linux-kernel - Re: [PATCH] poll: rust: allow poll

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Message-Id: <DASWBTM3280H.KMIP372JNU2O@kernel.org>
Date: Sun, 22 Jun 2025 09:50:15 +0200
From: "Benno Lossin" <lossin@...nel.org>
To: "Alice Ryhl" <aliceryhl@...gle.com>
Cc: "Alexander Viro" <viro@...iv.linux.org.uk>, "Jan Kara" <jack@...e.cz>,
 "Miguel Ojeda" <ojeda@...nel.org>, "Christian Brauner"
 <brauner@...nel.org>, "Boqun Feng" <boqun.feng@...il.com>, "Gary Guo"
 <gary@...yguo.net>, Björn Roy Baron
 <bjorn3_gh@...tonmail.com>, "Andreas Hindborg" <a.hindborg@...nel.org>,
 "Trevor Gross" <tmgross@...ch.edu>, "Danilo Krummrich" <dakr@...nel.org>,
 <linux-kernel@...r.kernel.org>, <rust-for-linux@...r.kernel.org>
Subject: Re: [PATCH] poll: rust: allow poll_table ptrs to be null

On Fri Jun 20, 2025 at 3:19 PM CEST, Alice Ryhl wrote:
> On Fri, Jun 20, 2025 at 2:31 PM Benno Lossin <lossin@...nel.org> wrote:
>>
>> On Fri Jun 20, 2025 at 1:49 PM CEST, Alice Ryhl wrote:
>> >      ///
>> >      /// # Safety
>> >      ///
>> > -    /// The caller must ensure that for the duration of `'a`, the pointer will point at a valid poll
>> > -    /// table (as defined in the type invariants).
>> > -    ///
>> > -    /// The caller must also ensure that the `poll_table` is only accessed via the returned
>> > -    /// reference for the duration of `'a`.
>> > -    pub unsafe fn from_ptr<'a>(ptr: *mut bindings::poll_table) -> &'a mut PollTable {
>>
>> Returning `Option<&'a mut PollTable>` is not an option? I'd like to
>> avoid wrapping raw pointers...
>
> You're going to make people handle the Option by early-returning if
> you do that, but that's wrong. You're supposed to treat null and
> non-null the same.

Ah right...

An `PollTableInner` type that wraps the `bindings::poll_table` opaquely
sounds like too much work, so let's go with your approach.

---
Cheers,
Benno