[PATCH v3 0/5] Auxiliary bus Rust abstractions

[PATCH v3 0/5] Auxiliary bus Rust abstractions

[Danilo Krummrich]

This series adds Rust abstractions for the auxiliary bus.

It implements the required abstractions to write auxiliary drivers and create
auxiliary device registrations. A driver sample illustrates how the
corresponding abstractions work.

The auxiliary abstractions are required for the Nova driver project, in order to
connect nova-core with the nova-drm driver.

This patch series depends on patches queued for v6.15-rc1 from different trees
(driver-core, nova), plus the patches in [1]; a branch containing the patches,
including the dependencies can be found in [2].

[1] https://lore.kernel.org/lkml/20250319203112.131959-1-dakr@kernel.org/
[2] https://web.git.kernel.org/pub/scm/linux/kernel/git/dakr/linux.git/log/?h=rust/auxiliary

Changes in v3:
  - export auxiliary_bus_type
  - implement impl TryFrom<&Device> for &auxiliary::Device
  - implement Send + Sync for Registration and Device

Changes in v2:
  - implement bus device soundness improvements from [2]

Danilo Krummrich (5):
  rust: types: add `Opaque::zeroed`
  driver: core: auxiliary: export auxiliary_bus_type
  rust: auxiliary: add auxiliary device / driver abstractions
  rust: auxiliary: add auxiliary registration
  samples: rust: add Rust auxiliary driver sample

 MAINTAINERS                           |   2 +
 drivers/base/auxiliary.c              |   3 +-
 include/linux/auxiliary_bus.h         |   2 +
 rust/bindings/bindings_helper.h       |   1 +
 rust/helpers/auxiliary.c              |  23 ++
 rust/helpers/helpers.c                |   1 +
 rust/kernel/auxiliary.rs              | 383 ++++++++++++++++++++++++++
 rust/kernel/lib.rs                    |   2 +
 rust/kernel/types.rs                  |   8 +
 samples/rust/Kconfig                  |  12 +
 samples/rust/Makefile                 |   1 +
 samples/rust/rust_driver_auxiliary.rs | 110 ++++++++
 12 files changed, 547 insertions(+), 1 deletion(-)
 create mode 100644 rust/helpers/auxiliary.c
 create mode 100644 rust/kernel/auxiliary.rs
 create mode 100644 samples/rust/rust_driver_auxiliary.rs

-- 
2.48.1

[PATCH v3 1/5] rust: types: add `Opaque::zeroed`

[Danilo Krummrich]

Analogous to `Opaque::uninit` add `Opaque::zeroed`, which sets the
corresponding memory to zero. In contrast to `Opaque::uninit`, the
corresponding value, depending on its type, may be initialized.

Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Danilo Krummrich <dakr@kernel.org>
---
 rust/kernel/types.rs | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/rust/kernel/types.rs b/rust/kernel/types.rs
index 2bbaab83b9d6..f5e7fed903a7 100644
--- a/rust/kernel/types.rs
+++ b/rust/kernel/types.rs
@@ -326,6 +326,14 @@ pub const fn uninit() -> Self {
         }
     }
 
+    /// Creates a new zeroed opaque value.
+    pub const fn zeroed() -> Self {
+        Self {
+            value: UnsafeCell::new(MaybeUninit::zeroed()),
+            _pin: PhantomPinned,
+        }
+    }
+
     /// Create an opaque pin-initializer from the given pin-initializer.
     pub fn pin_init(slot: impl PinInit<T>) -> impl PinInit<Self> {
         Self::ffi_init(|ptr: *mut T| {
-- 
2.48.1

Re: [PATCH v3 1/5] rust: types: add `Opaque::zeroed`

[Alice Ryhl]

On Wed, Mar 19, 2025 at 09:33:53PM +0100, Danilo Krummrich wrote:
> Analogous to `Opaque::uninit` add `Opaque::zeroed`, which sets the
> corresponding memory to zero. In contrast to `Opaque::uninit`, the
> corresponding value, depending on its type, may be initialized.
> 
> Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Signed-off-by: Danilo Krummrich <dakr@kernel.org>

Reviewed-by: Alice Ryhl <aliceryhl@google.com>

[PATCH v3 2/5] driver: core: auxiliary: export auxiliary_bus_type

[Danilo Krummrich]

In Rust we can safely derive a struct auxiliary_device pointer from a
generic struct device pointer by checking

	dev->bus == auxiliary_bus_type

hence, export auxiliary_bus_type.

