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file_operations.rs
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file_operations.rs
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// SPDX-License-Identifier: GPL-2.0
//! File operations.
//!
//! C header: [`include/linux/fs.h`](../../../../include/linux/fs.h)
use core::convert::{TryFrom, TryInto};
use core::{marker, mem, ptr};
use alloc::boxed::Box;
use alloc::sync::Arc;
use crate::bindings;
use crate::c_types;
use crate::error::{Error, KernelResult};
use crate::sync::{Ref, RefCounted};
use crate::user_ptr::{UserSlicePtr, UserSlicePtrReader, UserSlicePtrWriter};
/// Wraps the kernel's `struct file`.
///
/// # Invariants
///
/// The pointer [`File::ptr`] is non-null and valid.
pub struct File {
ptr: *const bindings::file,
}
impl File {
/// Constructs a new [`struct file`] wrapper.
///
/// # Safety
///
/// The pointer `ptr` must be non-null and valid for the lifetime of the object.
unsafe fn from_ptr(ptr: *const bindings::file) -> File {
// INVARIANTS: the safety contract ensures the type invariant will hold.
File { ptr }
}
/// Returns the current seek/cursor/pointer position (`struct file::f_pos`).
pub fn pos(&self) -> u64 {
// SAFETY: `File::ptr` is guaranteed to be valid by the type invariants.
unsafe { (*self.ptr).f_pos as u64 }
}
/// Returns whether the file is in blocking mode.
pub fn is_blocking(&self) -> bool {
// SAFETY: `File::ptr` is guaranteed to be valid by the type invariants.
unsafe { (*self.ptr).f_flags & bindings::O_NONBLOCK == 0 }
}
}
/// Equivalent to [`std::io::SeekFrom`].
///
/// [`std::io::SeekFrom`]: https://doc.rust-lang.org/std/io/enum.SeekFrom.html
pub enum SeekFrom {
/// Equivalent to C's `SEEK_SET`.
Start(u64),
/// Equivalent to C's `SEEK_END`.
End(i64),
/// Equivalent to C's `SEEK_CUR`.
Current(i64),
}
fn from_kernel_result<T>(r: KernelResult<T>) -> T
where
T: TryFrom<c_types::c_int>,
T::Error: core::fmt::Debug,
{
match r {
Ok(v) => v,
Err(e) => T::try_from(e.to_kernel_errno()).unwrap(),
}
}
macro_rules! from_kernel_result {
($($tt:tt)*) => {{
from_kernel_result((|| {
$($tt)*
})())
}};
}
unsafe extern "C" fn open_callback<A: FileOpenAdapter, T: FileOpener<A::Arg>>(
inode: *mut bindings::inode,
file: *mut bindings::file,
) -> c_types::c_int {
from_kernel_result! {
let arg = A::convert(inode, file);
let ptr = T::open(&*arg)?.into_pointer();
(*file).private_data = ptr as *mut c_types::c_void;
Ok(0)
}
}
unsafe extern "C" fn read_callback<T: FileOperations>(
file: *mut bindings::file,
buf: *mut c_types::c_char,
len: c_types::c_size_t,
offset: *mut bindings::loff_t,
) -> c_types::c_ssize_t {
from_kernel_result! {
let mut data = UserSlicePtr::new(buf as *mut c_types::c_void, len).writer();
let f = &*((*file).private_data as *const T);
// No `FMODE_UNSIGNED_OFFSET` support, so `offset` must be in [0, 2^63).
// See discussion in https://github.com/fishinabarrel/linux-kernel-module-rust/pull/113
let read = f.read(&File::from_ptr(file), &mut data, (*offset).try_into()?)?;
(*offset) += bindings::loff_t::try_from(read).unwrap();
Ok(read as _)
}
}
unsafe extern "C" fn write_callback<T: FileOperations>(
file: *mut bindings::file,
buf: *const c_types::c_char,
len: c_types::c_size_t,
offset: *mut bindings::loff_t,
) -> c_types::c_ssize_t {
from_kernel_result! {
let mut data = UserSlicePtr::new(buf as *mut c_types::c_void, len).reader();
let f = &*((*file).private_data as *const T);
// No `FMODE_UNSIGNED_OFFSET` support, so `offset` must be in [0, 2^63).
