Re: [PATCH] [RFC] rust: error: Convert 0 being an error to Result

[Greg KH <gregkh@linuxfoundation.org>]

On Thu, Jan 11, 2024 at 07:44:15AM +0100, Dirk Behme wrote:
> The existing to_result() takes a (signed) integer from a kernel C function
> and converts it to an error if it's negative. Additionally, there are
> kernel C functions returning an unsigned integer where 0 is the error case.
> For example gen_pool_alloc() and friends. Provide a mechanism to convert
> this to Result too.
> 
> Signed-off-by: Dirk Behme <dirk.behme@de.bosch.com>
> ---
>  rust/kernel/error.rs | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> I'm unsure if something like this is acceptable. Therefore the RFC.
> But I want at least ask ;) In the end this is a slightly modified
> copy of the existing to_result().
> 
> diff --git a/rust/kernel/error.rs b/rust/kernel/error.rs
> index 376280b6a745a..3306b8f590866 100644
> --- a/rust/kernel/error.rs
> +++ b/rust/kernel/error.rs
> @@ -248,6 +248,16 @@ pub fn to_result(err: core::ffi::c_int) -> Result {
>      }
>  }
>  
> +/// Converts an unsigned integer as returned by a C kernel function to EINVAL if it's zero,
> +/// and `Ok(u64)` otherwise.
> +pub fn to_result_zero(val: core::ffi::c_ulong) -> Result<u64> {
> +    if val == 0 {
> +        Err(code::EINVAL)
> +    } else {
> +        Ok(val)
> +    }
> +}

How would this be used?  0 is normally not an error, why would you
need/want to turn that into an error value?

thanks,

greg k-h