Signed-off-by: Danilo Krummrich <dakr@kernel.org>
---
 drivers/base/auxiliary.c      | 3 ++-
 include/linux/auxiliary_bus.h | 2 ++
 2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/base/auxiliary.c b/drivers/base/auxiliary.c
index afa4df4c5a3f..213e26c2747d 100644
--- a/drivers/base/auxiliary.c
+++ b/drivers/base/auxiliary.c
@@ -244,7 +244,7 @@ static void auxiliary_bus_shutdown(struct device *dev)
 		auxdrv->shutdown(auxdev);
 }
 
-static const struct bus_type auxiliary_bus_type = {
+const struct bus_type auxiliary_bus_type = {
 	.name = "auxiliary",
 	.probe = auxiliary_bus_probe,
 	.remove = auxiliary_bus_remove,
@@ -253,6 +253,7 @@ static const struct bus_type auxiliary_bus_type = {
 	.uevent = auxiliary_uevent,
 	.pm = &auxiliary_dev_pm_ops,
 };
+EXPORT_SYMBOL_GPL(auxiliary_bus_type);
 
 /**
  * auxiliary_device_init - check auxiliary_device and initialize
diff --git a/include/linux/auxiliary_bus.h b/include/linux/auxiliary_bus.h
index 65dd7f154374..d4ad9233bfd0 100644
--- a/include/linux/auxiliary_bus.h
+++ b/include/linux/auxiliary_bus.h
@@ -197,6 +197,8 @@ struct auxiliary_driver {
 	const struct auxiliary_device_id *id_table;
 };
 
+extern const struct bus_type auxiliary_bus_type;
+
 static inline void *auxiliary_get_drvdata(struct auxiliary_device *auxdev)
 {
 	return dev_get_drvdata(&auxdev->dev);
-- 
2.48.1

[PATCH v3 3/5] rust: auxiliary: add auxiliary device / driver abstractions

[Danilo Krummrich]

Implement the basic auxiliary abstractions required to implement a
driver matching an auxiliary device.

The design and implementation is analogous to PCI and platform and is
based on the generic device / driver abstractions.

Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Danilo Krummrich <dakr@kernel.org>
---
 MAINTAINERS                     |   1 +
 rust/bindings/bindings_helper.h |   1 +
 rust/helpers/auxiliary.c        |  23 +++
 rust/helpers/helpers.c          |   1 +
 rust/kernel/auxiliary.rs        | 299 ++++++++++++++++++++++++++++++++
 rust/kernel/lib.rs              |   2 +
 6 files changed, 327 insertions(+)
 create mode 100644 rust/helpers/auxiliary.c
 create mode 100644 rust/kernel/auxiliary.rs

diff --git a/MAINTAINERS b/MAINTAINERS
index f5c7022937a7..0a737b28cdfa 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -7114,6 +7114,7 @@ F:	include/linux/kobj*
 F:	include/linux/property.h
 F:	include/linux/sysfs.h
 F:	lib/kobj*
+F:	rust/kernel/auxiliary.rs
 F:	rust/kernel/device.rs
 F:	rust/kernel/device_id.rs
 F:	rust/kernel/devres.rs
diff --git a/rust/bindings/bindings_helper.h b/rust/bindings/bindings_helper.h
index f46cf3bb7069..83026b6e53b2 100644
--- a/rust/bindings/bindings_helper.h
+++ b/rust/bindings/bindings_helper.h
@@ -7,6 +7,7 @@
  */
 
 #include <kunit/test.h>
+#include <linux/auxiliary_bus.h>
 #include <linux/blk-mq.h>
 #include <linux/blk_types.h>
 #include <linux/blkdev.h>
diff --git a/rust/helpers/auxiliary.c b/rust/helpers/auxiliary.c
new file mode 100644
index 000000000000..0db3860d774e
--- /dev/null
+++ b/rust/helpers/auxiliary.c
@@ -0,0 +1,23 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/auxiliary_bus.h>
+
+void rust_helper_auxiliary_set_drvdata(struct auxiliary_device *adev, void *data)
+{
+	auxiliary_set_drvdata(adev, data);
+}
+
+void *rust_helper_auxiliary_get_drvdata(struct auxiliary_device *adev)
+{
+	return auxiliary_get_drvdata(adev);
+}
+
+void rust_helper_auxiliary_device_uninit(struct auxiliary_device *adev)
+{
+	return auxiliary_device_uninit(adev);
+}
+
+void rust_helper_auxiliary_device_delete(struct auxiliary_device *adev)
+{
+	return auxiliary_device_delete(adev);
+}
diff --git a/rust/helpers/helpers.c b/rust/helpers/helpers.c
index 0640b7e115be..d744af85e3b2 100644
--- a/rust/helpers/helpers.c
+++ b/rust/helpers/helpers.c
@@ -7,6 +7,7 @@
  * Sorted alphabetically.
  */
 
