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