Re: [PATCH v10 12/27] rust: add `kernel` crate

[Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>]

On Tue, Sep 27, 2022 at 5:22 PM Greg Kroah-Hartman
<gregkh@linuxfoundation.org> wrote:
>
> This feels "odd" to me.  Why not just use __kmalloc() instead of
> krealloc()?  I think that will get you the same kasan tracking, and
> should be a tiny bit faster (1-2 less function calls).
>
> I guess it probably doesn't matter right now, just curious, and not a
> big deal at all.

Yeah, nowadays I think a "C helper" could have been used instead.

> You'll be adding other error values here over time, right?

Indeed, I removed all the ones we didn't use in v8 to reduce it a bit
more. Sorry for the confusion! :)

> What about functions that do have return functions of:
>         >= 0 number of bytes read/written/consumed/whatever
>         < 0  error code
>
> Would that use Result or Error as a type?  Or is it best just to not try
> to model that mess in Rust calls? :)

`Result`, i.e. the "number of bytes" part would go in the `Ok` variant
and the "error code" in the `Err` variant.

The benefit is that then you have to handle them "separately", i.e.
you cannot confuse the number of bytes for the error code by mistake,
or vice versa.

> In the long run, using "raw" print macros like this is usually not the
> thing to do.  Drivers always have a device to reference the message to,
> and other things like filesystems and subsystems have a prefix to use as
> well.
>
> Hopefully not many will use these as-is and we can wrap them properly
> later on.

Definitely, we will have e.g. the `dev_*!` ones:

    https://github.com/Rust-for-Linux/linux/blob/fcad53ca9071c7bf6a412640a82e679bad6d1cd4/rust/kernel/device.rs#L479-L502

> Anyway, all looks sane to me, sorry for the noise:
>
> Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Thanks a lot for taking a look!

Cheers,
Miguel