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// SPDX-License-Identifier: GPL-2.0
// Copyright (C) 2024 Google LLC.
//! Miscdevice support.
//!
//! C headers: [`include/linux/miscdevice.h`](srctree/include/linux/miscdevice.h).
//!
//! Reference: <https://www.kernel.org/doc/html/latest/driver-api/misc_devices.html>
use crate::{
bindings,
device::Device,
error::{to_result, Error, Result, VTABLE_DEFAULT_ERROR},
ffi::{c_int, c_long, c_uint, c_ulong},
fs::File,
prelude::*,
seq_file::SeqFile,
str::CStr,
types::{ForeignOwnable, Opaque},
};
use core::{marker::PhantomData, mem::MaybeUninit, pin::Pin};
/// Options for creating a misc device.
#[derive(Copy, Clone)]
pub struct MiscDeviceOptions {
/// The name of the miscdevice.
pub name: &'static CStr,
}
impl MiscDeviceOptions {
/// Create a raw `struct miscdev` ready for registration.
pub const fn into_raw<T: MiscDevice>(self) -> bindings::miscdevice {
// SAFETY: All zeros is valid for this C type.
let mut result: bindings::miscdevice = unsafe { MaybeUninit::zeroed().assume_init() };
result.minor = bindings::MISC_DYNAMIC_MINOR as _;
result.name = self.name.as_char_ptr();
result.fops = create_vtable::<T>();
result
}
}
/// A registration of a miscdevice.
///
/// # Invariants
///
/// `inner` is a registered misc device.
#[repr(transparent)]
#[pin_data(PinnedDrop)]
pub struct MiscDeviceRegistration<T> {
#[pin]
inner: Opaque<bindings::miscdevice>,
_t: PhantomData<T>,
}
// SAFETY: It is allowed to call `misc_deregister` on a different thread from where you called
// `misc_register`.
unsafe impl<T> Send for MiscDeviceRegistration<T> {}
// SAFETY: All `&self` methods on this type are written to ensure that it is safe to call them in
// parallel.
unsafe impl<T> Sync for MiscDeviceRegistration<T> {}
impl<T: MiscDevice> MiscDeviceRegistration<T> {
/// Register a misc device.
pub fn register(opts: MiscDeviceOptions) -> impl PinInit<Self, Error> {
try_pin_init!(Self {
inner <- Opaque::try_ffi_init(move |slot: *mut bindings::miscdevice| {
// SAFETY: The initializer can write to the provided `slot`.
unsafe { slot.write(opts.into_raw::<T>()) };
// SAFETY: We just wrote the misc device options to the slot. The miscdevice will
// get unregistered before `slot` is deallocated because the memory is pinned and
// the destructor of this type deallocates the memory.
// INVARIANT: If this returns `Ok(())`, then the `slot` will contain a registered
// misc device.
to_result(unsafe { bindings::misc_register(slot) })
}),
_t: PhantomData,
})
}
/// Returns a raw pointer to the misc device.
pub fn as_raw(&self) -> *mut bindings::miscdevice {
self.inner.get()
}
/// Access the `this_device` field.
pub fn device(&self) -> &Device {
// SAFETY: This can only be called after a successful register(), which always
// initialises `this_device` with a valid device. Furthermore, the signature of this
// function tells the borrow-checker that the `&Device` reference must not outlive the
// `&MiscDeviceRegistration<T>` used to obtain it, so the last use of the reference must be
// before the underlying `struct miscdevice` is destroyed.
unsafe { Device::as_ref((*self.as_raw()).this_device) }
}
}
#[pinned_drop]
impl<T> PinnedDrop for MiscDeviceRegistration<T> {
fn drop(self: Pin<&mut Self>) {
// SAFETY: We know that the device is registered by the type invariants.
unsafe { bindings::misc_deregister(self.inner.get()) };
}
}
/// Trait implemented by the private data of an open misc device.
#[vtable]
pub trait MiscDevice: Sized {
/// What kind of pointer should `Self` be wrapped in.
type Ptr: ForeignOwnable + Send + Sync;
/// Called when the misc device is opened.
