poll: rust: allow poll_table ptrs to be null

It's possible for a poll_table to be null. This can happen if an
end-user just wants to know if a resource has events right now without
registering a waiter for when events become available. Furthermore,
these null pointers should be handled transparently by the API, so we
should not change `from_ptr` to return an `Option`. Thus, change
`PollTable` to wrap a raw pointer rather than use a reference so that
you can pass null.

Comments mentioning `struct poll_table` are changed to just `poll_table`
since `poll_table` is a typedef. (It's a typedef because it's supposed
to be opaque.)

Reviewed-by: Benno Lossin <lossin@kernel.org>
Signed-off-by: Alice Ryhl <aliceryhl@google.com>

1 files changed, 10 insertions, 0 deletions

diff --git a/rust/helpers/poll.c b/rust/helpers/poll.c
new file mode 100644
index 000000000000..7e5b1751c2d5
--- /dev/null
+++ b/rust/helpers/poll.c
@@ -0,0 +1,10 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/export.h>
+#include <linux/poll.h>
+
+void rust_helper_poll_wait(struct file *filp, wait_queue_head_t *wait_address,
+			   poll_table *p)
+{
+	poll_wait(filp, wait_address, p);
+}