fuse_ioctl_copy_user(): don't open-code copy_page_{to,from}_iter()

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

fs/fuse/file.c

@@ -2339,31 +2339,15 @@ static int fuse_ioctl_copy_user(struct page **pages, struct iovec *iov,
 
 	while (iov_iter_count(&ii)) {
 		struct page *page = pages[page_idx++];
-		size_t todo = min_t(size_t, PAGE_SIZE, iov_iter_count(&ii));
-		void *kaddr;
+		size_t copied;
 
-		kaddr = kmap(page);
+		if (!to_user)
+			copied = copy_page_from_iter(page, 0, PAGE_SIZE, &ii);
+		else
+			copied = copy_page_to_iter(page, 0, PAGE_SIZE, &ii);
 
-		while (todo) {
-			char __user *uaddr = ii.iov->iov_base + ii.iov_offset;
-			size_t iov_len = ii.iov->iov_len - ii.iov_offset;
-			size_t copy = min(todo, iov_len);
-			size_t left;
-
-			if (!to_user)
-				left = copy_from_user(kaddr, uaddr, copy);
-			else
-				left = copy_to_user(uaddr, kaddr, copy);
-
-			if (unlikely(left))
-				return -EFAULT;
-
-			iov_iter_advance(&ii, copy);
-			todo -= copy;
-			kaddr += copy;
-		}
-
-		kunmap(page);
+		if (unlikely(copied != PAGE_SIZE && iov_iter_count(&ii)))
+			return -EFAULT;
 	}
 
 	return 0;