linux-kernel - Re: [PATCH v5 6/6] rust: use strict provenance APIs

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Message-ID: <CAJ-ks9kYB1b4XsQcFb=NScPq+R+13U+Sv-6opi-yp6=ZjuLD_g@mail.gmail.com>
Date: Mon, 17 Mar 2025 16:35:42 -0400
From: Tamir Duberstein <tamird@...il.com>
To: Boqun Feng <boqun.feng@...il.com>
Cc: Masahiro Yamada <masahiroy@...nel.org>, Nathan Chancellor <nathan@...nel.org>, 
	Nicolas Schier <nicolas@...sle.eu>, Miguel Ojeda <ojeda@...nel.org>, 
	Alex Gaynor <alex.gaynor@...il.com>, Gary Guo <gary@...yguo.net>, 
	Björn Roy Baron <bjorn3_gh@...tonmail.com>, 
	Benno Lossin <benno.lossin@...ton.me>, Andreas Hindborg <a.hindborg@...nel.org>, 
	Alice Ryhl <aliceryhl@...gle.com>, Trevor Gross <tmgross@...ch.edu>, 
	Danilo Krummrich <dakr@...nel.org>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
	"Rafael J. Wysocki" <rafael@...nel.org>, Brendan Higgins <brendan.higgins@...ux.dev>, 
	David Gow <davidgow@...gle.com>, Rae Moar <rmoar@...gle.com>, 
	Bjorn Helgaas <bhelgaas@...gle.com>, Luis Chamberlain <mcgrof@...nel.org>, 
	Russ Weight <russ.weight@...ux.dev>, Rob Herring <robh@...nel.org>, 
	Saravana Kannan <saravanak@...gle.com>, linux-kbuild@...r.kernel.org, 
	linux-kernel@...r.kernel.org, rust-for-linux@...r.kernel.org, 
	linux-kselftest@...r.kernel.org, kunit-dev@...glegroups.com, 
	linux-pci@...r.kernel.org, linux-block@...r.kernel.org, 
	devicetree@...r.kernel.org
Subject: Re: [PATCH v5 6/6] rust: use strict provenance APIs

On Mon, Mar 17, 2025 at 4:28 PM Boqun Feng <boqun.feng@...il.com> wrote:
>
> On Mon, Mar 17, 2025 at 03:05:45PM -0400, Tamir Duberstein wrote:
> > On Mon, Mar 17, 2025 at 2:50 PM Tamir Duberstein <tamird@...il.com> wrote:
> > >
> > > On Mon, Mar 17, 2025 at 2:17 PM Boqun Feng <boqun.feng@...il.com> wrote:
> > > >
> > > > Then we should fix clippy or how we set msrv rather adding the stub.
> > > > @Miguel?
> > >
> > > I filed https://github.com/rust-lang/rust-clippy/issues/14425.
> >
> > I don't think we can wait for that to be fixed, though. Usually clippy
> > is distributed with rustc via rustup, so even if this is eventually
> > fixed, all versions between 1.84.0 and the fix will need this
> > workaround until MSRV is >= 1.84.0.
>
> We need to take one step back to evalute this "workaround".
>
> First, expose_provenance() and with_exposed_provenance{,_mut}() API are
> clearly defined as equavilent to `as` operation [1]. Therefore, the
> changes in this patch doing the conversion with expose_provenance() and
> with_exposed_provenance{,_mut}() don't change anything related to
> provenance in practice.
>
> I do agree we want to use the explicit provenance API, but I don't think
> we want to introduce some API that we know we will change them latter
> when we bump the rustc minimal version. So the question is: are these
> stubs what we want even though in the future our minimal rustc version
> stablizes provenance API? If not, then the cost of this patch cannot
> justify its benefits IMO.
>
> Now let's also look into why we choose a msrv for clippy, I would guess
> it's because we need to support all the versions of rustc starting at
> 1.78 and we want clippy to report a problem based on 1.78 even though
> we're using a higher version of rustc. But for this particular case, we
> use a feature that has already been stablized in a higher version of
> rustc, which means the problem reported by clippy doesn't help us, nor
> does it provide better code. Frankly speaking, I think we have other
> ways to ensure the support of all rustc versions without a msrv for
> clippy. If I was to choose, I would simply drop the msrv. But maybe I'm
> missing something.
>
> The point is tools should help us to write good and maintainable code,
> we shouldn't introduce complicated structure of code just because some
> tools fail to do its job.
>
> [1]: https://doc.rust-lang.org/std/ptr/fn.with_exposed_provenance_mut.html

Even if we globally disable this clippy lint, we still need stubs
because exposed_provenance was added in 1.79.0. Did your suggestion
address this? Perhaps I missed it.