linux-kernel - Re: [PATCH v2 6/6] rust: error: Add from

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Date:   Wed, 29 Mar 2023 11:55:01 -0300
From:   Martin Rodriguez Reboredo <yakoyoku@...il.com>
To:     Asahi Lina <lina@...hilina.net>, Miguel Ojeda <ojeda@...nel.org>,
        Alex Gaynor <alex.gaynor@...il.com>,
        Wedson Almeida Filho <wedsonaf@...il.com>,
        Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>,
        Björn Roy Baron <bjorn3_gh@...tonmail.com>,
        Sven Van Asbroeck <thesven73@...il.com>
Cc:     Fox Chen <foxhlchen@...il.com>,
        Andreas Hindborg <a.hindborg@...sung.com>,
        rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org,
        asahi@...ts.linux.dev
Subject: Re: [PATCH v2 6/6] rust: error: Add from_result() helper

On 3/29/23 09:04, Asahi Lina wrote:
> [...]
> 
> +
> +/// Calls a closure returning a [`crate::error::Result<T>`] and converts the result to
> +/// a C integer result.
> +///
> +/// This is useful when calling Rust functions that return [`crate::error::Result<T>`]
> +/// from inside `extern "C"` functions that need to return an integer error result.
> +///
> +/// `T` should be convertible from an `i16` via `From<i16>`.
> +///
> +/// # Examples
> +///
> +/// ```ignore
> +/// # use kernel::from_result;
> +/// # use kernel::bindings;
> +/// unsafe extern "C" fn probe_callback(
> +///     pdev: *mut bindings::platform_device,
> +/// ) -> core::ffi::c_int {
> +///     from_result(|| {
> +///         let ptr = devm_alloc(pdev)?;
> +///         bindings::platform_set_drvdata(pdev, ptr);
> +///         Ok(0)
> +///     })
> +/// }
> +/// ```
> +// TODO: Remove `dead_code` marker once an in-kernel client is available.
> +#[allow(dead_code)]
> +pub(crate) fn from_result<T, F>(f: F) -> T
> +where
> +    T: From<i16>,
> +    F: FnOnce() -> Result<T>,
> +{
> +    match f() {
> +        Ok(v) => v,
> +        // NO-OVERFLOW: negative `errno`s are no smaller than `-bindings::MAX_ERRNO`,
> +        // `-bindings::MAX_ERRNO` fits in an `i16` as per invariant above,
> +        // therefore a negative `errno` always fits in an `i16` and will not overflow.
> +        Err(e) => T::from(e.to_errno() as i16),
> +    }
> +}
> 

Reviewed-by: Martin Rodriguez Reboredo