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Date: Thu, 04 Apr 2024 14:05:57 +0000
To: Alice Ryhl <aliceryhl@google.com>
From: Benno Lossin <benno.lossin@proton.me>
Cc: Miguel Ojeda <ojeda@kernel.org>, Andrew Morton <akpm@linux-foundation.org>, Alex Gaynor <alex.gaynor@gmail.com>, Wedson Almeida Filho <wedsonaf@gmail.com>, Boqun Feng <boqun.feng@gmail.com>, Gary Guo <gary@garyguo.net>, =?utf-8?Q?Bj=C3=B6rn_Roy_Baron?= <bjorn3_gh@protonmail.com>, Andreas Hindborg <a.hindborg@samsung.com>, Marco Elver <elver@google.com>, Kees Cook <keescook@chromium.org>, Coly Li <colyli@suse.de>, Paolo Abeni <pabeni@redhat.com>, Pierre Gondois <pierre.gondois@arm.com>, Ingo Molnar <mingo@kernel.org>, Jakub Kicinski <kuba@kernel.org>, Wei Yang <richard.weiyang@gmail.com>, Matthew Wilcox <willy@infradead.org>, linux-kernel@vger.kernel.org, rust-for-linux@vger.kernel.org
Subject: Re: [PATCH 3/9] rust: list: add struct with prev/next pointers
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On 04.04.24 16:03, Alice Ryhl wrote:
> On Wed, Apr 3, 2024 at 5:57=E2=80=AFPM Benno Lossin <benno.lossin@proton.=
me> wrote:
>>
>> On 02.04.24 14:17, Alice Ryhl wrote:
>>> +/// Implemented by types where a [`ListArc<Self>`] can be inserted int=
o a `List`.
>>> +///
>>> +/// # Safety
>>> +///
>>> +/// Implementers must ensure that they provide the guarantees document=
ed on the three methods
>>> +/// below.
>>> +///
>>> +/// [`ListArc<Self>`]: ListArc
>>> +pub unsafe trait ListItem<const ID: u64 =3D 0>: ListArcSafe<ID> {
>>> +    /// Views the [`ListLinks`] for this value.
>>> +    ///
>>> +    /// # Guarantees
>>> +    ///
>>> +    /// * If there is a currently active call to `prepare_to_insert`, =
then this returns the same
>>> +    ///   pointer as the one returned by the currently active call to =
`prepare_to_insert`.
>>
>> I was a bit confused by the term "active call to `prepare_to_insert`",
>> since I thought that the function would need to be executed at this
>> moment. I inferred from below that you mean by this that there has been
>> a `prepare_to_insert` call, but not yet a corresponding `post_remove`
>> call.
>> I did not yet find a better way to phrase this.
>>
>> I like putting the guarantees on the functions very much.
>=20
> How about this?
>=20
> If there is a previous call to `prepare_to_insert` and there is no
> call to `post_remove` since the most recent such call, then this
> returns the same pointer as the one returned by the most recent call
> to `prepare_to_insert`.
>=20
> Otherwise, the returned pointer points at a read-only [`ListLinks`]
> with two null pointers.
Sounds good.

--=20
Cheers,
Benno