+#include "auxiliary.c"
 #include "blk.c"
 #include "bug.c"
 #include "build_assert.c"
diff --git a/rust/kernel/auxiliary.rs b/rust/kernel/auxiliary.rs
new file mode 100644
index 000000000000..1b8015bfca3e
--- /dev/null
+++ b/rust/kernel/auxiliary.rs
@@ -0,0 +1,299 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Abstractions for the auxiliary bus.
+//!
+//! C header: [`include/linux/auxiliary_bus.h`](srctree/include/linux/auxiliary_bus.h)
+
+use crate::{
+    bindings, container_of, device,
+    device_id::RawDeviceId,
+    driver,
+    error::{to_result, Result},
+    prelude::*,
+    str::CStr,
+    types::{ARef, ForeignOwnable, Opaque},
+    ThisModule,
+};
+use core::{
+    convert::TryFrom,
+    marker::PhantomData,
+    ops::Deref,
+    ptr::{addr_of, addr_of_mut, NonNull},
+};
+
+/// An adapter for the registration of auxiliary drivers.
+pub struct Adapter<T: Driver>(T);
+
+// SAFETY: A call to `unregister` for a given instance of `RegType` is guaranteed to be valid if
+// a preceding call to `register` has been successful.
+unsafe impl<T: Driver + 'static> driver::RegistrationOps for Adapter<T> {
+    type RegType = bindings::auxiliary_driver;
+
+    unsafe fn register(
+        adrv: &Opaque<Self::RegType>,
+        name: &'static CStr,
+        module: &'static ThisModule,
+    ) -> Result {
+        // SAFETY: It's safe to set the fields of `struct auxiliary_driver` on initialization.
+        unsafe {
+            (*adrv.get()).name = name.as_char_ptr();
+            (*adrv.get()).probe = Some(Self::probe_callback);
+            (*adrv.get()).remove = Some(Self::remove_callback);
+            (*adrv.get()).id_table = T::ID_TABLE.as_ptr();
+        }
+
+        // SAFETY: `adrv` is guaranteed to be a valid `RegType`.
+        to_result(unsafe {
+            bindings::__auxiliary_driver_register(adrv.get(), module.0, name.as_char_ptr())
+        })
+    }
+
+    unsafe fn unregister(adrv: &Opaque<Self::RegType>) {
+        // SAFETY: `adrv` is guaranteed to be a valid `RegType`.
+        unsafe { bindings::auxiliary_driver_unregister(adrv.get()) }
+    }
+}
+
+impl<T: Driver + 'static> Adapter<T> {
+    extern "C" fn probe_callback(
+        adev: *mut bindings::auxiliary_device,
+        id: *const bindings::auxiliary_device_id,
+    ) -> core::ffi::c_int {
+        // SAFETY: The auxiliary bus only ever calls the probe callback with a valid pointer to a
+        // `struct auxiliary_device`.
+        //
+        // INVARIANT: `adev` is valid for the duration of `probe_callback()`.
+        let adev = unsafe { &*adev.cast::<Device<device::Core>>() };
+
+        // SAFETY: `DeviceId` is a `#[repr(transparent)` wrapper of `struct auxiliary_device_id` and
+        // does not add additional invariants, so it's safe to transmute.
+        let id = unsafe { &*id.cast::<DeviceId>() };
+        let info = T::ID_TABLE.info(id.index());
+
+        match T::probe(adev, info) {
+            Ok(data) => {
+                // Let the `struct auxiliary_device` own a reference of the driver's private data.
+                // SAFETY: By the type invariant `adev.as_raw` returns a valid pointer to a
+                // `struct auxiliary_device`.
+                unsafe { bindings::auxiliary_set_drvdata(adev.as_raw(), data.into_foreign()) };
+            }
+            Err(err) => return Error::to_errno(err),
+        }
+
+        0
+    }
+
+    extern "C" fn remove_callback(adev: *mut bindings::auxiliary_device) {
+        // SAFETY: The auxiliary bus only ever calls the remove callback with a valid pointer to a
+        // `struct auxiliary_device`.
+        let ptr = unsafe { bindings::auxiliary_get_drvdata(adev) };
+
