linux-kernel - Re: [PATCH v1 10/28] rust: error: add `From` implementations for `Error`

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Date:   Fri, 11 Nov 2022 10:50:51 +0100
From:   Finn Behrens <me@...enk.dev>
To:     Miguel Ojeda <ojeda@...nel.org>
Cc:     Wedson Almeida Filho <wedsonaf@...il.com>,
        Alex Gaynor <alex.gaynor@...il.com>,
        Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>,
        Björn Roy Baron <bjorn3_gh@...tonmail.com>,
        rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org,
        patches@...ts.linux.dev, Adam Bratschi-Kaye <ark.email@...il.com>,
        Nándor István Krácser <bonifaido@...il.com>
Subject: Re: [PATCH v1 10/28] rust: error: add `From` implementations for
 `Error`

On 10 Nov 2022, at 17:41, Miguel Ojeda wrote:

> From: Wedson Almeida Filho <wedsonaf@...il.com>
>
> Add a set of `From` implementations for the `Error` kernel type.
>
> These implementations allow to easily convert from standard Rust
> error types to the usual kernel errors based on one of the `E*`
> integer codes.
>
> On top of that, the question mark Rust operator (`?`) implicitly
> performs a conversion on the error value using the `From` trait
> when propagating. Thus it is extra convenient to use.
>
> For instance, a kernel function that needs to convert a `i64` into
> a `i32` and to bubble up the error as a kernel error may write:
>
>     fn f(x: i64) -> Result<...> {
>         ...
>         let y = i32::try_from(x)?;
>         ...
>     }
>
> which will transform the `TryFromIntError` into an `Err(EINVAL)`.
>
> Co-developed-by: Adam Bratschi-Kaye <ark.email@...il.com>
> Signed-off-by: Adam Bratschi-Kaye <ark.email@...il.com>
> Co-developed-by: Nándor István Krácser <bonifaido@...il.com>
> Signed-off-by: Nándor István Krácser <bonifaido@...il.com>
> Signed-off-by: Wedson Almeida Filho <wedsonaf@...il.com>
> [Reworded, adapted for upstream and applied latest changes]
> Signed-off-by: Miguel Ojeda <ojeda@...nel.org>
Reviewed-by: Finn Behrens <me@...enk.dev>

Regards,
Finn
> ---
>  rust/kernel/error.rs | 45 +++++++++++++++++++++++++++++++++++++++++++-
>  rust/kernel/lib.rs   |  1 +
>  2 files changed, 45 insertions(+), 1 deletion(-)
>
> diff --git a/rust/kernel/error.rs b/rust/kernel/error.rs
> index 861746f2422d..5b9751d7ff1d 100644
> --- a/rust/kernel/error.rs
> +++ b/rust/kernel/error.rs
> @@ -4,7 +4,14 @@
>  //!
>  //! C header: [`include/uapi/asm-generic/errno-base.h`](../../../include/uapi/asm-generic/errno-base.h)
>
> -use alloc::collections::TryReserveError;
> +use alloc::{
> +    alloc::{AllocError, LayoutError},
> +    collections::TryReserveError,
> +};
> +
> +use core::convert::From;
> +use core::num::TryFromIntError;
> +use core::str::Utf8Error;
>
>  /// Contains the C-compatible error codes.
>  pub mod code {
> @@ -71,12 +78,48 @@ impl Error {
>      }
>  }
>
> +impl From<AllocError> for Error {
> +    fn from(_: AllocError) -> Error {
> +        code::ENOMEM
> +    }
> +}
> +
> +impl From<TryFromIntError> for Error {
> +    fn from(_: TryFromIntError) -> Error {
> +        code::EINVAL
> +    }
> +}
> +
> +impl From<Utf8Error> for Error {
> +    fn from(_: Utf8Error) -> Error {
> +        code::EINVAL
> +    }
> +}
> +
>  impl From<TryReserveError> for Error {
>      fn from(_: TryReserveError) -> Error {
>          code::ENOMEM
>      }
>  }
>
> +impl From<LayoutError> for Error {
> +    fn from(_: LayoutError) -> Error {
> +        code::ENOMEM
> +    }
> +}
> +
> +impl From<core::fmt::Error> for Error {
> +    fn from(_: core::fmt::Error) -> Error {
> +        code::EINVAL
> +    }
> +}
> +
> +impl From<core::convert::Infallible> for Error {
> +    fn from(e: core::convert::Infallible) -> Error {
> +        match e {}
> +    }
> +}
> +
>  /// A [`Result`] with an [`Error`] error type.
>  ///
>  /// To be used as the return type for functions that may fail.
> diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
> index abd46261d385..ffc6626a6d29 100644
> --- a/rust/kernel/lib.rs
> +++ b/rust/kernel/lib.rs
> @@ -12,6 +12,7 @@
>  //! do so first instead of bypassing this crate.
>
>  #![no_std]
> +#![feature(allocator_api)]
>  #![feature(core_ffi_c)]
>
>  // Ensure conditional compilation based on the kernel configuration works;
> -- 
> 2.38.1