kernel/miscdevice.rs
1// SPDX-License-Identifier: GPL-2.0
2
3// Copyright (C) 2024 Google LLC.
4
5//! Miscdevice support.
6//!
7//! C headers: [`include/linux/miscdevice.h`](srctree/include/linux/miscdevice.h).
8//!
9//! Reference: <https://www.kernel.org/doc/html/latest/driver-api/misc_devices.html>
10
11use crate::{
12 bindings,
13 device::Device,
14 error::{to_result, Error, Result, VTABLE_DEFAULT_ERROR},
15 ffi::{c_int, c_long, c_uint, c_ulong},
16 fs::File,
17 mm::virt::VmaNew,
18 prelude::*,
19 seq_file::SeqFile,
20 str::CStr,
21 types::{ForeignOwnable, Opaque},
22};
23use core::{marker::PhantomData, mem::MaybeUninit, pin::Pin};
24
25/// Options for creating a misc device.
26#[derive(Copy, Clone)]
27pub struct MiscDeviceOptions {
28 /// The name of the miscdevice.
29 pub name: &'static CStr,
30}
31
32impl MiscDeviceOptions {
33 /// Create a raw `struct miscdev` ready for registration.
34 pub const fn into_raw<T: MiscDevice>(self) -> bindings::miscdevice {
35 // SAFETY: All zeros is valid for this C type.
36 let mut result: bindings::miscdevice = unsafe { MaybeUninit::zeroed().assume_init() };
37 result.minor = bindings::MISC_DYNAMIC_MINOR as ffi::c_int;
38 result.name = self.name.as_char_ptr();
39 result.fops = MiscdeviceVTable::<T>::build();
40 result
41 }
42}
43
44/// A registration of a miscdevice.
45///
46/// # Invariants
47///
48/// - `inner` contains a `struct miscdevice` that is registered using
49/// `misc_register()`.
50/// - This registration remains valid for the entire lifetime of the
51/// [`MiscDeviceRegistration`] instance.
52/// - Deregistration occurs exactly once in [`Drop`] via `misc_deregister()`.
53/// - `inner` wraps a valid, pinned `miscdevice` created using
54/// [`MiscDeviceOptions::into_raw`].
55#[repr(transparent)]
56#[pin_data(PinnedDrop)]
57pub struct MiscDeviceRegistration<T> {
58 #[pin]
59 inner: Opaque<bindings::miscdevice>,
60 _t: PhantomData<T>,
61}
62
63// SAFETY: It is allowed to call `misc_deregister` on a different thread from where you called
64// `misc_register`.
65unsafe impl<T> Send for MiscDeviceRegistration<T> {}
66// SAFETY: All `&self` methods on this type are written to ensure that it is safe to call them in
67// parallel.
68unsafe impl<T> Sync for MiscDeviceRegistration<T> {}
69
70impl<T: MiscDevice> MiscDeviceRegistration<T> {
71 /// Register a misc device.
72 pub fn register(opts: MiscDeviceOptions) -> impl PinInit<Self, Error> {
73 try_pin_init!(Self {
74 inner <- Opaque::try_ffi_init(move |slot: *mut bindings::miscdevice| {
75 // SAFETY: The initializer can write to the provided `slot`.
76 unsafe { slot.write(opts.into_raw::<T>()) };
77
78 // SAFETY: We just wrote the misc device options to the slot. The miscdevice will
79 // get unregistered before `slot` is deallocated because the memory is pinned and
80 // the destructor of this type deallocates the memory.
81 // INVARIANT: If this returns `Ok(())`, then the `slot` will contain a registered
82 // misc device.
83 to_result(unsafe { bindings::misc_register(slot) })
84 }),
85 _t: PhantomData,
86 })
87 }
88
89 /// Returns a raw pointer to the misc device.
90 pub fn as_raw(&self) -> *mut bindings::miscdevice {
91 self.inner.get()
92 }
93
94 /// Access the `this_device` field.