+        // SAFETY: `remove_callback` is only ever called after a successful call to
+        // `probe_callback`, hence it's guaranteed that `ptr` points to a valid and initialized
+        // `KBox<T>` pointer created through `KBox::into_foreign`.
+        let _ = unsafe { KBox::<T>::from_foreign(ptr) };
+    }
+}
+
+/// Declares a kernel module that exposes a single auxiliary driver.
+#[macro_export]
+macro_rules! module_auxiliary_driver {
+    ($($f:tt)*) => {
+        $crate::module_driver!(<T>, $crate::auxiliary::Adapter<T>, { $($f)* });
+    };
+}
+
+/// Abstraction for `bindings::auxiliary_device_id`.
+#[repr(transparent)]
+#[derive(Clone, Copy)]
+pub struct DeviceId(bindings::auxiliary_device_id);
+
+impl DeviceId {
+    /// Create a new [`DeviceId`] from name.
+    pub const fn new(modname: &'static CStr, name: &'static CStr) -> Self {
+        let name = name.as_bytes_with_nul();
+        let modname = modname.as_bytes_with_nul();
+
+        // TODO: Replace with `bindings::auxiliary_device_id::default()` once stabilized for
+        // `const`.
+        //
+        // SAFETY: FFI type is valid to be zero-initialized.
+        let mut id: bindings::auxiliary_device_id = unsafe { core::mem::zeroed() };
+
+        let mut i = 0;
+        while i < modname.len() {
+            id.name[i] = modname[i];
+            i += 1;
+        }
+
+        // Reuse the space of the NULL terminator.
+        id.name[i - 1] = b'.';
+
+        let mut j = 0;
+        while j < name.len() {
+            id.name[i] = name[j];
+            i += 1;
+            j += 1;
+        }
+
+        Self(id)
+    }
+}
+
+// SAFETY:
+// * `DeviceId` is a `#[repr(transparent)` wrapper of `auxiliary_device_id` and does not add
+//   additional invariants, so it's safe to transmute to `RawType`.
+// * `DRIVER_DATA_OFFSET` is the offset to the `driver_data` field.
+unsafe impl RawDeviceId for DeviceId {
+    type RawType = bindings::auxiliary_device_id;
+
+    const DRIVER_DATA_OFFSET: usize =
+        core::mem::offset_of!(bindings::auxiliary_device_id, driver_data);
+
+    fn index(&self) -> usize {
+        self.0.driver_data
+    }
+}
+
+/// IdTable type for auxiliary drivers.
+pub type IdTable<T> = &'static dyn kernel::device_id::IdTable<DeviceId, T>;
+
+/// Create a auxiliary `IdTable` with its alias for modpost.
+#[macro_export]
+macro_rules! auxiliary_device_table {
+    ($table_name:ident, $module_table_name:ident, $id_info_type: ty, $table_data: expr) => {
+        const $table_name: $crate::device_id::IdArray<
+            $crate::auxiliary::DeviceId,
+            $id_info_type,
+            { $table_data.len() },
+        > = $crate::device_id::IdArray::new($table_data);
+
+        $crate::module_device_table!("auxiliary", $module_table_name, $table_name);
+    };
+}
+
+/// The auxiliary driver trait.
+///
+/// Drivers must implement this trait in order to get an auxiliary driver registered.
+pub trait Driver {
+    /// The type holding information about each device id supported by the driver.
+    ///
+    /// TODO: Use associated_type_defaults once stabilized:
+    ///
+    /// type IdInfo: 'static = ();
+    type IdInfo: 'static;
+
+    /// The table of device ids supported by the driver.
+    const ID_TABLE: IdTable<Self::IdInfo>;
+
+    /// Auxiliary driver probe.
+    ///
+    /// Called when a new auxiliary device is added or discovered. Implementers should attempt
+    /// to initialize the device here.
+    fn probe(dev: &Device<device::Core>, id_info: &Self::IdInfo) -> Result<Pin<KBox<Self>>>;
+}
+
+/// The auxiliary device representation.
+///
+/// This structure represents the Rust abstraction for a C `struct auxiliary_device`. The
