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Date: Mon, 17 Jun 2024 15:05:32 -0700
From: Boqun Feng <boqun.feng@...il.com>
To: Danilo Krummrich <dakr@...hat.com>
Cc: gregkh@...uxfoundation.org, rafael@...nel.org, mcgrof@...nel.org,
russ.weight@...ux.dev, ojeda@...nel.org, alex.gaynor@...il.com,
wedsonaf@...il.com, gary@...yguo.net, bjorn3_gh@...tonmail.com,
benno.lossin@...ton.me, a.hindborg@...sung.com,
aliceryhl@...gle.com, airlied@...il.com, fujita.tomonori@...il.com,
pstanner@...hat.com, ajanulgu@...hat.com, lyude@...hat.com,
rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 2/2] rust: add firmware abstractions
On Mon, Jun 17, 2024 at 10:29:41PM +0200, Danilo Krummrich wrote:
> Add an abstraction around the kernels firmware API to request firmware
> images. The abstraction provides functions to access the firmware's size
> and backing buffer.
>
> The firmware is released once the abstraction instance is dropped.
>
> Signed-off-by: Danilo Krummrich <dakr@...hat.com>
> ---
> drivers/base/firmware_loader/Kconfig | 7 ++
> rust/bindings/bindings_helper.h | 1 +
> rust/kernel/firmware.rs | 98 ++++++++++++++++++++++++++++
> rust/kernel/lib.rs | 2 +
> 4 files changed, 108 insertions(+)
> create mode 100644 rust/kernel/firmware.rs
>
> diff --git a/drivers/base/firmware_loader/Kconfig b/drivers/base/firmware_loader/Kconfig
> index 5ca00e02fe82..a03701674265 100644
> --- a/drivers/base/firmware_loader/Kconfig
> +++ b/drivers/base/firmware_loader/Kconfig
> @@ -37,6 +37,13 @@ config FW_LOADER_DEBUG
> SHA256 checksums to the kernel log for each firmware file that is
> loaded.
>
> +config RUST_FW_LOADER_ABSTRACTIONS
> + bool "Rust Firmware Loader abstractions"
> + depends on RUST
> + depends on FW_LOADER=y
> + help
> + This enables the Rust abstractions for the firmware loader API.
> +
> if FW_LOADER
>
> config FW_LOADER_PAGED_BUF
> diff --git a/rust/bindings/bindings_helper.h b/rust/bindings/bindings_helper.h
> index ddb5644d4fd9..18a3f05115cb 100644
> --- a/rust/bindings/bindings_helper.h
> +++ b/rust/bindings/bindings_helper.h
> @@ -9,6 +9,7 @@
> #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/phy.h>
> diff --git a/rust/kernel/firmware.rs b/rust/kernel/firmware.rs
> new file mode 100644
> index 000000000000..05a4f84cfd42
> --- /dev/null
> +++ b/rust/kernel/firmware.rs
> @@ -0,0 +1,98 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +//! Firmware abstraction
> +//!
> +//! C header: [`include/linux/firmware.h`](srctree/include/linux/firmware.h")
> +
> +use crate::{bindings, device::Device, error::Error, error::Result, str::CStr};
> +use core::ptr::NonNull;
> +
> +// One of the following: `bindings::request_firmware`, `bindings::firmware_request_nowarn`,
> +// `firmware_request_platform`, `bindings::request_firmware_direct`
> +type FwFunc =
> + unsafe extern "C" fn(*mut *const bindings::firmware, *const i8, *mut bindings::device) -> i32;
> +
> +/// Abstraction around a C `struct firmware`.
> +///
> +/// 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]`. The firmware is released once [`Firmware`] is dropped.
> +///
> +/// # Invariants
> +///
> +/// The pointer is valid, and has ownership over the instance of `struct firmware`.
> +///
> +/// # Examples
> +///
> +/// ```
> +/// # use kernel::{c_str, device::Device, firmware::Firmware};
> +///
> +/// # // SAFETY: *NOT* safe, just for the example to get an `ARef<Device>` instance
> +/// # let dev = unsafe { Device::from_raw(core::ptr::null_mut()) };
> +///
> +/// let fw = Firmware::request(c_str!("path/to/firmware.bin"), &dev).unwrap();
> +/// let blob = fw.data();
> +/// ```
> +pub struct Firmware(NonNull<bindings::firmware>);
> +
I feel like eventually we need a very simple smart pointer type for
these case, for example:
/// A smart pointer owns the underlying data.
pub struct Owned<T: Ownable> {
ptr: NonNull<T>,
}
impl<T: Ownable> Owned<T> {
/// # Safety
/// `ptr` needs to be a valid pointer, and it should be the
/// unique owner to the object, in other words, no one can touch
/// or free the underlying data.
pub unsafe to_owned(ptr: *mut T) -> Self {
// SAFETY: Per function safety requirement.
