// SPDX-License-Identifier: GPL-2.0 //! Implementation of [`Box`]. #[allow(unused_imports)] // Used in doc comments.use super::allocator::{KVmalloc, Kmalloc, Vmalloc};use super::{AllocError, Allocator, Flags};use core::alloc::Layout;use core::fmt;use core::marker::PhantomData;use core::mem::ManuallyDrop;use core::mem::MaybeUninit;use core::ops::{Deref, DerefMut};use core::pin::Pin;use core::ptr::NonNull;use core::result::Result; use crate::init::InPlaceInit;use crate::types::ForeignOwnable;use pin_init::{InPlaceWrite, Init, PinInit, ZeroableOption}; /// The kernel's [`Box`] type -- a heap allocation for a single value of type `T`.////// This is the kernel's version of the Rust stdlib's `Box`. There are several differences,/// for example no `noalias` attribute is emitted and partially moving out of a `Box` is not/// supported. There are also several API differences, e.g. `Box` always requires an [`Allocator`]/// implementation to be passed as generic, page [`Flags`] when allocating memory and all functions/// that may allocate memory are fallible.////// `Box` works with any of the kernel's allocators, e.g. [`Kmalloc`], [`Vmalloc`] or [`KVmalloc`]./// There are aliases for `Box` with these allocators ([`KBox`], [`VBox`], [`KVBox`]).////// When dropping a [`Box`], the value is also dropped and the heap memory is automatically freed.////// # Examples////// ```/// let b = KBox::<u64>::new(24_u64, GFP_KERNEL)?;////// assert_eq!(*b, 24_u64);/// # Ok::<(), Error>(())/// ```////// ```/// # use kernel::bindings;/// const SIZE: usize = bindings::KMALLOC_MAX_SIZE as usize + 1;/// struct Huge([u8; SIZE]);////// assert!(KBox::<Huge>::new_uninit(GFP_KERNEL | __GFP_NOWARN).is_err());/// ```////// ```/// # use kernel::bindings;/// const SIZE: usize = bindings::KMALLOC_MAX_SIZE as usize + 1;/// struct Huge([u8; SIZE]);////// assert!(KVBox::<Huge>::new_uninit(GFP_KERNEL).is_ok());/// ```////// [`Box`]es can also be used to store trait objects by coercing their type:////// ```/// trait FooTrait {}////// struct FooStruct;/// impl FooTrait for FooStruct {}////// let _ = KBox::new(FooStruct, GFP_KERNEL)? as KBox<dyn FooTrait>;/// # Ok::<(), Error>(())/// ```////// # Invariants////// `self.0` is always properly aligned and either points to memory allocated with `A` or, for/// zero-sized types, is a dangling, well aligned pointer.#[repr(transparent)]#[cfg_attr(CONFIG_RUSTC_HAS_COERCE_POINTEE, derive(core::marker::CoercePointee))]pub struct Box<#[cfg_attr(CONFIG_RUSTC_HAS_COERCE_POINTEE, pointee)] T: ?Sized, A: Allocator>(    NonNull<T>,    PhantomData<A>,); // This is to allow coercion from `Box<T, A>` to `Box<U, A>` if `T` can be converted to the// dynamically-sized type (DST) `U`.#[cfg(not(CONFIG_RUSTC_HAS_COERCE_POINTEE))]impl<T, U, A> core::ops::CoerceUnsized<Box<U, A>> for Box<T, A>where    T: ?Sized + core::marker::Unsize<U>,    U: ?Sized,    A: Allocator,{} // This is to allow `Box<U, A>` to be dispatched on when `Box<T, A>` can be coerced into `Box<U,// A>`.#[cfg(not(CONFIG_RUSTC_HAS_COERCE_POINTEE))]impl<T, U, A> core::ops::DispatchFromDyn<Box<U, A>> for Box<T, A>where    T: ?Sized + core::marker::Unsize<U>,    U: ?Sized,    A: Allocator,{} /// Type alias for [`Box`] with a [`Kmalloc`] allocator.////// # Examples////// ```/// let b = KBox::new(24_u64, GFP_KERNEL)?;////// assert_eq!(*b, 24_u64);/// # Ok::<(), Error>(())/// ```pub type KBox<T> = Box<T, super::allocator::Kmalloc>; /// Type alias for [`Box`] with a [`Vmalloc`] allocator.////// # Examples////// ```/// let b = VBox::new(24_u64, GFP_KERNEL)?;////// assert_eq!(*b, 24_u64);/// # Ok::<(), Error>(())/// ```pub type VBox<T> = Box<T, super::allocator::Vmalloc>; /// Type alias for [`Box`] with a [`KVmalloc`] allocator.////// # Examples////// ```/// let b = KVBox::new(24_u64, GFP_KERNEL)?;////// assert_eq!