// See discussion in https://github.com/fishinabarrel/linux-kernel-module-rust/pull/113
let written = f.write(&mut data, (*offset).try_into()?)?;
(*offset) += bindings::loff_t::try_from(written).unwrap();
Ok(written as _)
}
}
unsafe extern "C" fn release_callback<T: FileOperations>(
_inode: *mut bindings::inode,
file: *mut bindings::file,
) -> c_types::c_int {
let ptr = mem::replace(&mut (*file).private_data, ptr::null_mut());
T::release(T::Wrapper::from_pointer(ptr as _), &File::from_ptr(file));
0
}
unsafe extern "C" fn llseek_callback<T: FileOperations>(
file: *mut bindings::file,
offset: bindings::loff_t,
whence: c_types::c_int,
) -> bindings::loff_t {
from_kernel_result! {
let off = match whence as u32 {
bindings::SEEK_SET => SeekFrom::Start(offset.try_into()?),
bindings::SEEK_CUR => SeekFrom::Current(offset),
bindings::SEEK_END => SeekFrom::End(offset),
_ => return Err(Error::EINVAL),
};
let f = &*((*file).private_data as *const T);
let off = f.seek(&File::from_ptr(file), off)?;
Ok(off as bindings::loff_t)
}
}
unsafe extern "C" fn unlocked_ioctl_callback<T: FileOperations>(
file: *mut bindings::file,
cmd: c_types::c_uint,
arg: c_types::c_ulong,
) -> c_types::c_long {
from_kernel_result! {
let f = &*((*file).private_data as *const T);
// SAFETY: This function is called by the kernel, so it must set `fs` appropriately.
let mut cmd = IoctlCommand::new(cmd as _, arg as _);
let ret = f.ioctl(&File::from_ptr(file), &mut cmd)?;
Ok(ret as _)
}
}
unsafe extern "C" fn compat_ioctl_callback<T: FileOperations>(
file: *mut bindings::file,
cmd: c_types::c_uint,
arg: c_types::c_ulong,
) -> c_types::c_long {
from_kernel_result! {
let f = &*((*file).private_data as *const T);
// SAFETY: This function is called by the kernel, so it must set `fs` appropriately.
let mut cmd = IoctlCommand::new(cmd as _, arg as _);
let ret = f.compat_ioctl(&File::from_ptr(file), &mut cmd)?;
Ok(ret as _)
}
}
unsafe extern "C" fn fsync_callback<T: FileOperations>(
file: *mut bindings::file,
start: bindings::loff_t,
end: bindings::loff_t,
datasync: c_types::c_int,
) -> c_types::c_int {
from_kernel_result! {
let start = start.try_into()?;
let end = end.try_into()?;
let datasync = datasync != 0;
let f = &*((*file).private_data as *const T);
let res = f.fsync(&File::from_ptr(file), start, end, datasync)?;
Ok(res.try_into().unwrap())
}
}
pub(crate) struct FileOperationsVtable<A, T>(marker::PhantomData<A>, marker::PhantomData<T>);
impl<A: FileOpenAdapter, T: FileOpener<A::Arg>> FileOperationsVtable<A, T> {
const VTABLE: bindings::file_operations = bindings::file_operations {
open: Some(open_callback::<A, T>),
release: Some(release_callback::<T>),
read: if T::TO_USE.read {
Some(read_callback::<T>)
} else {
None
},
write: if T::TO_USE.write {
Some(write_callback::<T>)
} else {
None
},
llseek: if T::TO_USE.seek {
Some(llseek_callback::<T>)
} else {
None
},
check_flags: None,
compat_ioctl: if T::TO_USE.compat_ioctl {
Some(compat_ioctl_callback::<T>)
} else {
None
},
copy_file_range: None,
fallocate: None,
fadvise: None,
fasync: None,
flock: None,
flush: None,
fsync: if T::TO_USE.fsync {
Some(fsync_callback::<T>)
} else {
None
},
get_unmapped_area: None,
iterate: None,
iterate_shared: None,
iopoll: None,
lock: None,
mmap: None,
mmap_supported_flags: 0,
owner: ptr::null_mut(),
poll: None,
read_iter: None,
remap_file_range: None,
sendpage: None,
setlease: None,
show_fdinfo: None,
splice_read: None,
splice_write: None,
unlocked_ioctl: if T::TO_USE.ioctl {
Some(unlocked_ioctl_callback::<T>)
} else {
None
},
write_iter: None,
};
/// Builds an instance of [`struct file_operations`].
///
/// # Safety
///
/// The caller must ensure that the adapter is compatible with the way the device is registered.
pub(crate) const unsafe fn build() -> &'static bindings::file_operations {
&Self::VTABLE
}
}
/// Represents which fields of [`struct file_operations`] should be populated with pointers.
pub struct ToUse {
/// The `read` field of [`struct file_operations`].
pub read: bool,
/// The `write` field of [`struct file_operations`].
pub write: bool,
/// The `llseek` field of [`struct file_operations`].
pub seek: bool,
/// The `unlocked_ioctl` field of [`struct file_operations`].
pub ioctl: bool,
/// The `compat_ioctl` field of [`struct file_operations`].
pub compat_ioctl: bool,
/// The `fsync` field of [`struct file_operations`].
pub fsync: bool,
}
/// A constant version where all values are to set to `false`, that is, all supported fields will
/// be set to null pointers.
pub const USE_NONE: ToUse = ToUse {
read: false,
write: false,
seek: false,
ioctl: false,
compat_ioctl: false,
fsync: false,
};
/// Defines the [`FileOperations::TO_USE`] field based on a list of fields to be populated.
