linux-kernel - Re: [PATCH v1 2/2] rust: Add read_poll

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Message-Id: <20250817.132133.2247398178715604981.fujita.tomonori@gmail.com>
Date: Sun, 17 Aug 2025 13:21:33 +0900 (JST)
From: FUJITA Tomonori <fujita.tomonori@...il.com>
To: aliceryhl@...gle.com
Cc: a.hindborg@...nel.org, alex.gaynor@...il.com, ojeda@...nel.org,
 anna-maria@...utronix.de, bjorn3_gh@...tonmail.com, boqun.feng@...il.com,
 dakr@...nel.org, frederic@...nel.org, gary@...yguo.net,
 jstultz@...gle.com, linux-kernel@...r.kernel.org, lossin@...nel.org,
 lyude@...hat.com, rust-for-linux@...r.kernel.org, sboyd@...nel.org,
 tglx@...utronix.de, tmgross@...ch.edu, acourbot@...dia.com,
 daniel.almeida@...labora.com, me@...enk.dev
Subject: Re: [PATCH v1 2/2] rust: Add read_poll_timeout functions

On Thu, 14 Aug 2025 15:11:47 +0900 (JST)
FUJITA Tomonori <fujita.tomonori@...il.com> wrote:

>>> +#[track_caller]
>>> +pub fn read_poll_timeout<Op, Cond, T>(
>>> +    mut op: Op,
>>> +    mut cond: Cond,
>>> +    sleep_delta: Delta,
>>> +    timeout_delta: Option<Delta>,
>>> +) -> Result<T>
>>> +where
>>> +    Op: FnMut() -> Result<T>,
>>> +    Cond: FnMut(&T) -> bool,
>> 
>> I would consider just writing this as:
>>
>> pub fn read_poll_timeout<T>(
>>     mut op: impl FnMut() -> Result<T>,
>>     mut cond: impl FnMut(&T) -> bool,
>>     sleep_delta: Delta,
>>     timeout_delta: Option<Delta>,
>> ) -> Result<T>
> 
> Surely, I'll do.

The above change caused the example code to fail to compile with a
"type annotations needed" error, so I kept the original code.


>> And I would also consider adding a new error type called TimeoutError
>> similar to BadFdError in `rust/kernel/fs/file.rs`. That way, we promise
>> to the caller that we never return error codes other than a timeout.
> 
> Understood, I'll.

I was reminded that this function can return errors other than
timeout; Op closure returns an any error like register read failure.