Re: [PATCH v2 3/6] rust: error: Add Error::from_errno()

[Gary Guo <gary@garyguo.net>]

On Wed, 29 Mar 2023 21:04:35 +0900
Asahi Lina <lina@asahilina.net> wrote:

> 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, renamed from_kernel_errno() to
> from_errno().
> 
> 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>
> Reviewed-by: Andreas Hindborg <a.hindborg@samsung.com>
> Signed-off-by: Asahi Lina <lina@asahilina.net>
> ---
>  rust/kernel/error.rs | 19 +++++++++++++++++++
>  1 file changed, 19 insertions(+)
> 
> diff --git a/rust/kernel/error.rs b/rust/kernel/error.rs
> index e97e652a1aec..659468bd1735 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_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_errno(self) -> core::ffi::c_int {
>          self.0
> 

Reviewed-by: Gary Guo <gary@garyguo.net>