(*b, 24_u64);/// # Ok::<(), Error>(())/// ```pub type KVBox<T> = Box<T, super::allocator::KVmalloc>; // SAFETY: All zeros is equivalent to `None` (option layout optimization guarantee:// <https://doc.rust-lang.org/stable/std/option/index.html#representation>).unsafe impl<T, A: Allocator> ZeroableOption for Box<T, A> {} // SAFETY: `Box` is `Send` if `T` is `Send` because the `Box` owns a `T`.unsafe impl<T, A> Send for Box<T, A>where    T: Send + ?Sized,    A: Allocator,{} // SAFETY: `Box` is `Sync` if `T` is `Sync` because the `Box` owns a `T`.unsafe impl<T, A> Sync for Box<T, A>where    T: Sync + ?Sized,    A: Allocator,{} impl<T, A> Box<T, A>where    T: ?Sized,    A: Allocator,{    /// Creates a new `Box<T, A>` from a raw pointer.    ///    /// # Safety    ///    /// For non-ZSTs, `raw` must point at an allocation allocated with `A` that is sufficiently    /// aligned for and holds a valid `T`. The caller passes ownership of the allocation to the    /// `Box`.    ///    /// For ZSTs, `raw` must be a dangling, well aligned pointer.    #[inline]    pub const unsafe fn from_raw(raw: *mut T) -> Self {        // INVARIANT: Validity of `raw` is guaranteed by the safety preconditions of this function.        // SAFETY: By the safety preconditions of this function, `raw` is not a NULL pointer.        Self(unsafe { NonNull::new_unchecked(raw) }, PhantomData)    }     /// Consumes the `Box<T, A>` and returns a raw pointer.    ///    /// This will not run the destructor of `T` and for non-ZSTs the allocation will stay alive    /// indefinitely. Use [`Box::from_raw`] to recover the [`Box`], drop the value and free the    /// allocation, if any.    ///    /// # Examples    ///    /// ```    /// let x = KBox::new(24, GFP_KERNEL)?;    /// let ptr = KBox::into_raw(x);    /// // SAFETY: `ptr` comes from a previous call to `KBox::into_raw`.    /// let x = unsafe { KBox::from_raw(ptr) };    ///    /// assert_eq!(*x, 24);    /// # Ok::<(), Error>(())    /// ```    #[inline]    pub fn into_raw(b: Self) -> *mut T {        ManuallyDrop::new(b).0.as_ptr()    }     /// Consumes and leaks the `Box<T, A>` and returns a mutable reference.    ///    /// See [`Box::into_raw`] for more details.    #[inline]    pub fn leak<'a>(b: Self) -> &'a mut T {        // SAFETY: `Box::into_raw` always returns a properly aligned and dereferenceable pointer        // which points to an initialized instance of `T`.        unsafe { &mut *Box::into_raw(b) }    }} impl<T, A> Box<MaybeUninit<T>, A>where    A: Allocator,{    /// Converts a `Box<MaybeUninit<T>, A>` to a `Box<T, A>`.    ///    /// It is undefined behavior to call this function while the value inside of `b` is not yet    /// fully initialized.    ///    /// # Safety    ///    /// Callers must ensure that the value inside of `b` is in an initialized state.    pub unsafe fn assume_init(self) -> Box<T, A> {        let raw = Self::into_raw(self);         // SAFETY: `raw` comes from a previous call to `Box::into_raw`. By the safety requirements        // of this function, the value inside the `Box` is in an initialized state. Hence, it is        // safe to reconstruct the `Box` as `Box<T, A>`.        unsafe { Box::from_raw(raw.cast()) }    }     /// Writes the value and converts to `Box<T, A>`.    pub fn write(mut self, value: T) -> Box<T, A> {        (*self).write(value);         // SAFETY: We've just initialized `b`'s value.        unsafe { self.assume_init() }    }} impl<T, A> Box<T, A>where    A: Allocator,{    /// Creates a new `Box<T, A>` and initializes its contents with `x`.    ///    /// New memory is allocated with `A`. The allocation may fail, in which case an error is    /// returned. For ZSTs no memory is allocated.    pub fn new(x: T, flags: Flags) -> Result<Self, AllocError> {        let b = Self::new_uninit(flags)?;        Ok(Box::write(b, x))    }     /// Creates a new `Box<T, A>` with uninitialized contents.    ///    /// New memory is allocated with `A`. The allocation may fail, in which case an error is    /// returned. For ZSTs no memory is allocated.    ///    /// # Examples    ///    /// ```    /// let b = KBox::<u64>::new_uninit(GFP_KERNEL)?;    /// let b = KBox::write(b, 24);    ///    /// assert_eq!(*b, 24_u64);    /// # Ok::<(), Error>(())    /// ```    pub fn new_uninit(flags: Flags) -> Result<Box<MaybeUninit<T>, A>, AllocError> {        let layout = Layout::new::<MaybeUninit<T>>();        let ptr = A::alloc(layout, flags)?;         // INVARIANT: `ptr` is either a dangling pointer or points to memory allocated with `A`,        // which is sufficient in size and alignment for storing a `T`.        Ok(Box(ptr.cast(), PhantomData))    }     /// Constructs a new `Pin<Box<T, A>>`. If `T` does not implement [`Unpin`], then `x` will be    /// pinned in memory and can't be moved.    #[inline]    pub fn pin(x: T, flags: Flags) -> Result<Pin<Box<T, A>>, AllocError>    where        A: 'static,    {        Ok(Self::new(x, flags)?.into())    }     /// Convert a [`Box<T,A>`] to a [`Pin<Box<T,A>>`]. If `T` does not implement    /// [`Unpin`], then `x` will be pinned in memory and can't be moved.    pub fn into_pin(this: Self) -> Pin<Self> {        this.into()    }     /// Forgets the contents (does not run the destructor), but keeps the allocation.    fn forget_contents(this: Self) -> Box<MaybeUninit<T>, A> {        let ptr = Self::into_raw(this);         // SAFETY: `ptr` is valid, because it came from `Box::into_raw`.        unsafe { Box::from_raw(ptr.cast()) }    }     /// Drops the contents, but keeps the allocation.    ///    /// # Examples    ///    /// ```    /// let value = KBox::new([0; 32], GFP_KERNEL)?;    /// assert_eq!(*value, [0; 32]);    /// let value = KBox::drop_contents(value);    /// // Now we can re-use `value`:    /// let value = KBox::write(value, [1; 32]);    /// assert_eq!(*value, [1; 32]);    /// # Ok::<(), Error>(())    /// ```    pub fn drop_contents(this: Self) -> Box<MaybeUninit<T>, A> {        let ptr = this.0.as_ptr();         // SAFETY: `ptr` is valid, because it came from `this`. After this call we never access the        // value stored in `this` again.        unsafe { core::ptr::drop_in_place(ptr) };         Self::forget_contents(this)    }     /// Moves the `Box`'s value out of the `Box` and consumes the `Box`.    pub fn into_inner(b: Self) -> T {        // SAFETY: By the type invariant `&*b` is valid for `read`.        let value = unsafe { core::ptr::read(&*b) };        let _ = Self::forget_contents(b);        value    }} impl<T, A> From<Box<T, A>> for Pin<Box<T, A>>where    T: ?Sized,    A: Allocator,{    /// Converts a `Box<T, A>` into a `Pin<Box<T, A>>`. If `T` does not implement [`Unpin`], then    /// `*b` will be pinned in memory and can't be moved.    ///    /// This moves `b` into `Pin` without moving `*b` or allocating and copying any memory.    fn from(b: Box<T, A>) -> Self {        // SAFETY: The value wrapped inside a `Pin<Box<T, A>>` cannot be moved or replaced as long        // as `T` does not implement `Unpin`.        unsafe { Pin::new_unchecked(b) }    }} impl<T, A> InPlaceWrite<T> for Box<MaybeUninit<T>, A>where    A: Allocator + 'static,{    type Initialized = Box<T, A>;     fn write_init<E>(mut self, init: impl Init<T, E>) -> Result<Self::Initialized, E> {        let slot = self.as_mut_ptr();        // SAFETY: When init errors/panics, slot will get deallocated but not dropped,        // slot is valid.        unsafe { init.__init(slot)? };        // SAFETY: All fields have been initialized.        Ok(unsafe { Box::assume_init(self) })    }     fn write_pin_init<E>(mut self, init: impl PinInit<T, E>) -> Result<Pin<Self::Initialized>, E> {        let slot = self.as_mut_ptr();        // SAFETY: When init errors/panics, slot will get deallocated but not dropped,        // slot is valid and will not be moved, because we pin it later.        unsafe { init.__pinned_init(slot)? };        // SAFETY: All fields have been initialized.        