+/// implementation abstracts the usage of an already existing C `struct auxiliary_device` within
+/// Rust code that we get passed from the C side.
+///
+/// # Invariants
+///
+/// A [`Device`] instance represents a valid `struct auxiliary_device` created by the C portion of
+/// the kernel.
+#[repr(transparent)]
+pub struct Device<Ctx: device::DeviceContext = device::Normal>(
+    Opaque<bindings::auxiliary_device>,
+    PhantomData<Ctx>,
+);
+
+impl Device {
+    fn as_raw(&self) -> *mut bindings::auxiliary_device {
+        self.0.get()
+    }
+
+    /// Returns the auxiliary device' id.
+    pub fn id(&self) -> u32 {
+        // SAFETY: By the type invariant `self.as_raw()` is a valid pointer to a
+        // `struct auxiliary_device`.
+        unsafe { (*self.as_raw()).id }
+    }
+}
+
+impl Deref for Device<device::Core> {
+    type Target = Device;
+
+    fn deref(&self) -> &Self::Target {
+        let ptr: *const Self = self;
+
+        // CAST: `Device<Ctx>` is a transparent wrapper of `Opaque<bindings::auxiliary_device>`.
+        let ptr = ptr.cast::<Device>();
+
+        // SAFETY: `ptr` was derived from `&self`.
+        unsafe { &*ptr }
+    }
+}
+
+impl From<&Device<device::Core>> for ARef<Device> {
+    fn from(dev: &Device<device::Core>) -> Self {
+        (&**dev).into()
+    }
+}
+
+// SAFETY: Instances of `Device` are always reference-counted.
+unsafe impl crate::types::AlwaysRefCounted for Device {
+    fn inc_ref(&self) {
+        // SAFETY: The existence of a shared reference guarantees that the refcount is non-zero.
+        unsafe { bindings::get_device(self.as_ref().as_raw()) };
+    }
+
+    unsafe fn dec_ref(obj: NonNull<Self>) {
+        // CAST: `Self` a transparent wrapper of `bindings::auxiliary_device`.
+        let adev: *mut bindings::auxiliary_device = obj.cast().as_ptr();
+
+        // SAFETY: By the type invariant of `Self`, `adev` is a pointer to a valid
+        // `struct auxiliary_device`.
+        let dev = unsafe { addr_of_mut!((*adev).dev) };
+
+        // SAFETY: The safety requirements guarantee that the refcount is non-zero.
+        unsafe { bindings::put_device(dev) }
+    }
+}
+
+impl AsRef<device::Device> for Device {
+    fn as_ref(&self) -> &device::Device {
+        // SAFETY: By the type invariant of `Self`, `self.as_raw()` is a pointer to a valid
+        // `struct auxiliary_device`.
+        let dev = unsafe { addr_of_mut!((*self.as_raw()).dev) };
+
+        // SAFETY: `dev` points to a valid `struct device`.
+        unsafe { device::Device::as_ref(dev) }
+    }
+}
+
+impl TryFrom<&device::Device> for &Device {
+    type Error = kernel::error::Error;
+
+    fn try_from(dev: &device::Device) -> Result<Self, Self::Error> {
+        if dev.bus_type_raw() != addr_of!(bindings::auxiliary_bus_type) {
+            return Err(EINVAL);
+        }
+
+        // SAFETY: We've just verified that the bus type of `dev` equals
+        // `bindings::auxiliary_bus_type`, hence `dev` must be embedded in a valid
+        // `struct auxiliary_device`.
+        let adev = unsafe { container_of!(dev.as_raw(), bindings::auxiliary_device, dev) };
+
+        // SAFETY: `adev` is a valid pointer to a `struct auxiliary_device`.
+        Ok(unsafe { &*adev.cast() })
+    }
+}
+
+// SAFETY: A `Device` is always reference-counted and can be released from any thread.
+unsafe impl Send for Device {}
+
+// SAFETY: `Device` can be shared among threads because all methods of `Device`
+// (i.e. `Device<Normal>) are thread safe.
+unsafe impl Sync for Device {}
diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
index 398242f92a96..d9a2ca9d1f20 100644
--- a/rust/kernel/lib.rs
+++ b/rust/kernel/lib.rs
@@ -36,6 +36,8 @@
 pub use ffi;
 
