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

Finn Behrens
2022-11-11T09:51:02Z

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

> From: Wedson Almeida Filho <wedsonaf@gmail.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@gmail.com>
> Signed-off-by: Adam Bratschi-Kaye <ark.email@gmail.com>
> Co-developed-by: Nándor István Krácser <bonifaido@gmail.com>
> Signed-off-by: Nándor István Krácser <bonifaido@gmail.com>
> Signed-off-by: Wedson Almeida Filho <wedsonaf@gmail.com>
> [Reworded, adapted for upstream and applied latest changes]
> Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
Reviewed-by: Finn Behrens <me@kloenk.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