io_uring: refactor compat_msghdr import

Add an entry for user pointer to compat_msghdr into io_connect, so it's
explicit that we may use it as this, and removes annoying casts.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/73fd644dea1518f528d3648981cf777ce6e537e9.1618101759.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

fs/io_uring.c

@@ -570,8 +570,9 @@ struct io_connect {
 struct io_sr_msg {
 	struct file			*file;
 	union {
-		struct user_msghdr __user *umsg;
+		struct compat_msghdr __user	*umsg_compat;
-		void __user		*buf;
+		struct user_msghdr __user	*umsg;
+		void __user			*buf;
 	};
 	int				msg_flags;
 	int				bgid;
@@ -4435,16 +4436,14 @@ static int __io_recvmsg_copy_hdr(struct io_kiocb *req,
 static int __io_compat_recvmsg_copy_hdr(struct io_kiocb *req,
 					struct io_async_msghdr *iomsg)
 {
-	struct compat_msghdr __user *msg_compat;
 	struct io_sr_msg *sr = &req->sr_msg;
 	struct compat_iovec __user *uiov;
 	compat_uptr_t ptr;
 	compat_size_t len;
 	int ret;
 
-	msg_compat = (struct compat_msghdr __user *) sr->umsg;
+	ret = __get_compat_msghdr(&iomsg->msg, sr->umsg_compat, &iomsg->uaddr,
-	ret = __get_compat_msghdr(&iomsg->msg, msg_compat, &iomsg->uaddr,
+				  &ptr, &len);
-					&ptr, &len);
 	if (ret)
 		return ret;