Re: [PATCH] rust-next: make from_errno use try_from_errno

[Rasmus Villemoes <ravi@prevas.dk>]

On Tue, Nov 05 2024, Guilherme Augusto Martins da Silva <guilhermev2huehue@gmail.com> wrote:

> Modified the from_errno function to use try_from_errno to reduce code duplication while still maintaning all existing behavior and error handling and also reduces unsafe code.
>
> Co-developed-by: Daniel Sedlak <daniel@sedlak.dev>
> Signed-off-by: Daniel Sedlak <daniel@sedlak.dev>
> Signed-off-by: Guilherme Augusto Martins da Silva <guilhermev2huehue@gmail.com>
> Suggested-by:  Miguel Ojeda <ojeda@kernel.org>
> Link: https://github.com/Rust-for-Linux/linux/issues/1125
> ---
> diff --git a/rust/kernel/error.rs b/rust/kernel/error.rs
> index 7cd3bbab52f2..077f95cbb6ae 100644
> --- a/rust/kernel/error.rs
> +++ b/rust/kernel/error.rs
> @@ -101,19 +101,17 @@ impl Error {
>      /// It is a bug to pass an out-of-range `errno`. `EINVAL` would
>      /// be returned in such a case.
>      pub fn from_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;
> +        match Error::try_from_errno(errno) {
> +            Some(error) => error,
> +            None => {
> +                // TODO: Make it a `WARN_ONCE` once available.
> +                crate::pr_warn!(
> +                    "attempted to create `Error` with out of range `errno`: {}",
> +                    errno
> +                );
> +                code::EINVAL
> +            }


Not really related to the change done here, but I've often wondered why
the kernel doesn't have a dedicated EBUG that can be used in places
where a genuine kernel bug is detected at run-time, but BUG() is too
much, and we can survive by just passing some error back up the stack
(possibly with a WARN or pr_warn()). In fact, an EBUG could be useful in
userspace code as well for library code that detects some
should-not-happen inconsistency.

EINVAL is already way overused, and substituting that when a programming
error rather than bad user input is detected seems to just overload it
even more.

Rasmus