linux-kernel - Re: [PATCH 3/3] rust: add WMI abstractions

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Message-ID: <CAC=eVgRHu9UzPyTMcWZFGAwo0+6wO+v-iuqmoKmznj_kSPVL=Q@mail.gmail.com>
Date: Fri, 9 Jan 2026 13:15:22 +0200
From: Kari Argillander <kari.argillander@...il.com>
To: Gladyshev Ilya <foxido@...ido.dev>
Cc: "Rafael J. Wysocki" <rafael@...nel.org>, Len Brown <lenb@...nel.org>, Miguel Ojeda <ojeda@...nel.org>, 
	Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>, 
	Benno Lossin <lossin@...nel.org>, Andreas Hindborg <a.hindborg@...nel.org>, 
	Alice Ryhl <aliceryhl@...gle.com>, Trevor Gross <tmgross@...ch.edu>, 
	Danilo Krummrich <dakr@...nel.org>, Tamir Duberstein <tamird@...il.com>, Armin Wolf <W_Armin@....de>, 
	platform-driver-x86@...r.kernel.org, linux-kernel@...r.kernel.org, 
	rust-for-linux@...r.kernel.org, linux-acpi@...r.kernel.org
Subject: Re: [PATCH 3/3] rust: add WMI abstractions

pe 9.1.2026 klo 13.01 Gladyshev Ilya (foxido@...ido.dev) kirjoitti:
>
> On 1/8/26 23:48, Kari Argillander wrote:
> > On Wed, 7 Jan 2026 at 22:56, Gladyshev Ilya <foxido@...ido.dev> wrote:
> > <snip>
> >
> >> +impl DeviceId {
> >> +    /// Constructs new DeviceId from GUID string.
> >> +    pub const fn new(guid: &[u8; bindings::UUID_STRING_LEN as usize]) -> Self {
> >> +        // SAFETY: FFI type is valid to be zero-initialized.
> >> +        let mut inner: bindings::wmi_device_id = unsafe { MaybeUninit::zeroed().assume_init() };
> >> +
> >> +        build_assert!(inner.guid_string.len() == bindings::UUID_STRING_LEN as usize + 1);
> >> +
> >> +        // SAFETY: It's safe to copy UUID_STRING_LEN, because we validated lengths.
> >> +        // Also we leave last byte zeroed, so guid_string is valid C string.
> >> +        unsafe {
> >> +            ::core::ptr::copy_nonoverlapping(
> >> +                guid.as_ptr(),
> >> +                &raw mut inner.guid_string[0],
> >> +                bindings::UUID_STRING_LEN as usize,
> >> +            );
> >> +        }
> >
> > Just use while here so no unsafe is needed at all. Then probably patch
> > 1/3 is not needed.
>
> Overall this operation is still unsafe because we are constructing C
> string in FFI object. So for me avoiding `unsafe` via less readable
> (imo) loop will just mask unsafe operation without any real benefits.

It is not unsafe if you also use pin_init::zeroed()

        let mut inner: bindings::wmi_device_id = pin_init::zeroed();

        let mut i = 0usize;
        while i < bindings::UUID_STRING_LEN as usize {
            inner.guid_string[i] = guid[i];
            i += 1;
        }

you can then also remove 'core::mem::MaybeUninit'

> Ideally this function should receive c string and just validate it's
> length, but IIRC I had troubles with build-time validation of C string
> length
>
> >> +
> >> +        Self(inner)
> >> +    }
> >> +}