linux-kernel - Re: [PATCH v2 3/4] rust: pci: impl TryFrom<&Device> for &pci::Device

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Message-ID: <CANiq72nvp_fWD6oDULgq1PVBD417iUVVWcZr_cvfd8r9Lpk=rg@mail.gmail.com>
Date: Fri, 21 Mar 2025 20:37:47 +0100
From: Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
To: Danilo Krummrich <dakr@...nel.org>
Cc: kernel test robot <lkp@...el.com>, bhelgaas@...gle.com, gregkh@...uxfoundation.org, 
	rafael@...nel.org, ojeda@...nel.org, alex.gaynor@...il.com, 
	boqun.feng@...il.com, gary@...yguo.net, bjorn3_gh@...tonmail.com, 
	benno.lossin@...ton.me, a.hindborg@...nel.org, aliceryhl@...gle.com, 
	tmgross@...ch.edu, llvm@...ts.linux.dev, oe-kbuild-all@...ts.linux.dev, 
	linux-pci@...r.kernel.org, rust-for-linux@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 3/4] rust: pci: impl TryFrom<&Device> for &pci::Device

On Fri, Mar 21, 2025 at 8:11 PM Danilo Krummrich <dakr@...nel.org> wrote:
>
> From the second link:
>
> "Previously, the compiler's safety checks were not aware that the raw ref
> operator did not actually affect the operand's place, treating it as a possible
> read or write to a pointer. No unsafety is actually present, however, as it just
> creates a pointer.
>
> That sounds like it was a bug, or do I miss anything?

Yeah, if they didn't intend it originally, then I would call it a bug
-- they also seemed to considered it a bug themselves in the end, so I
think you are right.

I meant it from the point of view of the language, i.e. in the sense
that it was a restriction before, and now they relaxed it, so more
programs are accepted, and the feature would be "you need less
`unsafe`" etc.

The blog post seems to mention both sides of the coin ("This code is
now allowed", "Relaxed this", "A future version of Rust is expected to
generalize this").

> Yeah, thanks a lot. Especially for the second link, I couldn't find it even
> after quite a while of searching.

You're welcome!

Cheers,
Miguel