Messages in this thread | | | Date | Tue, 12 Dec 2023 17:01:28 +0000 | From | Benno Lossin <> | Subject | Re: [PATCH v2 7/7] rust: file: add abstraction for `poll_table` |
| |
On 12/12/23 10:59, Alice Ryhl wrote: > On Fri, Dec 8, 2023 at 6:53 PM Benno Lossin <benno.lossin@proton.me> wrote: >> On 12/6/23 12:59, Alice Ryhl wrote: >>> + fn get_qproc(&self) -> bindings::poll_queue_proc { >>> + let ptr = self.0.get(); >>> + // SAFETY: The `ptr` is valid because it originates from a reference, and the `_qproc` >>> + // field is not modified concurrently with this call since we have an immutable reference. >> >> This needs an invariant on `PollTable` (i.e. `self.0` is valid). > > How would you phrase it?
- `self.0` contains a valid `bindings::poll_table`. - `self.0` is only modified via references to `Self`.
>>> + unsafe { (*ptr)._qproc } >>> + } >>> + >>> + /// Register this [`PollTable`] with the provided [`PollCondVar`], so that it can be notified >>> + /// using the condition variable. >>> + pub fn register_wait(&mut self, file: &File, cv: &PollCondVar) { >>> + if let Some(qproc) = self.get_qproc() { >>> + // SAFETY: The pointers to `self` and `file` are valid because they are references. >> >> What about cv.wait_list... > > I can add it to the list of things that are valid due to references.
Yes this is getting a bit tedious.
What if we create a newtype wrapping `Opaque<T>` with the invariant that it contains a valid value? Then we could have a specially named getter for which we would always assume that the returned pointer is valid. And thus permit you to not mention it in the SAFETY comment?
[...]
>>> +#[pinned_drop] >>> +impl PinnedDrop for PollCondVar { >>> + fn drop(self: Pin<&mut Self>) { >>> + // Clear anything registered using `register_wait`. >>> + // >>> + // SAFETY: The pointer points at a valid wait list. >> >> I was a bit confused by "wait list", since the C type is named >> `wait_queue_head`, maybe just use the type name? > > I will update all instances of "wait list" to "wait_queue_head". It's > because I incorrectly remembered the C type name to be "wait_list".
Maybe we should also change the name of the field on `CondVar`?
If you guys agree, I can open a good-first-issue, since it is a very simple change.
-- Cheers, Benno
| |