <linux/compiler.h>		/* __user			*/
 
+struct pid;
+struct cred;
+
 #define __sockaddr_check_size(size)	\
 	BUILD_BUG_ON(((size) > sizeof(struct __kernel_sockaddr_storage)))
 
@@ -309,6 +312,8 @@
 #define IPX_TYPE	1
 
 #ifdef __KERNEL__
+extern void cred_to_ucred(struct pid *pid, const struct cred *cred, struct ucred *ucred);
+
 extern int memcpy_fromiovec(unsigned char *kdata, struct iovec *iov, int len);
 extern int memcpy_fromiovecend(unsigned char *kdata, const struct iovec *iov,
 			       int offset, int len);