[RFC PATCH 7/8] rust: add firmware abstractions

[Philipp Stanner]

On Wed, 2024-05-22 at 08:53 +0900, FUJITA Tomonori wrote:
> Hi,
> Thanks for working on the firmware API!
> 
> On Mon, 20 May 2024 19:24:19 +0200
> Danilo Krummrich <dakr at redhat.com> wrote:
> 
> > Add an abstraction around the kernels firmware API to request
> > firmware
> > images. The abstraction provides functions to access the firmware
> > buffer and / or copy it to a new buffer allocated with a given
> > allocator
> > backend.
> > 
> > The firmware is released once the abstraction is dropped.
> > 
> > Signed-off-by: Danilo Krummrich <dakr at redhat.com>
> > ---
> >   rust/bindings/bindings_helper.h |  1 +
> >   rust/kernel/firmware.rs         | 74
> > +++++++++++++++++++++++++++++++++
> >   rust/kernel/lib.rs              |  1 +
> >   3 files changed, 76 insertions(+)
> >   create mode 100644 rust/kernel/firmware.rs
> > 
> > diff --git a/rust/bindings/bindings_helper.h
> > b/rust/bindings/bindings_helper.h
> > index b245db8d5a87..e4ffc47da5ec 100644
> > --- a/rust/bindings/bindings_helper.h
> > +++ b/rust/bindings/bindings_helper.h
> > @@ -14,6 +14,7 @@
> >   #include <kunit/test.h>
> >   #include <linux/errname.h>
> >   #include <linux/ethtool.h>
> > +#include <linux/firmware.h>
> >   #include <linux/jiffies.h>
> >   #include <linux/mdio.h>
> >   #include <linux/pci.h>
> > diff --git a/rust/kernel/firmware.rs b/rust/kernel/firmware.rs
> > new file mode 100644
> > index 000000000000..700504fb3c9c
> > --- /dev/null
> > +++ b/rust/kernel/firmware.rs
> > @@ -0,0 +1,74 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +
> > +//! Firmware abstraction
> > +//!
> > +//! C header:
> > [`include/linux/firmware.h`](../../../../include/linux/firmware.h")
> > +
> > +use crate::{bindings, device::Device, error::Error, error::Result,
> > str::CStr, types::Opaque};
> > +
> > +/// Abstraction around a C firmware struct.
> > +///
> > +/// This is a simple abstraction around the C firmware API. Just
> > like with the C API, firmware can
> > +/// be requested. Once requested the abstraction provides direct
> > access to the firmware buffer as
> > +/// `&[u8]`. Alternatively, the firmware can be copied to a new
> > buffer using `Firmware::copy`. The
> > +/// firmware is released once [`Firmware`] is dropped.
> > +///
> > +/// # Examples
> > +///
> > +/// ```
> > +/// let fw = Firmware::request("path/to/firmware.bin",
> > dev.as_ref())?;
> > +/// driver_load_firmware(fw.data());
> > +/// ```
> > +pub struct Firmware(Opaque<*const bindings::firmware>);
> 
> Wrapping a raw pointer is not the intended use of Qpaque type?
> 

What is the intended use?
As I see it, all uses wrapp some binding::* – but a rawpointer to a
binding shouldn't be wrapped by it?

Maybe we can add something to the docu in kernel/types.rs:


/// Stores an opaque value.
///
/// This is meant to be used with FFI objects that are never interpreted by Rust code.
#[repr(transparent)]
pub struct Opaque<T> {



P.