References: <20230224-rust-error-v1-0-f8f9a9a87303@asahilina.net>
 <20230224-rust-error-v1-2-f8f9a9a87303@asahilina.net>
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From:   Andreas Hindborg <nmi@metaspace.dk>
To:     Asahi Lina <lina@asahilina.net>
Cc:     Miguel Ojeda <ojeda@kernel.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>,
        Sven Van Asbroeck <thesven73@gmail.com>,
        Fox Chen <foxhlchen@gmail.com>, rust-for-linux@vger.kernel.org,
        linux-kernel@vger.kernel.org, asahi@lists.linux.dev
Subject: Re: [PATCH 2/5] rust: error: Add Error::from_kernel_errno()
Date:   Mon, 27 Feb 2023 14:27:44 +0100
In-reply-to: <20230224-rust-error-v1-2-f8f9a9a87303@asahilina.net>
Message-ID: <87edqb9r08.fsf@metaspace.dk>
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Asahi Lina <lina@asahilina.net> writes:

> From: Miguel Ojeda <ojeda@kernel.org>
>
> Add a function to create `Error` values out of a kernel error return,
> which safely upholds the invariant that the error code is well-formed
> (negative and greater than -MAX_ERRNO). If a malformed code is passed
> in, it will be converted to EINVAL.
>
> Lina: Imported from rust-for-linux/rust as authored by Miguel and Fox
> with refactoring from Wedson.
>
> Co-developed-by: Fox Chen <foxhlchen@gmail.com>
> Signed-off-by: Fox Chen <foxhlchen@gmail.com>
> Co-developed-by: Wedson Almeida Filho <wedsonaf@gmail.com>
> Signed-off-by: Wedson Almeida Filho <wedsonaf@gmail.com>
> Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
> Signed-off-by: Asahi Lina <lina@asahilina.net>
> ---

Reviewed-by: Andreas Hindborg <a.hindborg@samsung.com>

>  rust/kernel/error.rs | 19 +++++++++++++++++++
>  1 file changed, 19 insertions(+)
>
> diff --git a/rust/kernel/error.rs b/rust/kernel/error.rs
> index 8611758e27f4..3b439fdb405c 100644
> --- a/rust/kernel/error.rs
> +++ b/rust/kernel/error.rs
> @@ -72,6 +72,25 @@ pub mod code {
>  pub struct Error(core::ffi::c_int);
>  
>  impl Error {
> +    /// Creates an [`Error`] from a kernel error code.
> +    ///
> +    /// It is a bug to pass an out-of-range `errno`. `EINVAL` would
> +    /// be returned in such a case.
> +    pub(crate) fn from_kernel_errno(errno: core::ffi::c_int) -> Error {
> +        if errno < -(bindings::MAX_ERRNO as i32) || errno >= 0 {
> +            // TODO: Make it a `WARN_ONCE` once available.
> +            crate::pr_warn!(
> +                "attempted to create `Error` with out of range `errno`: {}",
> +                errno
> +            );
> +            return code::EINVAL;
> +        }
> +
> +        // INVARIANT: The check above ensures the type invariant
> +        // will hold.
> +        Error(errno)
> +    }
> +
>      /// Returns the kernel error code.
>      pub fn to_kernel_errno(self) -> core::ffi::c_int {
>          self.0