 pub mod alloc;
+#[cfg(CONFIG_AUXILIARY_BUS)]
+pub mod auxiliary;
 #[cfg(CONFIG_BLOCK)]
 pub mod block;
 #[doc(hidden)]
-- 
2.48.1

[PATCH v3 4/5] rust: auxiliary: add auxiliary registration

[Danilo Krummrich]

Implement the `auxiliary::Registration` type, which provides an API to
create and register new auxiliary devices in the system.

Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Danilo Krummrich <dakr@kernel.org>
---
 rust/kernel/auxiliary.rs | 84 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 84 insertions(+)

diff --git a/rust/kernel/auxiliary.rs b/rust/kernel/auxiliary.rs
index 1b8015bfca3e..ff69fde760d8 100644
--- a/rust/kernel/auxiliary.rs
+++ b/rust/kernel/auxiliary.rs
@@ -220,6 +220,16 @@ pub fn id(&self) -> u32 {
         // `struct auxiliary_device`.
         unsafe { (*self.as_raw()).id }
     }
+
+    extern "C" fn release(dev: *mut bindings::device) {
+        // SAFETY: By the type invariant `self.0.as_raw` is a pointer to the `struct device`
+        // embedded in `struct auxiliary_device`.
+        let adev = unsafe { container_of!(dev, bindings::auxiliary_device, dev) }.cast_mut();
+
+        // SAFETY: `adev` points to the memory that has been allocated in `Registration::new`, via
+        // `KBox::new(Opaque::<bindings::auxiliary_device>::zeroed(), GFP_KERNEL)`.
+        let _ = unsafe { KBox::<Opaque<bindings::auxiliary_device>>::from_raw(adev.cast()) };
+    }
 }
 
 impl Deref for Device<device::Core> {
@@ -297,3 +307,77 @@ unsafe impl Send for Device {}
 // SAFETY: `Device` can be shared among threads because all methods of `Device`
 // (i.e. `Device<Normal>) are thread safe.
 unsafe impl Sync for Device {}
+
+/// The registration of an auxiliary device.
+///
+/// This type represents the registration of a [`struct auxiliary_device`]. When an instance of this
+/// type is dropped, its respective auxiliary device will be unregistered from the system.
+///
+/// # Invariants
+///
+/// `self.0` always holds a valid pointer to an initialized and registered
+/// [`struct auxiliary_device`].
+pub struct Registration(NonNull<bindings::auxiliary_device>);
+
+impl Registration {
+    /// Create and register a new auxiliary device.
+    pub fn new(parent: &device::Device, name: &CStr, id: u32, modname: &CStr) -> Result<Self> {
+        let boxed = KBox::new(Opaque::<bindings::auxiliary_device>::zeroed(), GFP_KERNEL)?;
+        let adev = boxed.get();
+
+        // SAFETY: It's safe to set the fields of `struct auxiliary_device` on initialization.
+        unsafe {
+            (*adev).dev.parent = parent.as_raw();
+            (*adev).dev.release = Some(Device::release);
+            (*adev).name = name.as_char_ptr();
+            (*adev).id = id;
+        }
+
+        // SAFETY: `adev` is guaranteed to be a valid pointer to a `struct auxiliary_device`,
+        // which has not been initialized yet.
+        unsafe { bindings::auxiliary_device_init(adev) };
+
+        // Now that `adev` is initialized, leak the `Box`; the corresponding memory will be freed
+        // by `Device::release` when the last reference to the `struct auxiliary_device` is dropped.
+        let _ = KBox::into_raw(boxed);
+
+        // SAFETY:
+        // - `adev` is guaranteed to be a valid pointer to a `struct auxiliary_device`, which has
+        //   been initialialized,
+        // - `modname.as_char_ptr()` is a NULL terminated string.
+        let ret = unsafe { bindings::__auxiliary_device_add(adev, modname.as_char_ptr()) };
+        if ret != 0 {
+            // SAFETY: `adev` is guaranteed to be a valid pointer to a `struct auxiliary_device`,
+            // which has been initialialized.
+            unsafe { bindings::auxiliary_device_uninit(adev) };
+
+            return Err(Error::from_errno(ret));
+        }
+
+        // SAFETY: `adev` is guaranteed to be non-null, since the `KBox` was allocated successfully.
+        //
+        // INVARIANT: The device will remain registered until `auxiliary_device_delete()` is called,
+        // which happens in `Self::drop()`.
+        Ok(Self(unsafe { NonNull::new_unchecked(adev) }))
+    }
+}
+
+impl Drop for Registration {
+    fn drop(&mut self) {
+        // SAFETY: By the type invariant of `Self`, `self.0.as_ptr()` is a valid registered
+        // `struct auxiliary_device`.
+        unsafe { bindings::auxiliary_device_delete(self.0.as_ptr()) };
+
+        // This drops the reference we acquired through `auxiliary_device_init()`.
+        //
+        // SAFETY: By the type invariant of `Self`, `self.0.as_ptr()` is a valid registered
+        // `struct auxiliary_device`.
+        unsafe { bindings::auxiliary_device_uninit(self.0.as_ptr()) };
+    }
+}
+
+// SAFETY: A `Registration` of a `struct auxiliary_device` can be released from any thread.
+unsafe impl Send for Registration {}
+
+// SAFETY: `Registration` does not expose any methods or fields that need synchronization.
+unsafe impl Sync for Registration {}
-- 
2.48.1