#[macro_export]
macro_rules! declare_file_operations {
() => {
const TO_USE: $crate::file_operations::ToUse = $crate::file_operations::USE_NONE;
};
($($i:ident),+) => {
const TO_USE: kernel::file_operations::ToUse =
$crate::file_operations::ToUse {
$($i: true),+ ,
..$crate::file_operations::USE_NONE
};
};
}
/// Allows the handling of ioctls defined with the `_IO`, `_IOR`, `_IOW`, and `_IOWR` macros.
///
/// For each macro, there is a handler function that takes the appropriate types as arguments.
pub trait IoctlHandler: Sync {
/// Handles ioctls defined with the `_IO` macro, that is, with no buffer as argument.
fn pure(&self, _file: &File, _cmd: u32, _arg: usize) -> KernelResult<i32> {
Err(Error::EINVAL)
}
/// Handles ioctls defined with the `_IOR` macro, that is, with an output buffer provided as
/// argument.
fn read(&self, _file: &File, _cmd: u32, _writer: &mut UserSlicePtrWriter) -> KernelResult<i32> {
Err(Error::EINVAL)
}
/// Handles ioctls defined with the `_IOW` macro, that is, with an input buffer provided as
/// argument.
fn write(
&self,
_file: &File,
_cmd: u32,
_reader: &mut UserSlicePtrReader,
) -> KernelResult<i32> {
Err(Error::EINVAL)
}
/// Handles ioctls defined with the `_IOWR` macro, that is, with a buffer for both input and
/// output provided as argument.
fn read_write(&self, _file: &File, _cmd: u32, _data: UserSlicePtr) -> KernelResult<i32> {
Err(Error::EINVAL)
}
}
/// Represents an ioctl command.
///
/// It can use the components of an ioctl command to dispatch ioctls using
/// [`IoctlCommand::dispatch`].
pub struct IoctlCommand {
cmd: u32,
arg: usize,
user_slice: Option<UserSlicePtr>,
}
impl IoctlCommand {
/// Constructs a new [`IoctlCommand`].
fn new(cmd: u32, arg: usize) -> Self {
let size = (cmd >> bindings::_IOC_SIZESHIFT) & bindings::_IOC_SIZEMASK;
// SAFETY: We only create one instance of the user slice per ioctl call, so TOCTOU issues
// are not possible.
let user_slice = Some(unsafe { UserSlicePtr::new(arg as _, size as _) });
Self {
cmd,
arg,
user_slice,
}
}
/// Dispatches the given ioctl to the appropriate handler based on the value of the command. It
/// also creates a [`UserSlicePtr`], [`UserSlicePtrReader`], or [`UserSlicePtrWriter`]
/// depending on the direction of the buffer of the command.
///
/// It is meant to be used in implementations of [`FileOperations::ioctl`] and
/// [`FileOperations::compat_ioctl`].
pub fn dispatch<T: IoctlHandler>(&mut self, handler: &T, file: &File) -> KernelResult<i32> {
let dir = (self.cmd >> bindings::_IOC_DIRSHIFT) & bindings::_IOC_DIRMASK;
if dir == bindings::_IOC_NONE {
return handler.pure(file, self.cmd, self.arg);
}
let data = self.user_slice.take().ok_or(Error::EINVAL)?;
const READ_WRITE: u32 = bindings::_IOC_READ | bindings::_IOC_WRITE;
match dir {
bindings::_IOC_WRITE => handler.write(file, self.cmd, &mut data.reader()),
bindings::_IOC_READ => handler.read(file, self.cmd, &mut data.writer()),
READ_WRITE => handler.read_write(file, self.cmd, data),
_ => Err(Error::EINVAL),
}
}
/// Returns the raw 32-bit value of the command and the ptr-sized argument.
pub fn raw(&self) -> (u32, usize) {
(self.cmd, self.arg)
}
}
/// Trait for extracting file open arguments from kernel data structures.
///
/// This is meant to be implemented by registration managers.
pub trait FileOpenAdapter {
/// The type of argument this adapter extracts.
type Arg;
/// Converts untyped data stored in [`struct inode`] and [`struct file`] (when [`struct
/// file_operations::open`] is called) into the given type. For example, for `miscdev`
/// devices, a pointer to the registered [`struct miscdev`] is stored in [`struct
/// file::private_data`].
