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// SPDX-License-Identifier: GPL-2.0-only
//! Abstractions for the faux bus.
//!
//! This module provides bindings for working with faux devices in kernel modules.
//!
//! C header: [`include/linux/device/faux.h`](srctree/include/linux/device/faux.h)
use crate::{
bindings,
device,
prelude::*,
types::Opaque, //
};
use core::{
marker::PhantomData,
ptr::{
null,
null_mut,
NonNull, //
},
};
/// A faux device.
///
/// A faux device is a virtual device backed by the faux bus, primarily used for scenarios where a
/// real hardware device is not available or for testing.
///
/// # Invariants
///
/// The underlying `struct faux_device` is valid.
#[repr(transparent)]
pub struct Device<Ctx: device::DeviceContext = device::Normal>(
Opaque<bindings::faux_device>,
PhantomData<Ctx>,
);
impl<Ctx: device::DeviceContext> Device<Ctx> {
#[inline]
fn as_raw(&self) -> *mut bindings::faux_device {
self.0.get()
}
/// # Safety
///
/// `ptr` must be a valid pointer to a `struct faux_device`.
#[inline]
unsafe fn from_raw<'a>(ptr: *mut bindings::faux_device) -> &'a Self {
// SAFETY: `Device` is a transparent wrapper of `Opaque<bindings::faux_device>`.
unsafe { &*ptr.cast() }
}
}
impl<Ctx: device::DeviceContext> AsRef<device::Device<Ctx>> for Device<Ctx> {
#[inline]
fn as_ref(&self) -> &device::Device<Ctx> {
// SAFETY: By the type invariant of `Self`, `self.as_raw()` is a pointer to a valid
// `struct faux_device`. `dev` points to a valid `struct device`.
unsafe { device::Device::from_raw(&raw mut (*self.as_raw()).dev) }
}
}
// SAFETY: `faux::Device` is a transparent wrapper of `struct faux_device`.
// The offset is guaranteed to point to a valid device field inside `faux::Device`.
unsafe impl<Ctx: device::DeviceContext> device::AsBusDevice<Ctx> for Device<Ctx> {
const OFFSET: usize = core::mem::offset_of!(bindings::faux_device, dev);
}
/// The registration of a faux device.
///
/// This type represents the registration of a [`struct faux_device`]. When an instance of this type
/// is dropped, its respective faux device will be unregistered from the system.
///
/// # Invariants
///
/// - `self.0` always holds a valid pointer to an initialized and registered [`struct faux_device`].
/// - This object is proof that the object described by this `Registration` is bound to a device.
///
/// [`struct faux_device`]: srctree/include/linux/device/faux.h
pub struct Registration(NonNull<bindings::faux_device>);
impl Registration {
/// Create and register a new faux device with the given name.
#[inline]
pub fn new(name: &CStr, parent: Option<&device::Device>) -> Result<Self> {
// SAFETY:
// - `name` is copied by this function into its own storage
// - `faux_ops` is safe to leave NULL according to the C API
// - `parent` can be either NULL or a pointer to a `struct device`, and `faux_device_create`
// will take a reference to `parent` using `device_add` - ensuring that it remains valid
// for the lifetime of the faux device.
let dev = unsafe {
bindings::faux_device_create(
name.as_char_ptr(),
parent.map_or(null_mut(), |p| p.as_raw()),
null(),
)
};
// The above function will return either a valid device, or NULL on failure
// INVARIANT: The device will remain registered until faux_device_destroy() is called, which
// happens in our Drop implementation.
Ok(Self(NonNull::new(dev).ok_or(ENODEV)?))
}
fn as_raw(&self) -> *mut bindings::faux_device {
self.0.as_ptr()
}
}
impl AsRef<Device<device::Bound>> for Registration {
#[inline]
fn as_ref(&self) -> &Device<device::Bound> {
// SAFETY:
// - The underlying `struct faux_device` is guaranteed by the C API to be a valid
// initialized `device`.
// - `faux_match()` always returns 1, and probe runs synchronously
// (PROBE_FORCE_SYNCHRONOUS).
// - `suppress_bind_attrs = true` on faux_driver prevents userspace-triggered unbind via
// sysfs.
// - `mem::forget(Registration)` is not a problem; if the `Registration` is leaked, the faux
// device stays bound forever.
unsafe { Device::from_raw(self.as_raw()) }
}
}
impl Drop for Registration {
#[inline]
fn drop(&mut self) {
// SAFETY: `self.0` is a valid registered faux_device via our type invariants.
unsafe { bindings::faux_device_destroy(self.as_raw()) }
}
}
// SAFETY: The faux device API is thread-safe as guaranteed by the device core, as long as
// faux_device_destroy() is guaranteed to only be called once - which is guaranteed by our type not
// having Copy/Clone.
unsafe impl Send for Registration {}
// SAFETY: The faux device API is thread-safe as guaranteed by the device core, as long as
// faux_device_destroy() is guaranteed to only be called once - which is guaranteed by our type not
// having Copy/Clone.
unsafe impl Sync for Registration {}
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