Class copy_file_data_sendfile

src/operations.cpp:820–872

#if defined(BOOST_FILESYSTEM_USE_SENDFILE)

struct copy_file_data_sendfile
{
    //! copy_file implementation that uses sendfile loop. Requires sendfile to support file descriptors.
    static int impl(int infile, int outfile, uintmax_t size, std::size_t blksize)
    {
        // sendfile will not send more than this amount of data in one call
        BOOST_CONSTEXPR_OR_CONST std::size_t max_batch_size = 0x7ffff000u;
        uintmax_t offset = 0u;
        while (offset < size)
        {
            uintmax_t size_left = size - offset;
            std::size_t size_to_copy = max_batch_size;
            if (size_left < static_cast< uintmax_t >(max_batch_size))
                size_to_copy = static_cast< std::size_t >(size_left);
            ssize_t sz = ::sendfile(outfile, infile, nullptr, size_to_copy);
            if (BOOST_LIKELY(sz > 0))
            {
                offset += sz;
            }
            else if (sz < 0)
            {
                int err = errno;
                if (err == EINTR)
                    continue;

                if (offset == 0u)
                {
                    // sendfile may fail with EINVAL if the underlying filesystem does not support it
                    if (err == EINVAL)
                    {
                    fallback_to_read_write:
                        return copy_file_data_read_write(infile, outfile, size, blksize);
                    }

                    if (err == ENOSYS)
                    {
                        filesystem::detail::atomic_store_relaxed(copy_file_data, &copy_file_data_read_write);
                        goto fallback_to_read_write;
                    }
                }

                return err;
            }
            else
            {
                // EOF: the input file was truncated while copying was in progress
                break;
            }
        }

        return 0;
    }
};

#endif // defined(BOOST_FILESYSTEM_USE_SENDFILE)