// SPDX-License-Identifier: GPL-2.0

//! Implementation of the kernel's memory allocation infrastructure.

#[cfg(not(any(test, testlib)))]
pub mod allocator;
pub mod kbox;
pub mod kvec;
pub mod layout;

#[cfg(any(test, testlib))]
pub mod allocator_test;

#[cfg(any(test, testlib))]
pub use self::allocator_test as allocator;

pub use self::kbox::Box;
pub use self::kbox::KBox;
pub use self::kbox::KVBox;
pub use self::kbox::VBox;

pub use self::kvec::IntoIter;
pub use self::kvec::KVVec;
pub use self::kvec::KVec;
pub use self::kvec::VVec;
pub use self::kvec::Vec;

/// Indicates an allocation error.
#[derive(Copy, Clone, PartialEq, Eq, Debug)]
pub struct AllocError;
use core::{alloc::Layout, ptr::NonNull};

/// Flags to be used when allocating memory.
///
/// They can be combined with the operators `|`, `&`, and `!`.
///
/// Values can be used from the [`flags`] module.
#[derive(Clone, Copy, PartialEq)]
pub struct Flags(u32);

impl Flags {
 /// Get the raw representation of this flag.
 pub(crate) fn as_raw(self) -> u32 {
 self.0
 }

 /// Check whether `flags` is contained in `self`.
 pub fn contains(self, flags: Flags) -> bool {
 (self & flags) == flags
 }
}

impl core::ops::BitOr for Flags {
 type Output = Self;
 fn bitor(self, rhs: Self) -> Self::Output {
 Self(self.0 | rhs.0)
 }
}

impl core::ops::BitAnd for Flags {
 type Output = Self;
 fn bitand(self, rhs: Self) -> Self::Output {
 Self(self.0 & rhs.0)
 }
}

impl core::ops::Not for Flags {
 type Output = Self;
 fn not(self) -> Self::Output {
 Self(!self.0)
 }
}

/// Allocation flags.
///
/// These are meant to be used in functions that can allocate memory.
pub mod flags {
 use super::Flags;

 /// Zeroes out the allocated memory.
 ///
 /// This is normally or'd with other flags.
 pub const __GFP_ZERO: Flags = Flags(bindings::__GFP_ZERO);

 /// Allow the allocation to be in high memory.
 ///
 /// Allocations in high memory may not be mapped into the kernel's address space, so this can't
 /// be used with `kmalloc` and other similar methods.
 ///
 /// This is normally or'd with other flags.
 pub const __GFP_HIGHMEM: Flags = Flags(bindings::__GFP_HIGHMEM);

 /// Users can not sleep and need the allocation to succeed.
 ///
 /// A lower watermark is applied to allow access to "atomic reserves". The current
 /// implementation doesn't support NMI and few other strict non-preemptive contexts (e.g.
 /// `raw_spin_lock`). The same applies to [`GFP_NOWAIT`].
 pub const GFP_ATOMIC: Flags = Flags(bindings::GFP_ATOMIC);

 /// Typical for kernel-internal allocations. The caller requires `ZONE_NORMAL` or a lower zone
 /// for direct access but can direct reclaim.
 pub const GFP_KERNEL: Flags = Flags(bindings::GFP_KERNEL);

 /// The same as [`GFP_KERNEL`], except the allocation is accounted to kmemcg.
 pub const GFP_KERNEL_ACCOUNT: Flags = Flags(bindings::GFP_KERNEL_ACCOUNT);

 /// For kernel allocations that should not stall for direct reclaim, start physical IO or
 /// use any filesystem callback. It is very likely to fail to allocate memory, even for very
 /// small allocations.
 pub const GFP_NOWAIT: Flags = Flags(bindings::GFP_NOWAIT);

 /// Suppresses allocation failure reports.
 ///
 /// This is normally or'd with other flags.
 pub const __GFP_NOWARN: Flags = Flags(bindings::__GFP_NOWARN);
}