95 pub fn device(&self) -> &Device {
96 // SAFETY: This can only be called after a successful register(), which always
97 // initialises `this_device` with a valid device. Furthermore, the signature of this
98 // function tells the borrow-checker that the `&Device` reference must not outlive the
99 // `&MiscDeviceRegistration<T>` used to obtain it, so the last use of the reference must be
100 // before the underlying `struct miscdevice` is destroyed.
101 unsafe { Device::as_ref((*self.as_raw()).this_device) }
102 }
103}
104
105#[pinned_drop]
106impl<T> PinnedDrop for MiscDeviceRegistration<T> {
107 fn drop(self: Pin<&mut Self>) {
108 // SAFETY: We know that the device is registered by the type invariants.
109 unsafe { bindings::misc_deregister(self.inner.get()) };
110 }
111}
112
113/// Trait implemented by the private data of an open misc device.
114#[vtable]
115pub trait MiscDevice: Sized {
116 /// What kind of pointer should `Self` be wrapped in.
117 type Ptr: ForeignOwnable + Send + Sync;
118
119 /// Called when the misc device is opened.
120 ///
121 /// The returned pointer will be stored as the private data for the file.
122 fn open(_file: &File, _misc: &MiscDeviceRegistration<Self>) -> Result<Self::Ptr>;
123
124 /// Called when the misc device is released.
125 fn release(device: Self::Ptr, _file: &File) {
126 drop(device);
127 }
128
129 /// Handle for mmap.
130 ///
131 /// This function is invoked when a user space process invokes the `mmap` system call on
132 /// `file`. The function is a callback that is part of the VMA initializer. The kernel will do
133 /// initial setup of the VMA before calling this function. The function can then interact with
134 /// the VMA initialization by calling methods of `vma`. If the function does not return an
135 /// error, the kernel will complete initialization of the VMA according to the properties of
136 /// `vma`.
137 fn mmap(
138 _device: <Self::Ptr as ForeignOwnable>::Borrowed<'_>,
139 _file: &File,
140 _vma: &VmaNew,
141 ) -> Result {
142 build_error!(VTABLE_DEFAULT_ERROR)
143 }
144
145 /// Handler for ioctls.
146 ///
147 /// The `cmd` argument is usually manipulated using the utilities in [`kernel::ioctl`].
148 ///
149 /// [`kernel::ioctl`]: mod@crate::ioctl
150 fn ioctl(
151 _device: <Self::Ptr as ForeignOwnable>::Borrowed<'_>,
152 _file: &File,
153 _cmd: u32,
154 _arg: usize,
155 ) -> Result<isize> {
156 build_error!(VTABLE_DEFAULT_ERROR)
157 }
158
159 /// Handler for ioctls.
160 ///
161 /// Used for 32-bit userspace on 64-bit platforms.
162 ///
163 /// This method is optional and only needs to be provided if the ioctl relies on structures
164 /// that have different layout on 32-bit and 64-bit userspace. If no implementation is
165 /// provided, then `compat_ptr_ioctl` will be used instead.
166 #[cfg(CONFIG_COMPAT)]
167 fn compat_ioctl(
168 _device: <Self::Ptr as ForeignOwnable>::Borrowed<'_>,
169 _file: &File,
170 _cmd: u32,
171 _arg: usize,
172 ) -> Result<isize> {
173 build_error!(VTABLE_DEFAULT_ERROR)
174 }
175
176 /// Show info for this fd.
177 fn show_fdinfo(
178 _device: <Self::Ptr as ForeignOwnable>::Borrowed<'_>,
179 _m: &SeqFile,
180 _file: &File,
181 ) {
182 build_error!(VTABLE_DEFAULT_ERROR)
183 }
184}
185
186/// A vtable for the file operations of a Rust miscdevice.
187struct MiscdeviceVTable<T: MiscDevice>(PhantomData<T>);
188
189impl<T: MiscDevice> MiscdeviceVTable<T> {
190 /// # Safety
191 ///
192 /// `file` and `inode` must be the file and inode for a file that is undergoing initialization.
