linux-kernel - Re: [PATCH 2/2] rust: alloc: add `Vec::dec

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Message-ID: <D8IPSWQWM6U0.1VLTOFNL99G64@proton.me>
Date: Mon, 17 Mar 2025 17:24:55 +0000
From: Benno Lossin <benno.lossin@...ton.me>
To: Tamir Duberstein <tamird@...il.com>
Cc: Danilo Krummrich <dakr@...nel.org>, Andrew Ballance <andrewjballance@...il.com>, Alice Ryhl <aliceryhl@...gle.com>, Miguel Ojeda <ojeda@...nel.org>, Alex Gaynor <alex.gaynor@...il.com>, 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>, rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] rust: alloc: add `Vec::dec_len`

On Mon Mar 17, 2025 at 4:37 PM CET, Tamir Duberstein wrote:
> On Mon, Mar 17, 2025 at 10:39 AM Benno Lossin <benno.lossin@...ton.me> wrote:
>> On Mon Mar 17, 2025 at 12:34 PM CET, Tamir Duberstein wrote:
>> > On Mon, Mar 17, 2025 at 6:04 AM Benno Lossin <benno.lossin@...ton.me> wrote:
>> >> On Sun Mar 16, 2025 at 11:32 PM CET, Tamir Duberstein wrote:
>> >> > +    ///
>> >> > +    /// # Safety
>> >> > +    ///
>> >> > +    /// - `count` must be less than or equal to `self.len`.
>> >>
>> >> I also think that we should use saturating_sub instead and then not have
>> >> to worry about this. (It should still be documented in the function
>> >> though). That way this can also be a safe function.
>> >
>> > This doesn't seem better to me. I'd prefer to have more rather than
>> > fewer guardrails on such low-level operations.
>>
>> Your second sentence seems like an argument for making it safe? I think
>> it's a lot better as a safe function.
>
> The guardrail I was referring to is the requirement that the caller
> write a safety comment.

But saturating_sub is a better guardrail?

---
Cheers,
Benno