Re: [PATCH v7 03/16] rust: implement `IdArray`, `IdTable` and `RawDeviceId`

Danilo Krummrich
2025-01-02T09:36:36Z

On Tue, Dec 24, 2024 at 08:10:02PM +0000, Gary Guo wrote:
> On Thu, 19 Dec 2024 18:04:05 +0100
> Danilo Krummrich <dakr@kernel.org> wrote:
>
> > Most subsystems use some kind of ID to match devices and drivers. Hence,
> > we have to provide Rust drivers an abstraction to register an ID table
> > for the driver to match.
> >
> > Generally, those IDs are subsystem specific and hence need to be
> > implemented by the corresponding subsystem. However, the `IdArray`,
> > `IdTable` and `RawDeviceId` types provide a generalized implementation
> > that makes the life of subsystems easier to do so.
> >
> > Co-developed-by: Wedson Almeida Filho <wedsonaf@gmail.com>
> > Signed-off-by: Wedson Almeida Filho <wedsonaf@gmail.com>
> > Co-developed-by: Gary Guo <gary@garyguo.net>
> > Signed-off-by: Gary Guo <gary@garyguo.net>
> > Co-developed-by: Fabien Parent <fabien.parent@linaro.org>
> > Signed-off-by: Fabien Parent <fabien.parent@linaro.org>
> > Signed-off-by: Danilo Krummrich <dakr@kernel.org>
>
> Thank you for converting my prototype to a working patch. There's a nit below.
>
> > ---
> > MAINTAINERS | 1 +
> > rust/kernel/device_id.rs | 165 +++++++++++++++++++++++++++++++++++++++
> > rust/kernel/lib.rs | 6 ++
> > 3 files changed, 172 insertions(+)
> > create mode 100644 rust/kernel/device_id.rs
> >
> > diff --git a/MAINTAINERS b/MAINTAINERS
> > index 2ad58ed40079..3cfb68650347 100644
> > --- a/MAINTAINERS
> > +++ b/MAINTAINERS
> > @@ -7033,6 +7033,7 @@ F: include/linux/kobj*
> > F: include/linux/property.h
> > F: lib/kobj*
> > F: rust/kernel/device.rs
> > +F: rust/kernel/device_id.rs
> > F: rust/kernel/driver.rs
> >
> > DRIVERS FOR OMAP ADAPTIVE VOLTAGE SCALING (AVS)
> > diff --git a/rust/kernel/device_id.rs b/rust/kernel/device_id.rs
> > new file mode 100644
> > index 000000000000..e5859217a579
> > --- /dev/null
> > +++ b/rust/kernel/device_id.rs
> >
> > <snip>
> >
> > +
> > +impl<T: RawDeviceId, const N: usize> RawIdArray<T, N> {
> > + #[doc(hidden)]
> > + pub const fn size(&self) -> usize {
> > + core::mem::size_of::<Self>()
> > + }
> > +}
> > +
>
> This is not necessary, see below.
>
> > <snip>
> >
> > +
> > +/// Create device table alias for modpost.
> > +#[macro_export]
> > +macro_rules! module_device_table {
> > + ($table_type: literal, $module_table_name:ident, $table_name:ident) => {
> > + #[rustfmt::skip]
> > + #[export_name =
> > + concat!("__mod_device_table__", $table_type,
> > + "__", module_path!(),
> > + "_", line!(),
> > + "_", stringify!($table_name))
> > + ]
> > + static $module_table_name: [core::mem::MaybeUninit<u8>; $table_name.raw_ids().size()] =
> > + unsafe { core::mem::transmute_copy($table_name.raw_ids()) };
>
> const_size_of_val will be stable in Rust 1.85, so we can start using the
> feature and
>
> static $module_table_name: [core::mem::MaybeUninit<u8>; core::mem::size_of_val($table_name.raw_ids())] =
> unsafe { core::mem::transmute_copy($table_name.raw_ids()) };
>
> should work.

Thanks for the note, this indeed saves a few lines.

Since the series has been applied already, feel free to send a patch.

>
> > + };
> > +}
> > diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
> > index 7818407f9aac..66149ac5c0c9 100644
> > --- a/rust/kernel/lib.rs
> > +++ b/rust/kernel/lib.rs
> > @@ -18,6 +18,11 @@
> > #![feature(inline_const)]
> > #![feature(lint_reasons)]
> > #![feature(unsize)]
> > +// Stable in Rust 1.83
> > +#![feature(const_maybe_uninit_as_mut_ptr)]
> > +#![feature(const_mut_refs)]
> > +#![feature(const_ptr_write)]
> > +#![feature(const_refs_to_cell)]
> >
> > // Ensure conditional compilation based on the kernel configuration works;
> > // otherwise we may silently break things like initcall handling.
> > @@ -35,6 +40,7 @@
> > mod build_assert;
> > pub mod cred;
> > pub mod device;
> > +pub mod device_id;
> > pub mod driver;
> > pub mod error;
> > #[cfg(CONFIG_RUST_FW_LOADER_ABSTRACTIONS)]
>