///
/// The returned pointer will be stored as the private data for the file.
fn open(_file: &File, _misc: &MiscDeviceRegistration<Self>) -> Result<Self::Ptr>;
/// Called when the misc device is released.
fn release(device: Self::Ptr, _file: &File) {
drop(device);
}
/// Handler for ioctls.
///
/// The `cmd` argument is usually manipulated using the utilties in [`kernel::ioctl`].
///
/// [`kernel::ioctl`]: mod@crate::ioctl
fn ioctl(
_device: <Self::Ptr as ForeignOwnable>::Borrowed<'_>,
_file: &File,
_cmd: u32,
_arg: usize,
) -> Result<isize> {
build_error!(VTABLE_DEFAULT_ERROR)
}
/// Handler for ioctls.
///
/// Used for 32-bit userspace on 64-bit platforms.
///
/// This method is optional and only needs to be provided if the ioctl relies on structures
/// that have different layout on 32-bit and 64-bit userspace. If no implementation is
/// provided, then `compat_ptr_ioctl` will be used instead.
#[cfg(CONFIG_COMPAT)]
fn compat_ioctl(
_device: <Self::Ptr as ForeignOwnable>::Borrowed<'_>,
_file: &File,
_cmd: u32,
_arg: usize,
) -> Result<isize> {
build_error!(VTABLE_DEFAULT_ERROR)
}
/// Show info for this fd.
fn show_fdinfo(
_device: <Self::Ptr as ForeignOwnable>::Borrowed<'_>,
_m: &SeqFile,
_file: &File,
) {
build_error!(VTABLE_DEFAULT_ERROR)
}
}
const fn create_vtable<T: MiscDevice>() -> &'static bindings::file_operations {
const fn maybe_fn<T: Copy>(check: bool, func: T) -> Option<T> {
if check {
Some(func)
} else {
None
}
}
struct VtableHelper<T: MiscDevice> {
_t: PhantomData<T>,
}
impl<T: MiscDevice> VtableHelper<T> {
const VTABLE: bindings::file_operations = bindings::file_operations {
open: Some(fops_open::<T>),
release: Some(fops_release::<T>),
unlocked_ioctl: maybe_fn(T::HAS_IOCTL, fops_ioctl::<T>),
#[cfg(CONFIG_COMPAT)]
compat_ioctl: if T::HAS_COMPAT_IOCTL {
Some(fops_compat_ioctl::<T>)
} else if T::HAS_IOCTL {
Some(bindings::compat_ptr_ioctl)
} else {
None
},
show_fdinfo: maybe_fn(T::HAS_SHOW_FDINFO, fops_show_fdinfo::<T>),
// SAFETY: All zeros is a valid value for `bindings::file_operations`.
..unsafe { MaybeUninit::zeroed().assume_init() }
};
}
&VtableHelper::<T>::VTABLE
}
/// # Safety
///
/// `file` and `inode` must be the file and inode for a file that is undergoing initialization.
/// The file must be associated with a `MiscDeviceRegistration<T>`.
unsafe extern "C" fn fops_open<T: MiscDevice>(
inode: *mut bindings::inode,
raw_file: *mut bindings::file,
) -> c_int {
// SAFETY: The pointers are valid and for a file being opened.
let ret = unsafe { bindings::generic_file_open(inode, raw_file) };
if ret != 0 {
return ret;
}
// SAFETY: The open call of a file can access the private data.
let misc_ptr = unsafe { (*raw_file).private_data };
// SAFETY: This is a miscdevice, so `misc_open()` set the private data to a pointer to the
// associated `struct miscdevice` before calling into this method. Furthermore, `misc_open()`
// ensures that the miscdevice can't be unregistered and freed during this call to `fops_open`.
let misc = unsafe { &*misc_ptr.cast::<MiscDeviceRegistration<T>>() };
// SAFETY:
// * This underlying file is valid for (much longer than) the duration of `T::open`.
