io_buffer.hpp

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#pragma once
 
#include <cstddef>
#include <cstdint>
#include <span>
 
#include "expected.hpp"
 
using VirtToPhysFunc = auto (*)(uintptr_t virt) -> uintptr_t;
 
[[nodiscard]] inline auto IdentityVirtToPhys(uintptr_t virt) -> uintptr_t {
  return virt;
}
 
struct DmaRegion {
  void* virt{nullptr};
  uintptr_t phys{0};
  size_t size{0};
 
  [[nodiscard]] auto IsValid() const -> bool {
    return virt != nullptr && size > 0;
  }
 
  [[nodiscard]] auto Data() const -> uint8_t* {
    return static_cast<uint8_t*>(virt);
  }
 
  [[nodiscard]] auto SubRegion(size_t offset, size_t len) const
      -> Expected<DmaRegion> {
    if (offset > size || len > size - offset) {
      return std::unexpected(Error{ErrorCode::kInvalidArgument});
    }
    return DmaRegion{
        .virt = static_cast<uint8_t*>(virt) + offset,
        .phys = phys + offset,
        .size = len,
    };
  }
};
 
class IoBuffer {
 public:
  static constexpr size_t kDefaultAlignment = 4096;
 
  [[nodiscard]] auto GetBuffer() const -> std::span<const uint8_t>;
 
  [[nodiscard]] auto GetBuffer() -> std::span<uint8_t>;
 
  [[nodiscard]] auto IsValid() const -> bool;
 
  [[nodiscard]] auto ToDmaRegion(VirtToPhysFunc v2p = IdentityVirtToPhys) const
      -> DmaRegion;
 
  IoBuffer() = default;
 
  explicit IoBuffer(size_t size, size_t alignment = kDefaultAlignment);
 
  ~IoBuffer();
 
  IoBuffer(const IoBuffer&) = delete;
  auto operator=(const IoBuffer&) -> IoBuffer& = delete;
 
  IoBuffer(IoBuffer&& other);
  auto operator=(IoBuffer&& other) noexcept -> IoBuffer&;
 
 private:
  uint8_t* data_{nullptr};
  size_t size_{0};
};