linux-kernel - Re: [v4,1/2] rust/revocable: add try_access

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Message-ID: <174469184533.110.4333293420825189955@patchwork.local>
Date: Tue, 15 Apr 2025 04:37:25 -0000
From: Joel Fernandes <joelagnelf@...dia.com>
To: Alexandre Courbot <acourbot@...dia.com>
Cc: Miguel Ojeda <ojeda@...nel.org>, Alex Gaynor <alex.gaynor@...il.com>, Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>, Danilo Krummrich <dakr@...nel.org>, Björn Roy Baron <bjorn3_gh@...tonmail.com>, Benno Lossin <benno.lossin@...ton.me>, Andreas Hindborg <a.hindborg@...nel.org>, Alice Ryhl <aliceryhl@...gle.com>, Trevor Gross <tmgross@...ch.edu>, Bjorn Helgaas <bhelgaas@...gle.com>, rust-for-linux <rust-for-linux@...r.kernel.org>, linux-kernel <linux-kernel@...r.kernel.org>, linux-pci <linux-pci@...r.kernel.org>
Subject: Re: [v4,1/2] rust/revocable: add try_access_with() convenience method

Hello, Alexandre,

On Tue, 15 Apr 2025 04:37:01 GMT, Alexandre Courbot wrote:
> Revocable::try_access() returns a guard through which the wrapped object
> can be accessed. Code that can sleep is not allowed while the guard is
> held; thus, it is common for the caller to explicitly drop it before
> running sleepable code, e.g:
> 
>     let b = bar.try_access()?;
>     let reg = b.readl(...);
> 
>     // Don't forget this or things could go wrong!
>     drop(b);
> 
>     something_that_might_sleep();
> 
>     let b = bar.try_access()?;
>     let reg2 = b.readl(...);
> 
> This is arguably error-prone. try_access_with() provides an arguably
> safer alternative, by taking a closure that is run while the guard is
> held, and by dropping the guard automatically after the closure
> completes. This way, code can be organized more clearly around the
> critical sections and the risk of forgetting to release the guard when
> needed is considerably reduced:
> 
>     let reg = bar.try_access_with(|b| b.readl(...))?;
> 
>     something_that_might_sleep();
> 
>     let reg2 = bar.try_access_with(|b| b.readl(...))?;
> 
> The closure can return nothing, or any value including a Result which is
> then wrapped inside the Option returned by try_access_with. Error
> management is driver-specific, so users are encouraged to create their
> own macros that map and flatten the returned values to something
> appropriate for the code they are working on.
> 
> Acked-by: Danilo Krummrich <dakr@...nel.org>
> Suggested-by: Danilo Krummrich <dakr@...nel.org>
> Reviewed-by: Benno Lossin <benno.lossin@...ton.me>
> Signed-off-by: Alexandre Courbot <acourbot@...dia.com>

Reviewed-by: Joel Fernandes <joelagnelf@...dia.com>

Thanks.