Self { ptr: unsafe { NonNull::new_unchecked(ptr) } }
}
/// other safe constructors are available if a initializer (impl
/// Init) is provided
}
/// A Ownable type is a type that can be put into `Owned<T>`, and
/// when `Owned<T>` drops, `ptr_drop` will be called.
pub unsafe trait Ownable {
/// # Safety
/// This could only be called in the `Owned::drop` function.
unsafe fn ptr_drop(ptr: *mut Self);
}
impl<T: Ownable> Drop for Owned<T> {
fn drop(&mut self) {
/// SAFETY: In Owned<T>::drop.
unsafe {
<T as Ownable>::ptr_drop(self.as_mut_ptr());
}
}
}
we can implement Deref and DerefMut easily on `Owned<T>`. And then we
could define Firmware as
#[repr(transparent)]
pub struct Firmware(Opaque<bindings::firmware>);
and
unsafe impl Ownable for Firmware {
unsafe fn ptr_drop(ptr: *mut Self) {
// SAFETY: Per function safety, this is called in
// Owned::drop(), so `ptr` is a unique pointer to object,
// it's safe to release the firmware.
unsafe { bindings::release_firmware(ptr.cast()); }
}
}
and the request_*() will return a `Result<Owned<Self>>`.
Alice mentioned the need of this in page as well:
https://lore.kernel.org/rust-for-linux/CAH5fLgjrt0Ohj1qBv=GrqZumBTMQ1jbsKakChmxmG2JYDJEM8w@mail.gmail.com
Just bring it up while we are (maybe not? ;-)) at it. Also I would like
to hear whether this would work for Firmware in the longer-term ;-) But
yes, I'm not that worried about merging it as it is if others are all
OK.
> +impl Firmware {
> + fn request_internal(name: &CStr, dev: &Device, func: FwFunc) -> Result<Self> {
> + let mut fw: *mut bindings::firmware = core::ptr::null_mut();
> + let pfw: *mut *mut bindings::firmware = &mut fw;
> +
> + // SAFETY: `pfw` is a valid pointer to a NULL initialized `bindings::firmware` pointer.
> + // `name` and `dev` are valid as by their type invariants.
> + let ret = unsafe { func(pfw as _, name.as_char_ptr(), dev.as_raw()) };
> + if ret != 0 {
> + return Err(Error::from_errno(ret));
> + }
> +
> + // SAFETY: `func` not bailing out with a non-zero error code, guarantees that `fw` is a
> + // valid pointer to `bindings::firmware`.
> + Ok(Firmware(unsafe { NonNull::new_unchecked(fw) }))
> + }
> +
> + /// Send a firmware request and wait for it. See also `bindings::request_firmware`.
> + pub fn request(name: &CStr, dev: &Device) -> Result<Self> {
> + Self::request_internal(name, dev, bindings::request_firmware)
> + }
> +
> + /// Send a request for an optional firmware module. See also
> + /// `bindings::firmware_request_nowarn`.
> + pub fn request_nowarn(name: &CStr, dev: &Device) -> Result<Self> {
> + Self::request_internal(name, dev, bindings::firmware_request_nowarn)
> + }
> +
> + fn as_raw(&self) -> *mut bindings::firmware {
> + self.0.as_ptr()
> + }
> +
> + /// Returns the size of the requested firmware in bytes.
> + pub fn size(&self) -> usize {
> + // SAFETY: Safe by the type invariant.
> + unsafe { (*self.as_raw()).size }
> + }
> +
> + /// Returns the requested firmware as `&[u8]`.
> + pub fn data(&self) -> &[u8] {
> + // SAFETY: Safe by the type invariant. Additionally, `bindings::firmware` guarantees, if
Does this "Safe by the type invariant" also covers the following safe
requirement of `from_raw_parts`?
The memory referenced by the returned slice must not be mutated for the duration of lifetime 'a, except inside an UnsafeCell.
in that `&[u8]` has the same lifetime as `&self`, and as long as
`&self` exists, no function can touch the inner `data`? If so, I
probably want to call this out.
Regards,
Boqun
> + // successfully requested, that `bindings::firmware::data` has a size of
> + // `bindings::firmware::size` bytes.
> + unsafe { core::slice::from_raw_parts((*self.as_raw()).data, self.size()) }
> + }
> +}
> +
> +impl Drop for Firmware {
> + fn drop(&mut self) {
> + // SAFETY: Safe by the type invariant.
> + unsafe { bindings::release_firmware(self.as_raw()) };
> + }
> +}
> +
> +// SAFETY: `Firmware` only holds a pointer to a C `struct firmware`, which is safe to be used from
> +// any thread.
> +unsafe impl Send for Firmware {}
> +
> +// SAFETY: `Firmware` only holds a pointer to a C `struct firmware`, references to which are safe to
> +// be used from any thread.
> +unsafe impl Sync for Firmware {}
> diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
> index dd1207f1a873..7707cb013ce9 100644
> --- a/rust/kernel/lib.rs
> +++ b/rust/kernel/lib.rs
> @@ -30,6 +30,8 @@
> mod build_assert;
> pub mod device;
> pub mod error;
> +#[cfg(CONFIG_RUST_FW_LOADER_ABSTRACTIONS)]
> +pub mod firmware;
> pub mod init;
> pub mod ioctl;
> #[cfg(CONFIG_KUNIT)]
> --
> 2.45.1
>
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