Revert "Revert "fs: don't allow splice read/write without explicit ops""

This reverts commit 6a0e0ecdd4b27a73d289a5ca24e580d804a2cb5a.

Bug: 171770067
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
Change-Id: I796a9872e32f750c9058d04f0faf408c541fac94
diff --git a/fs/read_write.c b/fs/read_write.c
index 551b1d2..25fb21b 100644
--- a/fs/read_write.c
+++ b/fs/read_write.c
@@ -1085,7 +1085,7 @@ ssize_t vfs_iter_write(struct file *file, struct iov_iter *iter, loff_t *ppos,
 }
 EXPORT_SYMBOL(vfs_iter_write);
 
-ssize_t vfs_readv(struct file *file, const struct iovec __user *vec,
+static ssize_t vfs_readv(struct file *file, const struct iovec __user *vec,
 		  unsigned long vlen, loff_t *pos, rwf_t flags)
 {
 	struct iovec iovstack[UIO_FASTIOV];