linux-kernel - Re: [PATCH V6 04/15] rust: device: Add few helpers

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Message-ID: <CAH5fLgg+XQ2ALpW2x2Mwc4h-ZMo8ZpynH3VA9kxFWyg5SgvmXw@mail.gmail.com>
Date: Wed, 8 Jan 2025 12:55:38 +0100
From: Alice Ryhl <aliceryhl@...gle.com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Viresh Kumar <viresh.kumar@...aro.org>, "Rafael J. Wysocki" <rafael@...nel.org>, 
	Miguel Ojeda <miguel.ojeda.sandonis@...il.com>, Danilo Krummrich <dakr@...hat.com>, 
	Miguel Ojeda <ojeda@...nel.org>, Alex Gaynor <alex.gaynor@...il.com>, 
	Boqun Feng <boqun.feng@...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>, 
	Trevor Gross <tmgross@...ch.edu>, Danilo Krummrich <dakr@...nel.org>, linux-pm@...r.kernel.org, 
	Vincent Guittot <vincent.guittot@...aro.org>, Stephen Boyd <sboyd@...nel.org>, 
	Nishanth Menon <nm@...com>, rust-for-linux@...r.kernel.org, 
	Manos Pitsidianakis <manos.pitsidianakis@...aro.org>, Erik Schilling <erik.schilling@...aro.org>, 
	Alex Bennée <alex.bennee@...aro.org>, 
	Joakim Bech <joakim.bech@...aro.org>, Rob Herring <robh@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH V6 04/15] rust: device: Add few helpers

On Wed, Jan 8, 2025 at 12:52 PM Greg Kroah-Hartman
<gregkh@...uxfoundation.org> wrote:
> > +    /// Checks if property is present or not.
> > +    pub fn property_present(&self, name: &CString) -> bool {
> > +        // SAFETY: By the invariant of `CString`, `name` is null-terminated.
> > +        unsafe { bindings::device_property_present(self.as_raw() as *const _, name.as_ptr() as *const _) }
>
> I hate to ask, but how was this compiling if the const wasn't there
> before?  There's no type-checking happening here?  If not, how are we
> ever going to notice when function parameters change?  If there is type
> checking, how did this ever build without the const?
>
> confused,

Rust auto-converts `*mut` pointers to `*const` when necessary.

Note that this should really be `self.as_raw().cast_const()` if you're
just casting mut to const without changing the pointee type.

Alice