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