193 /// The file must be associated with a `MiscDeviceRegistration<T>`.
194 unsafe extern "C" fn open(inode: *mut bindings::inode, raw_file: *mut bindings::file) -> c_int {
195 // SAFETY: The pointers are valid and for a file being opened.
196 let ret = unsafe { bindings::generic_file_open(inode, raw_file) };
197 if ret != 0 {
198 return ret;
199 }
200
201 // SAFETY: The open call of a file can access the private data.
202 let misc_ptr = unsafe { (*raw_file).private_data };
203
204 // SAFETY: This is a miscdevice, so `misc_open()` set the private data to a pointer to the
205 // associated `struct miscdevice` before calling into this method. Furthermore,
206 // `misc_open()` ensures that the miscdevice can't be unregistered and freed during this
207 // call to `fops_open`.
208 let misc = unsafe { &*misc_ptr.cast::<MiscDeviceRegistration<T>>() };
209
210 // SAFETY:
211 // * This underlying file is valid for (much longer than) the duration of `T::open`.
212 // * There is no active fdget_pos region on the file on this thread.
213 let file = unsafe { File::from_raw_file(raw_file) };
214
215 let ptr = match T::open(file, misc) {
216 Ok(ptr) => ptr,
217 Err(err) => return err.to_errno(),
218 };
219
220 // This overwrites the private data with the value specified by the user, changing the type
221 // of this file's private data. All future accesses to the private data is performed by
222 // other fops_* methods in this file, which all correctly cast the private data to the new
223 // type.
224 //
225 // SAFETY: The open call of a file can access the private data.
226 unsafe { (*raw_file).private_data = ptr.into_foreign().cast() };
227
228 0
229 }
230
231 /// # Safety
232 ///
233 /// `file` and `inode` must be the file and inode for a file that is being released. The file
234 /// must be associated with a `MiscDeviceRegistration<T>`.
235 unsafe extern "C" fn release(_inode: *mut bindings::inode, file: *mut bindings::file) -> c_int {
236 // SAFETY: The release call of a file owns the private data.
237 let private = unsafe { (*file).private_data }.cast();
238 // SAFETY: The release call of a file owns the private data.
239 let ptr = unsafe { <T::Ptr as ForeignOwnable>::from_foreign(private) };
240
241 // SAFETY:
242 // * The file is valid for the duration of this call.
243 // * There is no active fdget_pos region on the file on this thread.
244 T::release(ptr, unsafe { File::from_raw_file(file) });
245
246 0
247 }
248
249 /// # Safety
250 ///
251 /// `file` must be a valid file that is associated with a `MiscDeviceRegistration<T>`.
252 /// `vma` must be a vma that is currently being mmap'ed with this file.
253 unsafe extern "C" fn mmap(
254 file: *mut bindings::file,
255 vma: *mut bindings::vm_area_struct,
256 ) -> c_int {
257 // SAFETY: The mmap call of a file can access the private data.
258 let private = unsafe { (*file).private_data };
259 // SAFETY: This is a Rust Miscdevice, so we call `into_foreign` in `open` and
260 // `from_foreign` in `release`, and `fops_mmap` is guaranteed to be called between those
261 // two operations.
262 let device = unsafe { <T::Ptr as ForeignOwnable>::borrow(private.cast()) };
263 // SAFETY: The caller provides a vma that is undergoing initial VMA setup.
264 let area = unsafe { VmaNew::from_raw(vma) };
265 // SAFETY:
266 // * The file is valid for the duration of this call.
267 // * There is no active fdget_pos region on the file on this thread.
268 let file = unsafe { File::from_raw_file(file) };
269
270 match T::mmap(device, file, area) {
271 Ok(()) => 0,
272 Err(err) => err.to_errno(),
273 }
274 }
275
276 /// # Safety
277 ///
278 /// `file` must be a valid file that is associated with a `MiscDeviceRegistration<T>`.
