linux-kernel - Re: [PATCH v12 1/3] rust: io: add resource abstraction

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Message-ID: <CAH5fLghe0-s2SQ+_cwNmagw8depC+=6kUwUm_epLFz30k9gQJw@mail.gmail.com>
Date: Thu, 10 Jul 2025 15:40:01 +0200
From: Alice Ryhl <aliceryhl@...gle.com>
To: Daniel Almeida <daniel.almeida@...labora.com>
Cc: 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>, 
	Andreas Hindborg <a.hindborg@...nel.org>, Trevor Gross <tmgross@...ch.edu>, 
	Danilo Krummrich <dakr@...nel.org>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
	"Rafael J. Wysocki" <rafael@...nel.org>, Andrew Morton <akpm@...ux-foundation.org>, 
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>, 
	Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>, 
	Bjorn Helgaas <bhelgaas@...gle.com>, Mika Westerberg <mika.westerberg@...ux.intel.com>, 
	Ying Huang <huang.ying.caritas@...il.com>, Benno Lossin <lossin@...nel.org>, 
	linux-kernel@...r.kernel.org, rust-for-linux@...r.kernel.org, 
	Fiona Behrens <me@...enk.dev>
Subject: Re: [PATCH v12 1/3] rust: io: add resource abstraction

On Thu, Jul 10, 2025 at 3:34 PM Daniel Almeida
<daniel.almeida@...labora.com> wrote:
>
> […]
>
> >
> >> +    }
> >> +
> >> +    /// Returns the name of the resource.
> >> +    pub fn name(&self) -> &'static CStr {
> >> +        let inner = self.0.get();
> >> +        // SAFETY: safe as per the invariants of `Resource`
> >> +        unsafe { CStr::from_char_ptr((*inner).name) }
> >> +    }
> >> +
> >> +    /// Returns the flags associated with the resource.
> >> +    pub fn flags(&self) -> Flags {
> >> +        let inner = self.0.get();
> >> +        // SAFETY: safe as per the invariants of `Resource`
> >> +        let flags = unsafe { *inner }.flags;
> >> +
> >> +        Flags(flags)
> >> +    }
> >> +}
> >> +
> >> +// SAFETY: `Resource` only holds a pointer to a C `struct resource`, which is
> >> +// safe to be used from any thread.
> >> +unsafe impl Send for Resource {}
> >> +
> >> +// SAFETY: `Resource` only holds a pointer to a C `struct resource`, references
> >> +// to which are safe to be used from any thread.
> >> +unsafe impl Sync for Resource {}
> >> +
> >> +/// Resource flags as stored in the C `struct resource::flags` field.
> >> +///
> >> +/// They can be combined with the operators `|`, `&`, and `!`.
> >> +///
> >> +/// Values can be used from the [`flags`] module.
> >> +#[derive(Clone, Copy, PartialEq)]
> >> +pub struct Flags(usize);
> >
> > Based on usage it looks like the correct type is c_int?
>
> Shouldn’t this be c_ulong because of:
>
> #[repr(C)]
> #[derive(Copy, Clone)]
> pub struct resource {
>     pub start: resource_size_t,
>     pub end: resource_size_t,
>     pub name: *const ffi::c_char,
>     pub flags: ffi::c_ulong, <——
>
> In any case, we will have to cast this because __request_region
> expects c_int.

I saw that you called a C function that expects an int, so that's why
I suggested c_int. It sounds like the cast from int to long happens in
C code.

Alice