[PATCH v3 5/5] samples: rust: add Rust auxiliary driver sample

[Danilo Krummrich]

Add a sample Rust auxiliary driver based on a PCI driver for QEMU's
"pci-testdev" device.

The PCI driver only registers an auxiliary device, in order to make the
corresponding auxiliary driver probe.

Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Danilo Krummrich <dakr@kernel.org>
---
 MAINTAINERS                           |   1 +
 samples/rust/Kconfig                  |  12 +++
 samples/rust/Makefile                 |   1 +
 samples/rust/rust_driver_auxiliary.rs | 110 ++++++++++++++++++++++++++
 4 files changed, 124 insertions(+)
 create mode 100644 samples/rust/rust_driver_auxiliary.rs

diff --git a/MAINTAINERS b/MAINTAINERS
index 0a737b28cdfa..6ec20e4f715d 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -7121,6 +7121,7 @@ F:	rust/kernel/devres.rs
 F:	rust/kernel/driver.rs
 F:	rust/kernel/faux.rs
 F:	rust/kernel/platform.rs
+F:	samples/rust/rust_driver_auxiliary.rs
 F:	samples/rust/rust_driver_platform.rs
 F:	samples/rust/rust_driver_faux.rs
 
diff --git a/samples/rust/Kconfig b/samples/rust/Kconfig
index 3b6eae84b297..413216da1b70 100644
--- a/samples/rust/Kconfig
+++ b/samples/rust/Kconfig
@@ -71,6 +71,18 @@ config SAMPLE_RUST_DRIVER_FAUX
 
 	  If unsure, say N.
 
+config SAMPLE_RUST_DRIVER_AUXILIARY
+	tristate "Auxiliary Driver"
+	depends on AUXILIARY_BUS
+	depends on PCI
+	help
+	  This option builds the Rust auxiliary driver sample.
+
+	  To compile this as a module, choose M here:
+	  the module will be called rust_driver_auxiliary.
+
+	  If unsure, say N.
+
 config SAMPLE_RUST_HOSTPROGS
 	bool "Host programs"
 	help
diff --git a/samples/rust/Makefile b/samples/rust/Makefile
index 0dbc6d90f1ef..30a8809d0a15 100644
--- a/samples/rust/Makefile
+++ b/samples/rust/Makefile
@@ -7,6 +7,7 @@ obj-$(CONFIG_SAMPLE_RUST_PRINT)			+= rust_print.o
 obj-$(CONFIG_SAMPLE_RUST_DRIVER_PCI)		+= rust_driver_pci.o
 obj-$(CONFIG_SAMPLE_RUST_DRIVER_PLATFORM)	+= rust_driver_platform.o
 obj-$(CONFIG_SAMPLE_RUST_DRIVER_FAUX)		+= rust_driver_faux.o
+obj-$(CONFIG_SAMPLE_RUST_DRIVER_AUXILIARY)	+= rust_driver_auxiliary.o
 