// * There is no active fdget_pos region on the file on this thread.
let file = unsafe { File::from_raw_file(raw_file) };
let ptr = match T::open(file, misc) {
Ok(ptr) => ptr,
Err(err) => return err.to_errno(),
};
// This overwrites the private data with the value specified by the user, changing the type of
// this file's private data. All future accesses to the private data is performed by other
// fops_* methods in this file, which all correctly cast the private data to the new type.
//
// SAFETY: The open call of a file can access the private data.
unsafe { (*raw_file).private_data = ptr.into_foreign() };
0
}
/// # Safety
///
/// `file` and `inode` must be the file and inode for a file that is being released. The file must
/// be associated with a `MiscDeviceRegistration<T>`.
unsafe extern "C" fn fops_release<T: MiscDevice>(
_inode: *mut bindings::inode,
file: *mut bindings::file,
) -> c_int {
// SAFETY: The release call of a file owns the private data.
let private = unsafe { (*file).private_data };
// SAFETY: The release call of a file owns the private data.
let ptr = unsafe { <T::Ptr as ForeignOwnable>::from_foreign(private) };
// SAFETY:
// * The file is valid for the duration of this call.
// * There is no active fdget_pos region on the file on this thread.
T::release(ptr, unsafe { File::from_raw_file(file) });
0
}
/// # Safety
///
/// `file` must be a valid file that is associated with a `MiscDeviceRegistration<T>`.
unsafe extern "C" fn fops_ioctl<T: MiscDevice>(
file: *mut bindings::file,
cmd: c_uint,
arg: c_ulong,
) -> c_long {
// SAFETY: The ioctl call of a file can access the private data.
let private = unsafe { (*file).private_data };
// SAFETY: Ioctl calls can borrow the private data of the file.
let device = unsafe { <T::Ptr as ForeignOwnable>::borrow(private) };
// SAFETY:
// * The file is valid for the duration of this call.
// * There is no active fdget_pos region on the file on this thread.
let file = unsafe { File::from_raw_file(file) };
match T::ioctl(device, file, cmd, arg) {
Ok(ret) => ret as c_long,
Err(err) => err.to_errno() as c_long,
}
}
/// # Safety
///
/// `file` must be a valid file that is associated with a `MiscDeviceRegistration<T>`.
#[cfg(CONFIG_COMPAT)]
unsafe extern "C" fn fops_compat_ioctl<T: MiscDevice>(
file: *mut bindings::file,
cmd: c_uint,
arg: c_ulong,
) -> c_long {
// SAFETY: The compat ioctl call of a file can access the private data.
let private = unsafe { (*file).private_data };
// SAFETY: Ioctl calls can borrow the private data of the file.
let device = unsafe { <T::Ptr as ForeignOwnable>::borrow(private) };
// SAFETY:
// * The file is valid for the duration of this call.
// * There is no active fdget_pos region on the file on this thread.
let file = unsafe { File::from_raw_file(file) };
match T::compat_ioctl(device, file, cmd, arg) {
Ok(ret) => ret as c_long,
Err(err) => err.to_errno() as c_long,
}
}
/// # Safety
///
/// - `file` must be a valid file that is associated with a `MiscDeviceRegistration<T>`.
/// - `seq_file` must be a valid `struct seq_file` that we can write to.
unsafe extern "C" fn fops_show_fdinfo<T: MiscDevice>(
seq_file: *mut bindings::seq_file,
file: *mut bindings::file,
) {
// SAFETY: The release call of a file owns the private data.
let private = unsafe { (*file).private_data };
// SAFETY: Ioctl calls can borrow the private data of the file.
let device = unsafe { <T::Ptr as ForeignOwnable>::borrow(private) };
// SAFETY:
// * The file is valid for the duration of this call.
// * There is no active fdget_pos region on the file on this thread.
let file = unsafe { File::from_raw_file(file) };
// SAFETY: The caller ensures that the pointer is valid and exclusive for the duration in which
// this method is called.
let m = unsafe { SeqFile::from_raw(seq_file) };
T::show_fdinfo(device, m, file);
}
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