[PATCH v4 4/5] rust: auxiliary: add auxiliary registration

Danilo Krummrich
2025-04-14T13:19:57Z

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 | 88 +++++++++++++++++++++++++++++++++++++++-
1 file changed, 87 insertions(+), 1 deletion(-)

diff --git a/rust/kernel/auxiliary.rs b/rust/kernel/auxiliary.rs
index 75423737032a..b40d663b42eb 100644
--- a/rust/kernel/auxiliary.rs
+++ b/rust/kernel/auxiliary.rs
@@ -5,7 +5,7 @@
//! C header: [`include/linux/auxiliary_bus.h`](srctree/include/linux/auxiliary_bus.h)

use crate::{
- bindings, device,
+ bindings, container_of, device,
device_id::RawDeviceId,
driver,
error::{to_result, Result},
@@ -230,6 +230,18 @@ pub fn parent(&self) -> Option<&device::Device> {
}
}

+impl Device {
+ 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()) };
+ }
+}
+
// SAFETY: `Device` is a transparent wrapper of a type that doesn't depend on `Device`'s generic
// argument.
kernel::impl_device_context_deref!(unsafe { Device });
@@ -272,3 +284,77 @@ 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 {}
--
2.49.0