Ok(unsafe { Box::assume_init(self) }.into())    }} impl<T, A> InPlaceInit<T> for Box<T, A>where    A: Allocator + 'static,{    type PinnedSelf = Pin<Self>;     #[inline]    fn try_pin_init<E>(init: impl PinInit<T, E>, flags: Flags) -> Result<Pin<Self>, E>    where        E: From<AllocError>,    {        Box::<_, A>::new_uninit(flags)?.write_pin_init(init)    }     #[inline]    fn try_init<E>(init: impl Init<T, E>, flags: Flags) -> Result<Self, E>    where        E: From<AllocError>,    {        Box::<_, A>::new_uninit(flags)?.write_init(init)    }} // SAFETY: The `into_foreign` function returns a pointer that is well-aligned.unsafe impl<T: 'static, A> ForeignOwnable for Box<T, A>where    A: Allocator,{    type PointedTo = T;    type Borrowed<'a> = &'a T;    type BorrowedMut<'a> = &'a mut T;     fn into_foreign(self) -> *mut Self::PointedTo {        Box::into_raw(self)    }     unsafe fn from_foreign(ptr: *mut Self::PointedTo) -> Self {        // SAFETY: The safety requirements of this function ensure that `ptr` comes from a previous        // call to `Self::into_foreign`.        unsafe { Box::from_raw(ptr) }    }     unsafe fn borrow<'a>(ptr: *mut Self::PointedTo) -> &'a T {        // SAFETY: The safety requirements of this method ensure that the object remains alive and        // immutable for the duration of 'a.        unsafe { &*ptr }    }     unsafe fn borrow_mut<'a>(ptr: *mut Self::PointedTo) -> &'a mut T {        // SAFETY: The safety requirements of this method ensure that the pointer is valid and that        // nothing else will access the value for the duration of 'a.        unsafe { &mut *ptr }    }} // SAFETY: The `into_foreign` function returns a pointer that is well-aligned.unsafe impl<T: 'static, A> ForeignOwnable for Pin<Box<T, A>>where    A: Allocator,{    type PointedTo = T;    type Borrowed<'a> = Pin<&'a T>;    type BorrowedMut<'a> = Pin<&'a mut T>;     fn into_foreign(self) -> *mut Self::PointedTo {        // SAFETY: We are still treating the box as pinned.        Box::into_raw(unsafe { Pin::into_inner_unchecked(self) })    }     unsafe fn from_foreign(ptr: *mut Self::PointedTo) -> Self {        // SAFETY: The safety requirements of this function ensure that `ptr` comes from a previous        // call to `Self::into_foreign`.        unsafe { Pin::new_unchecked(Box::from_raw(ptr)) }    }     unsafe fn borrow<'a>(ptr: *mut Self::PointedTo) -> Pin<&'a T> {        // SAFETY: The safety requirements for this function ensure that the object is still alive,        // so it is safe to dereference the raw pointer.        // The safety requirements of `from_foreign` also ensure that the object remains alive for        // the lifetime of the returned value.        let r = unsafe { &*ptr };         // SAFETY: This pointer originates from a `Pin<Box<T>>`.        unsafe { Pin::new_unchecked(r) }    }     unsafe fn borrow_mut<'a>(ptr: *mut Self::PointedTo) -> Pin<&'a mut T> {        // SAFETY: The safety requirements for this function ensure that the object is still alive,        // so it is safe to dereference the raw pointer.        // The safety requirements of `from_foreign` also ensure that the object remains alive for        // the lifetime of the returned value.        let r = unsafe { &mut *ptr };         // SAFETY: This pointer originates from a `Pin<Box<T>>`.        unsafe { Pin::new_unchecked(r) }    }} impl<T, A> Deref for Box<T, A>where    T: ?Sized,    A: Allocator,{    type Target = T;     fn deref(&self) -> &T {        // SAFETY: `self.0` is always properly aligned, dereferenceable and points to an initialized        // instance of `T`.        unsafe { self.0.as_ref() }    }} impl<T, A> DerefMut for Box<T, A>where    T: ?Sized,    A: Allocator,{    fn deref_mut(&mut self) -> &mut T {        // SAFETY: `self.0` is always properly aligned, dereferenceable and points to an initialized        // instance of `T`.        unsafe { self.0.as_mut() }    }}

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