linux-kernel - Re: [PATCH RFC 01/18] rust: drm: ioctl: Add DRM ioctl abstraction

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Date:   Thu, 09 Mar 2023 14:24:25 -0600
From:   Faith Ekstrand <faith.ekstrand@...labora.com>
To:     Asahi Lina <lina@...hilina.net>,
        Björn Roy Baron <bjorn3_gh@...tonmail.com>
Cc:     Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Miguel Ojeda <ojeda@...nel.org>,
        Alex Gaynor <alex.gaynor@...il.com>,
        Wedson Almeida Filho <wedsonaf@...il.com>,
        Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        Christian König <christian.koenig@....com>,
        Luben Tuikov <luben.tuikov@....com>,
        Jarkko Sakkinen <jarkko@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Alyssa Rosenzweig <alyssa@...enzweig.io>,
        Karol Herbst <kherbst@...hat.com>,
        Ella Stanforth <ella@...unix.org>, Mary <mary@...y.zone>,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        rust-for-linux@...r.kernel.org, linux-media@...r.kernel.org,
        linaro-mm-sig@...ts.linaro.org, linux-sgx@...r.kernel.org,
        asahi@...ts.linux.dev
Subject: Re: [PATCH RFC 01/18] rust: drm: ioctl: Add DRM ioctl abstraction

On Thu, 2023-03-09 at 15:04 +0900, Asahi Lina wrote:
> On 08/03/2023 02.34, Björn Roy Baron wrote:
> > > +                            // SAFETY: This is just the ioctl
> > > argument, which hopefully has the right type
> > > +                            // (we've done our best checking the
> > > size).
> > 
> > In the rust tree there is the ReadableFromBytes [1] trait which
> > indicates that it is safe to read arbitrary bytes into the type.
> > Maybe you could add it as bound on the argument type when it lands
> > in rust-next? This way you can't end up with for example a struct
> > containing a bool with the byte value 2, which is UB.
> 
> There's actually a much bigger story here, because that trait isn't
> really very useful without a way to auto-derive it. I need the same
> kind
> of guarantee for all the GPU firmware structs...
> 
> There's one using only declarative macros [1] and one using proc
> macros
> [2]. And then, since ioctl arguments are declared in C UAPI header
> files, we need a way to be able to derive those traits for them...
> which
> I guess means bindgen changes?

It'd be cool to be able to auto-verify that uAPI structs are all
tightly packed and use the right subset of types.  Maybe not possible
this iteration but it'd be cool to see in future.  I'd like to see it
for C as well, ideally.

~Faith