io_uring/fs: consider link->flags when getting path for LINKAT

In order for `AT_EMPTY_PATH` to work as expected, the fact
that the user wants that behavior needs to make it to `getname_flags`
or it will return ENOENT.

Fixes: cf30da9 ("io_uring: add support for IORING_OP_LINKAT")
Cc:  <[email protected]>
Link: axboe/liburing#995
Signed-off-by: Charles Mirabile <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jens Axboe <[email protected]>

Author: Charles Mirabile

io_uring/fs.c

@@ -254,7 +254,7 @@ int io_linkat_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 	newf = u64_to_user_ptr(READ_ONCE(sqe->addr2));
 	lnk->flags = READ_ONCE(sqe->hardlink_flags);
 
-	lnk->oldpath = getname(oldf);
+	lnk->oldpath = getname_uflags(oldf, lnk->flags);
 	if (IS_ERR(lnk->oldpath))
 		return PTR_ERR(lnk->oldpath);