kernel/
faux.rs

1// SPDX-License-Identifier: GPL-2.0-only
2
3//! Abstractions for the faux bus.
4//!
5//! This module provides bindings for working with faux devices in kernel modules.
6//!
7//! C header: [`include/linux/device/faux.h`](srctree/include/linux/device/faux.h)
8
9use crate::{
10    bindings,
11    device,
12    prelude::*,
13    types::Opaque, //
14};
15use core::{
16    marker::PhantomData,
17    ptr::{
18        null,
19        null_mut,
20        NonNull, //
21    },
22};
23
24/// A faux device.
25///
26/// A faux device is a virtual device backed by the faux bus, primarily used for scenarios where a
27/// real hardware device is not available or for testing.
28///
29/// # Invariants
30///
31/// The underlying `struct faux_device` is valid.
32#[repr(transparent)]
33pub struct Device<Ctx: device::DeviceContext = device::Normal>(
34    Opaque<bindings::faux_device>,
35    PhantomData<Ctx>,
36);
37
38impl<Ctx: device::DeviceContext> Device<Ctx> {
39    #[inline]
40    fn as_raw(&self) -> *mut bindings::faux_device {
41        self.0.get()
42    }
43
44    /// # Safety
45    ///
46    /// `ptr` must be a valid pointer to a `struct faux_device`.
47    #[inline]
48    unsafe fn from_raw<'a>(ptr: *mut bindings::faux_device) -> &'a Self {
49        // SAFETY: `Device` is a transparent wrapper of `Opaque<bindings::faux_device>`.
50        unsafe { &*ptr.cast() }
51    }
52}
53
54impl<Ctx: device::DeviceContext> AsRef<device::Device<Ctx>> for Device<Ctx> {
55    #[inline]
56    fn as_ref(&self) -> &device::Device<Ctx> {
57        // SAFETY: By the type invariant of `Self`, `self.as_raw()` is a pointer to a valid
58        // `struct faux_device`. `dev` points to a valid `struct device`.
59        unsafe { device::Device::from_raw(&raw mut (*self.as_raw()).dev) }
60    }
61}
62
63// SAFETY: `faux::Device` is a transparent wrapper of `struct faux_device`.
64// The offset is guaranteed to point to a valid device field inside `faux::Device`.
65unsafe impl<Ctx: device::DeviceContext> device::AsBusDevice<Ctx> for Device<Ctx> {
66    const OFFSET: usize = core::mem::offset_of!(bindings::faux_device, dev);
67}
68
69/// The registration of a faux device.
70///
71/// This type represents the registration of a [`struct faux_device`]. When an instance of this type
72/// is dropped, its respective faux device will be unregistered from the system.
73///
74/// # Invariants
75///
76/// - `self.0` always holds a valid pointer to an initialized and registered [`struct faux_device`].
77/// - This object is proof that the object described by this `Registration` is bound to a device.
78///
79/// [`struct faux_device`]: srctree/include/linux/device/faux.h
80pub struct Registration(NonNull<bindings::faux_device>);
81
82impl Registration {
83    /// Create and register a new faux device with the given name.
84    #[inline]
85    pub fn new(name: &CStr, parent: Option<&device::Device>) -> Result<Self> {
86        // SAFETY:
87        // - `name` is copied by this function into its own storage
88        // - `faux_ops` is safe to leave NULL according to the C API
89        // - `parent` can be either NULL or a pointer to a `struct device`, and `faux_device_create`
90        //   will take a reference to `parent` using `device_add` - ensuring that it remains valid
91        //   for the lifetime of the faux device.
92        let dev = unsafe {
93            bindings::faux_device_create(
94                name.as_char_ptr(),
95                parent.map_or(null_mut(), |p| p.as_raw()),
96                null(),
97            )
98        };
99
100        // The above function will return either a valid device, or NULL on failure
101        // INVARIANT: The device will remain registered until faux_device_destroy() is called, which
102        // happens in our Drop implementation.
103        Ok(Self(NonNull::new(dev).ok_or(ENODEV)?))
104    }
105
106    fn as_raw(&self) -> *mut bindings::faux_device {
107        self.0.as_ptr()
108    }
109}
110
111impl AsRef<Device<device::Bound>> for Registration {
112    #[inline]
113    fn as_ref(&self) -> &Device<device::Bound> {
114        // SAFETY:
115        // - The underlying `struct faux_device` is guaranteed by the C API to be a valid
116        //   initialized `device`.
117        // - `faux_match()` always returns 1, and probe runs synchronously
118        //   (PROBE_FORCE_SYNCHRONOUS).
119        // - `suppress_bind_attrs = true` on faux_driver prevents userspace-triggered unbind via
120        //   sysfs.
121        // - `mem::forget(Registration)` is not a problem; if the `Registration` is leaked, the faux
122        //   device stays bound forever.
123        unsafe { Device::from_raw(self.as_raw()) }
124    }
125}
126
127impl Drop for Registration {
128    #[inline]
129    fn drop(&mut self) {
130        // SAFETY: `self.0` is a valid registered faux_device via our type invariants.
131        unsafe { bindings::faux_device_destroy(self.as_raw()) }
132    }
133}
134
135// SAFETY: The faux device API is thread-safe as guaranteed by the device core, as long as
136// faux_device_destroy() is guaranteed to only be called once - which is guaranteed by our type not
137// having Copy/Clone.
138unsafe impl Send for Registration {}
139
140// SAFETY: The faux device API is thread-safe as guaranteed by the device core, as long as
141// faux_device_destroy() is guaranteed to only be called once - which is guaranteed by our type not
142// having Copy/Clone.
143unsafe impl Sync for Registration {}
kernel/faux.rs

kernel/
faux.rs