///
/// # Safety
///
/// This function must be called only when [`struct file_operations::open`] is being called for
/// a file that was registered by the implementer.
unsafe fn convert(_inode: *mut bindings::inode, _file: *mut bindings::file)
-> *const Self::Arg;
}
/// Trait for implementers of kernel files.
///
/// In addition to the methods in [`FileOperations`], implementers must also provide
/// [`FileOpener::open`] with a customised argument. This allows a single implementation of
/// [`FileOperations`] to be used for different types of registrations, for example, `miscdev` and
/// `chrdev`.
pub trait FileOpener<T: ?Sized>: FileOperations {
/// Creates a new instance of this file.
///
/// Corresponds to the `open` function pointer in `struct file_operations`.
fn open(context: &T) -> KernelResult<Self::Wrapper>;
}
/// Corresponds to the kernel's `struct file_operations`.
///
/// You implement this trait whenever you would create a `struct file_operations`.
///
/// File descriptors may be used from multiple threads/processes concurrently, so your type must be
/// [`Sync`]. It must also be [`Send`] because [`FileOperations::release`] will be called from the
/// thread that decrements that associated file's refcount to zero.
pub trait FileOperations: Send + Sync + Sized {
/// The methods to use to populate [`struct file_operations`].
const TO_USE: ToUse;
/// The pointer type that will be used to hold ourselves.
type Wrapper: PointerWrapper<Self>;
/// Cleans up after the last reference to the file goes away.
///
/// Note that the object is moved, so it will be freed automatically unless the implementation
/// moves it elsewhere.
///
/// Corresponds to the `release` function pointer in `struct file_operations`.
fn release(_obj: Self::Wrapper, _file: &File) {}
/// Reads data from this file to userspace.
///
/// Corresponds to the `read` function pointer in `struct file_operations`.
fn read(
&self,
_file: &File,
_data: &mut UserSlicePtrWriter,
_offset: u64,
) -> KernelResult<usize> {
Err(Error::EINVAL)
}
/// Writes data from userspace to this file.
///
/// Corresponds to the `write` function pointer in `struct file_operations`.
fn write(&self, _data: &mut UserSlicePtrReader, _offset: u64) -> KernelResult<usize> {
Err(Error::EINVAL)
}
/// Changes the position of the file.
///
/// Corresponds to the `llseek` function pointer in `struct file_operations`.
fn seek(&self, _file: &File, _offset: SeekFrom) -> KernelResult<u64> {
Err(Error::EINVAL)
}
/// Performs IO control operations that are specific to the file.
///
/// Corresponds to the `unlocked_ioctl` function pointer in `struct file_operations`.
fn ioctl(&self, _file: &File, _cmd: &mut IoctlCommand) -> KernelResult<i32> {
Err(Error::EINVAL)
}
/// Performs 32-bit IO control operations on that are specific to the file on 64-bit kernels.
///
/// Corresponds to the `compat_ioctl` function pointer in `struct file_operations`.
fn compat_ioctl(&self, _file: &File, _cmd: &mut IoctlCommand) -> KernelResult<i32> {
Err(Error::EINVAL)
}
/// Syncs pending changes to this file.
///
/// Corresponds to the `fsync` function pointer in `struct file_operations`.
fn fsync(&self, _file: &File, _start: u64, _end: u64, _datasync: bool) -> KernelResult<u32> {
Err(Error::EINVAL)
}
}
/// Used to convert an object into a raw pointer that represents it.
///
/// It can eventually be converted back into the object. This is used to store objects as pointers
/// in kernel data structures, for example, an implementation of [`FileOperations`] in `struct
/// file::private_data`.
pub trait PointerWrapper<T> {
/// Returns the raw pointer.
fn into_pointer(self) -> *const T;
/// Returns the instance back from the raw pointer.
///
/// # Safety
///
/// The passed pointer must come from a previous call to [`PointerWrapper::into_pointer()`].
unsafe fn from_pointer(ptr: *const T) -> Self;
}
impl<T> PointerWrapper<T> for Box<T> {
fn into_pointer(self) -> *const T {
Box::into_raw(self)
}
unsafe fn from_pointer(ptr: *const T) -> Self {
Box::from_raw(ptr as _)
}
}
impl<T: RefCounted> PointerWrapper<T> for Ref<T> {
fn into_pointer(self) -> *const T {
Ref::into_raw(self)
}
unsafe fn from_pointer(ptr: *const T) -> Self {
Ref::from_raw(ptr as _)
}
}
impl<T> PointerWrapper<T> for Arc<T> {
fn into_pointer(self) -> *const T {
Arc::into_raw(self)
}
unsafe fn from_pointer(ptr: *const T) -> Self {
Arc::from_raw(ptr)
}
}