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

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Date:   Tue, 27 Sep 2022 17:43:11 +0200
From:   Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Miguel Ojeda <ojeda@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, patches@...ts.linux.dev,
        Jarkko Sakkinen <jarkko@...nel.org>,
        Wedson Almeida Filho <wedsonaf@...gle.com>,
        Alex Gaynor <alex.gaynor@...il.com>,
        Geoffrey Thomas <geofft@...reload.com>,
        Finn Behrens <me@...enk.de>,
        Adam Bratschi-Kaye <ark.email@...il.com>,
        Sven Van Asbroeck <thesven73@...il.com>,
        Gary Guo <gary@...yguo.net>,
        Boris-Chengbiao Zhou <bobo1239@....de>,
        Boqun Feng <boqun.feng@...il.com>,
        Fox Chen <foxhlchen@...il.com>,
        Viktor Garske <viktor@...ar.de>,
        Dariusz Sosnowski <dsosnowski@...snowski.pl>,
        Léo Lanteri Thauvin <leseulartichaut@...il.com>,
        Niklas Mohrin <dev@...lasmohrin.de>,
        Milan Landaverde <milan@...verde.com>,
        Morgan Bartlett <mjmouse9999@...il.com>,
        Maciej Falkowski <m.falkowski@...sung.com>,
        Nándor István Krácser <bonifaido@...il.com>,
        David Gow <davidgow@...gle.com>,
        John Baublitz <john.m.baublitz@...il.com>,
        Björn Roy Baron <bjorn3_gh@...tonmail.com>
Subject: Re: [PATCH v10 12/27] rust: add `kernel` crate

On Tue, Sep 27, 2022 at 5:22 PM Greg Kroah-Hartman
<gregkh@...uxfoundation.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@...uxfoundation.org>

Thanks a lot for taking a look!

Cheers,
Miguel