zircon/kernel/phys/include/phys/allocation.h

// Copyright 2021 The Fuchsia Authors
//
// Use of this source code is governed by a MIT-style
// license that can be found in the LICENSE file or at
// https://opensource.org/licenses/MIT

#ifndef ZIRCON_KERNEL_PHYS_INCLUDE_PHYS_ALLOCATION_H_
#define ZIRCON_KERNEL_PHYS_INCLUDE_PHYS_ALLOCATION_H_

#include <lib/fitx/result.h>

#include <fbl/alloc_checker.h>
#include <ktl/algorithm.h>
#include <ktl/byte.h>
#include <ktl/move.h>
#include <ktl/span.h>
#include <ktl/string_view.h>

namespace memalloc {

// Forward-declared; declared in <lib/memalloc/range.h>.
enum class Type : uint64_t;

// Forward-declared; declared in <lib/memalloc/pool.h>.
class Pool;

}  // namespace memalloc

// This object represents one memory allocation, and owns that allocation so
// destroying this object frees the allocation.  It acts as a smart pointer
// that also knows the size so it can deliver a raw pointer or a span<byte>.
class Allocation {
 public:
  // A default-constructed object is like a null pointer.
  // Allocation::New() must be called to create a non-null Allocation.
  Allocation() = default;

  Allocation(const Allocation&) = delete;

  Allocation(Allocation&& other) noexcept { *this = ktl::move(other); }

  Allocation& operator=(const Allocation&) = delete;

  Allocation& operator=(Allocation&& other) noexcept {
    ktl::swap(data_, other.data_);
    return *this;
  }

  ~Allocation() { reset(); }

  auto data() const { return data_; }

  size_t size_bytes() const { return data_.size(); }

  auto get() const { return data_.data(); }

  void reset();

  // This returns the span like data() but transfers ownership like a move.
  [[nodiscard]] auto release() {
    auto result = data_;
    data_ = {};
    return result;
  }

  explicit operator bool() const { return !data_.empty(); }

  // If allocation fails, operator bool will return false later.
  // The AllocChecker must be checked after construction, too.
  static Allocation New(fbl::AllocChecker& ac, memalloc::Type type, size_t size,
                        size_t alignment = __STDCPP_DEFAULT_NEW_ALIGNMENT__);

  // Get the memalloc::Pool instance used to construct Allocation objects.
  // Every call returns the same object, but the first may initialize it.  Note
  // separate #include <lib/memalloc/pool.h> is necessary to use the instance.
  [[gnu::const]] static memalloc::Pool& GetPool();

 private:
  ktl::span<ktl::byte> data_;
};

#endif  // ZIRCON_KERNEL_PHYS_INCLUDE_PHYS_ALLOCATION_H_