 rust_print-y := rust_print_main.o rust_print_events.o
 
diff --git a/samples/rust/rust_driver_auxiliary.rs b/samples/rust/rust_driver_auxiliary.rs
new file mode 100644
index 000000000000..0f03d1d2181e
--- /dev/null
+++ b/samples/rust/rust_driver_auxiliary.rs
@@ -0,0 +1,110 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Rust auxiliary driver sample (based on a PCI driver for QEMU's `pci-testdev`).
+//!
+//! To make this driver probe, QEMU must be run with `-device pci-testdev`.
+
+use kernel::{
+    auxiliary, bindings, c_str, device::Core, driver, error::Error, init, pci, prelude::*,
+    str::CStr, InPlaceModule,
+};
+
+const MODULE_NAME: &CStr = <LocalModule as kernel::ModuleMetadata>::NAME;
+const AUXILIARY_NAME: &CStr = c_str!("auxiliary");
+
+struct AuxiliaryDriver;
+
+kernel::auxiliary_device_table!(
+    AUX_TABLE,
+    MODULE_AUX_TABLE,
+    <AuxiliaryDriver as auxiliary::Driver>::IdInfo,
+    [(auxiliary::DeviceId::new(MODULE_NAME, AUXILIARY_NAME), ())]
+);
+
+impl auxiliary::Driver for AuxiliaryDriver {
+    type IdInfo = ();
+
+    const ID_TABLE: auxiliary::IdTable<Self::IdInfo> = &AUX_TABLE;
+
+    fn probe(adev: &auxiliary::Device<Core>, _info: &Self::IdInfo) -> Result<Pin<KBox<Self>>> {
+        dev_info!(
+            adev.as_ref(),
+            "Probing auxiliary driver for auxiliary device with id={}\n",
+            adev.id()
+        );
+
+        if let Some(parent) = adev.as_ref().parent() {
+            let pdev: &pci::Device = parent.try_into()?;
+
+            dev_info!(
+                adev.as_ref(),
+                "Parent: VendorID={:#x}, DeviceID={:#x}\n",
+                pdev.vendor_id(),
+                pdev.device_id()
+            );
+        }
+
+        let this = KBox::new(Self, GFP_KERNEL)?;
+
+        Ok(this.into())
+    }
+}
+
+struct PciDriver {
+    _reg: [auxiliary::Registration; 2],
+}
+
+kernel::pci_device_table!(
+    PCI_TABLE,
+    MODULE_PCI_TABLE,
+    <PciDriver as pci::Driver>::IdInfo,
+    [(
+        pci::DeviceId::from_id(bindings::PCI_VENDOR_ID_REDHAT, 0x5),
+        ()
+    )]
+);
+
+impl pci::Driver for PciDriver {
+    type IdInfo = ();
+
+    const ID_TABLE: pci::IdTable<Self::IdInfo> = &PCI_TABLE;
+
+    fn probe(pdev: &pci::Device<Core>, _info: &Self::IdInfo) -> Result<Pin<KBox<Self>>> {
+        let this = KBox::new(
+            Self {
+                _reg: [
+                    auxiliary::Registration::new(pdev.as_ref(), AUXILIARY_NAME, 0, MODULE_NAME)?,
+                    auxiliary::Registration::new(pdev.as_ref(), AUXILIARY_NAME, 1, MODULE_NAME)?,
+                ],
+            },
+            GFP_KERNEL,
+        )?;
+
+        Ok(this.into())
+    }
+}
+
+#[pin_data]
+struct SampleModule {
+    #[pin]
+    _pci_driver: driver::Registration<pci::Adapter<PciDriver>>,
+    #[pin]
+    _aux_driver: driver::Registration<auxiliary::Adapter<AuxiliaryDriver>>,
+}
+
+impl InPlaceModule for SampleModule {
+    fn init(module: &'static kernel::ThisModule) -> impl init::PinInit<Self, Error> {
+        try_pin_init!(Self {
+            _pci_driver <- driver::Registration::new(MODULE_NAME, module),
+            _aux_driver <- driver::Registration::new(MODULE_NAME, module),
+        })
+    }
+}
+
+module! {
+    type: SampleModule,
+    name: "rust_driver_auxiliary",
+    author: "Danilo Krummrich",
+    description: "Rust auxiliary driver",
+    license: "GPL v2",
+}
-- 
2.48.1