/// The kernel's [`Allocator`] trait.
///
/// An implementation of [`Allocator`] can allocate, re-allocate and free memory buffers described
/// via [`Layout`].
///
/// [`Allocator`] is designed to be implemented as a ZST; [`Allocator`] functions do not operate on
/// an object instance.
///
/// In order to be able to support `#[derive(CoercePointee)]` later on, we need to avoid a design
/// that requires an `Allocator` to be instantiated, hence its functions must not contain any kind
/// of `self` parameter.
///
/// # Safety
///
/// - A memory allocation returned from an allocator must remain valid until it is explicitly freed.
///
/// - Any pointer to a valid memory allocation must be valid to be passed to any other [`Allocator`]
/// function of the same type.
///
/// - Implementers must ensure that all trait functions abide by the guarantees documented in the
/// `# Guarantees` sections.
pub unsafe trait Allocator {
 /// Allocate memory based on `layout` and `flags`.
 ///
 /// On success, returns a buffer represented as `NonNull<[u8]>` that satisfies the layout
 /// constraints (i.e. minimum size and alignment as specified by `layout`).
 ///
 /// This function is equivalent to `realloc` when called with `None`.
 ///
 /// # Guarantees
 ///
 /// When the return value is `Ok(ptr)`, then `ptr` is
 /// - valid for reads and writes for `layout.size()` bytes, until it is passed to
 /// [`Allocator::free`] or [`Allocator::realloc`],
 /// - aligned to `layout.align()`,
 ///
 /// Additionally, `Flags` are honored as documented in
 /// <https://docs.kernel.org/core-api/mm-api.html#mm-api-gfp-flags>.
 fn alloc(layout: Layout, flags: Flags) -> Result<NonNull<[u8]>, AllocError> {
 // SAFETY: Passing `None` to `realloc` is valid by its safety requirements and asks for a
 // new memory allocation.
 unsafe { Self::realloc(None, layout, Layout::new::<()>(), flags) }
 }

 /// Re-allocate an existing memory allocation to satisfy the requested `layout`.
 ///
 /// If the requested size is zero, `realloc` behaves equivalent to `free`.
 ///
 /// If the requested size is larger than the size of the existing allocation, a successful call
 /// to `realloc` guarantees that the new or grown buffer has at least `Layout::size` bytes, but
 /// may also be larger.
 ///
 /// If the requested size is smaller than the size of the existing allocation, `realloc` may or
 /// may not shrink the buffer; this is implementation specific to the allocator.
 ///
 /// On allocation failure, the existing buffer, if any, remains valid.
 ///
 /// The buffer is represented as `NonNull<[u8]>`.
 ///
 /// # Safety
 ///
 /// - If `ptr == Some(p)`, then `p` must point to an existing and valid memory allocation
 /// created by this [`Allocator`]; if `old_layout` is zero-sized `p` does not need to be a
 /// pointer returned by this [`Allocator`].
 /// - `ptr` is allowed to be `None`; in this case a new memory allocation is created and
 /// `old_layout` is ignored.
 /// - `old_layout` must match the `Layout` the allocation has been created with.
 ///
 /// # Guarantees
 ///
 /// This function has the same guarantees as [`Allocator::alloc`]. When `ptr == Some(p)`, then
 /// it additionally guarantees that:
 /// - the contents of the memory pointed to by `p` are preserved up to the lesser of the new
 /// and old size, i.e. `ret_ptr[0..min(layout.size(), old_layout.size())] ==
 /// p[0..min(layout.size(), old_layout.size())]`.
 /// - when the return value is `Err(AllocError)`, then `ptr` is still valid.
 unsafe fn realloc(
 ptr: Option<NonNull<u8>>,
 layout: Layout,
 old_layout: Layout,
 flags: Flags,
 ) -> Result<NonNull<[u8]>, AllocError>;

 /// Free an existing memory allocation.
 ///
 /// # Safety
 ///
 /// - `ptr` must point to an existing and valid memory allocation created by this [`Allocator`];
 /// if `old_layout` is zero-sized `p` does not need to be a pointer returned by this
 /// [`Allocator`].
 /// - `layout` must match the `Layout` the allocation has been created with.
 /// - The memory allocation at `ptr` must never again be read from or written to.
 unsafe fn free(ptr: NonNull<u8>, layout: Layout) {
 // SAFETY: The caller guarantees that `ptr` points at a valid allocation created by this
 // allocator. We are passing a `Layout` with the smallest possible alignment, so it is
 // smaller than or equal to the alignment previously used with this allocation.
 let _ = unsafe { Self::realloc(Some(ptr), Layout::new::<()>(), layout, Flags(0)) };
 }
}

/// Returns a properly aligned dangling pointer from the given `layout`.
pub(crate) fn dangling_from_layout(layout: Layout) -> NonNull<u8> {
 let ptr = layout.align() as *mut u8;

 // SAFETY: `layout.align()` (and hence `ptr`) is guaranteed to be non-zero.
 unsafe { NonNull::new_unchecked(ptr) }
}