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// SPDX-License-Identifier: GPL-2.0
// Copyright (C) 2024 Google LLC.
//! Kernel IO callbacks.
//!
//! C headers: [`include/linux/fs.h`](srctree/include/linux/fs.h)
use core::marker::PhantomData;
use core::ptr::NonNull;
use kernel::types::ForeignOwnable;
/// Wrapper for the kernel's `struct kiocb`.
///
/// Currently this abstractions is incomplete and is essentially just a tuple containing a
/// reference to a file and a file position.
///
/// The type `T` represents the filesystem or driver specific data associated with the file.
///
/// # Invariants
///
/// `inner` points at a valid `struct kiocb` whose file has the type `T` as its private data.
pub struct Kiocb<'a, T> {
inner: NonNull<bindings::kiocb>,
_phantom: PhantomData<&'a T>,
}
impl<'a, T: ForeignOwnable> Kiocb<'a, T> {
/// Create a `Kiocb` from a raw pointer.
///
/// # Safety
///
/// The pointer must reference a valid `struct kiocb` for the duration of `'a`. The private
/// data of the file must be `T`.
pub unsafe fn from_raw(kiocb: *mut bindings::kiocb) -> Self {
Self {
// SAFETY: If a pointer is valid it is not null.
inner: unsafe { NonNull::new_unchecked(kiocb) },
_phantom: PhantomData,
}
}
/// Access the underlying `struct kiocb` directly.
pub fn as_raw(&self) -> *mut bindings::kiocb {
self.inner.as_ptr()
}
/// Get the filesystem or driver specific data associated with the file.
pub fn file(&self) -> <T as ForeignOwnable>::Borrowed<'a> {
// SAFETY: We have shared access to this kiocb and hence the underlying file, so we can
// read the file's private data.
let private = unsafe { (*(*self.as_raw()).ki_filp).private_data };
// SAFETY: The kiocb has shared access to the private data.
unsafe { <T as ForeignOwnable>::borrow(private) }
}
/// Gets the current value of `ki_pos`.
pub fn ki_pos(&self) -> i64 {
// SAFETY: We have shared access to the kiocb, so we can read its `ki_pos` field.
unsafe { (*self.as_raw()).ki_pos }
}
/// Gets a mutable reference to the `ki_pos` field.
pub fn ki_pos_mut(&mut self) -> &mut i64 {
// SAFETY: We have exclusive access to the kiocb, so we can write to `ki_pos`.
unsafe { &mut (*self.as_raw()).ki_pos }
}
}
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