Method Read

src/leveldb/util/env_posix.cc:173–198

  }

  Status Read(uint64_t offset, size_t n, Slice* result,
              char* scratch) const override {
    int fd = fd_;
    if (!has_permanent_fd_) {
      fd = ::open(filename_.c_str(), O_RDONLY | kOpenBaseFlags);
      if (fd < 0) {
        return PosixError(filename_, errno);
      }
    }

    assert(fd != -1);

    Status status;
    ssize_t read_size = ::pread(fd, scratch, n, static_cast<off_t>(offset));
    *result = Slice(scratch, (read_size < 0) ? 0 : read_size);
    if (read_size < 0) {
      // An error: return a non-ok status.
      status = PosixError(filename_, errno);
    }
    if (!has_permanent_fd_) {
      // Close the temporary file descriptor opened earlier.
      assert(fd != fd_);
      ::close(fd);
    }
    return status;
  }

  virtual std::string GetName() const override { return filename_; }