text: /*
   * Copyright (C) 2018 The Android Open Source Project
   *
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   *
   *      http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  
  #include "android-base/mapped_file.h"
  
  #include <errno.h>
  
  namespace android {
  namespace base {
  
  static off64_t InitPageSize() {
  #if defined(_WIN32)
    SYSTEM_INFO si;
    GetSystemInfo(&si);
    return si.dwAllocationGranularity;
  #else
    return sysconf(_SC_PAGE_SIZE);
  #endif
  }
  
  std::unique_ptr<MappedFile> MappedFile::FromFd(int fd, off64_t offset, size_t length, int prot) {
    static off64_t page_size = InitPageSize();
    size_t slop = offset % page_size;
    off64_t file_offset = offset - slop;
    off64_t file_length = length + slop;
  
  #if defined(_WIN32)
    HANDLE handle =
        CreateFileMapping(reinterpret_cast<HANDLE>(_get_osfhandle(fd)), nullptr,
                          (prot & PROT_WRITE) ? PAGE_READWRITE : PAGE_READONLY, 0, 0, nullptr);
    if (handle == nullptr) {
      // http://b/119818070 "app crashes when reading asset of zero length".
      // Return a MappedFile that's only valid for reading the size.
      if (length == 0) {
        return std::unique_ptr<MappedFile>(new MappedFile{nullptr, 0, 0, nullptr});
      }
      return nullptr;
    }
    void* base = MapViewOfFile(handle, (prot & PROT_WRITE) ? FILE_MAP_ALL_ACCESS : FILE_MAP_READ, 0,
                               file_offset, file_length);
    if (base == nullptr) {
      CloseHandle(handle);
      return nullptr;
    }
    return std::unique_ptr<MappedFile>(
        new MappedFile{static_cast<char*>(base), length, slop, handle});
  #else
    void* base = mmap(nullptr, file_length, prot, MAP_SHARED, fd, file_offset);
    if (base == MAP_FAILED) {
      // http://b/119818070 "app crashes when reading asset of zero length".
      // mmap fails with EINVAL for a zero length region.
      if (errno == EINVAL && length == 0) {
        return std::unique_ptr<MappedFile>(new MappedFile{nullptr, 0, 0});
      }
      return nullptr;
    }
    return std::unique_ptr<MappedFile>(new MappedFile{static_cast<char*>(base), length, slop});
  #endif
  }
  
  MappedFile::~MappedFile() {
  #if defined(_WIN32)
    if (base_ != nullptr) UnmapViewOfFile(base_);
    if (handle_ != nullptr) CloseHandle(handle_);
  #else
    if (base_ != nullptr) munmap(base_, size_ + offset_);
  #endif
  
    base_ = nullptr;
    offset_ = size_ = 0;
  }
  
  }  // namespace base
  }  // namespace android
  