279 unsafe extern "C" fn ioctl(file: *mut bindings::file, cmd: c_uint, arg: c_ulong) -> c_long {
280 // SAFETY: The ioctl call of a file can access the private data.
281 let private = unsafe { (*file).private_data }.cast();
282 // SAFETY: Ioctl calls can borrow the private data of the file.
283 let device = unsafe { <T::Ptr as ForeignOwnable>::borrow(private) };
284
285 // SAFETY:
286 // * The file is valid for the duration of this call.
287 // * There is no active fdget_pos region on the file on this thread.
288 let file = unsafe { File::from_raw_file(file) };
289
290 match T::ioctl(device, file, cmd, arg) {
291 Ok(ret) => ret as c_long,
292 Err(err) => err.to_errno() as c_long,
293 }
294 }
295
296 /// # Safety
297 ///
298 /// `file` must be a valid file that is associated with a `MiscDeviceRegistration<T>`.
299 #[cfg(CONFIG_COMPAT)]
300 unsafe extern "C" fn compat_ioctl(
301 file: *mut bindings::file,
302 cmd: c_uint,
303 arg: c_ulong,
304 ) -> c_long {
305 // SAFETY: The compat ioctl call of a file can access the private data.
306 let private = unsafe { (*file).private_data }.cast();
307 // SAFETY: Ioctl calls can borrow the private data of the file.
308 let device = unsafe { <T::Ptr as ForeignOwnable>::borrow(private) };
309
310 // SAFETY:
311 // * The file is valid for the duration of this call.
312 // * There is no active fdget_pos region on the file on this thread.
313 let file = unsafe { File::from_raw_file(file) };
314
315 match T::compat_ioctl(device, file, cmd, arg) {
316 Ok(ret) => ret as c_long,
317 Err(err) => err.to_errno() as c_long,
318 }
319 }
320
321 /// # Safety
322 ///
323 /// - `file` must be a valid file that is associated with a `MiscDeviceRegistration<T>`.
324 /// - `seq_file` must be a valid `struct seq_file` that we can write to.
325 unsafe extern "C" fn show_fdinfo(seq_file: *mut bindings::seq_file, file: *mut bindings::file) {
326 // SAFETY: The release call of a file owns the private data.
327 let private = unsafe { (*file).private_data }.cast();
328 // SAFETY: Ioctl calls can borrow the private data of the file.
329 let device = unsafe { <T::Ptr as ForeignOwnable>::borrow(private) };
330 // SAFETY:
331 // * The file is valid for the duration of this call.
332 // * There is no active fdget_pos region on the file on this thread.
333 let file = unsafe { File::from_raw_file(file) };
334 // SAFETY: The caller ensures that the pointer is valid and exclusive for the duration in
335 // which this method is called.
336 let m = unsafe { SeqFile::from_raw(seq_file) };
337
338 T::show_fdinfo(device, m, file);
339 }
340
341 const VTABLE: bindings::file_operations = bindings::file_operations {
342 open: Some(Self::open),
343 release: Some(Self::release),
344 mmap: if T::HAS_MMAP { Some(Self::mmap) } else { None },
345 unlocked_ioctl: if T::HAS_IOCTL {
346 Some(Self::ioctl)
347 } else {
348 None
349 },
350 #[cfg(CONFIG_COMPAT)]
351 compat_ioctl: if T::HAS_COMPAT_IOCTL {
352 Some(Self::compat_ioctl)
353 } else if T::HAS_IOCTL {
354 Some(bindings::compat_ptr_ioctl)
355 } else {
356 None
357 },
358 show_fdinfo: if T::HAS_SHOW_FDINFO {
359 Some(Self::show_fdinfo)
360 } else {
361 None
362 },
363 // SAFETY: All zeros is a valid value for `bindings::file_operations`.
364 ..unsafe { MaybeUninit::zeroed().assume_init() }
365 };
366
367 const fn build() -> &'static bindings::file_operations {
368 &Self::VTABLE
369 }
370}