无法从伪终端读取

Question

我编写了一个高级包装器和命令集合，它使用RProc / RPMsg接口与微处理器通信，以便尽可能地测试我为它编写的单元测试使用Linux伪终端来代替'真正的'界面。

我的测试不起作用。 我最终将测试简化到了不包含我的代码痕迹的地步 - 它仍然不起作用：

BOOST_AUTO_TEST_CASE(constructor)
{
    const auto master_pty = ::posix_openpt(O_RDWR);
    BOOST_REQUIRE(master_pty != -1);
    BOOST_REQUIRE(::grantpt(master_pty) != -1);
    BOOST_REQUIRE(::unlockpt(master_pty) != -1);

    const auto slave_pty_name = ::ptsname(master_pty);
    const auto slave_pty = ::open(slave_pty_name, O_RDWR);
    BOOST_REQUIRE(slave_pty != -1);

    const auto in_data = std::array<std::uint8_t, 4>{1, 2, 3, 4};
    const auto bytes_written = ::write(master_pty, in_data.data(), in_data.size());
    if (bytes_written < 0) {
        BOOST_FAIL("Failed to write: " << errno);
    }
    BOOST_REQUIRE_EQUAL(in_data.size(), bytes_written);

    auto out_data = std::array<std::uint8_t, in_data.size()>{};
    const auto bytes_read = ::read(slave_pty, out_data.data(), out_data.size());
    BOOST_CHECK_EQUAL(bytes_read, bytes_written);
    if (bytes_read < 0) {
        BOOST_FAIL("::read failed: " << errno);
    }

    ::close(slave_pty);
    ::close(master_pty);
}

其输出是：

*** 1 failure is detected in the test module "cmPTP Test Suite"
# cmPTP-manager-test -l all --run_test=comms_rproc_interface/constructor
Running 1 test case...
Entering test module "cmPTP Test Suite"
interface_test.cpp(17): Entering test suite "comms_rproc_interface"
interface_test.cpp(19): Entering test case "constructor"
interface_test.cpp(23): info: check master_pty != -1 has passed
interface_test.cpp(24): info: check grantpt(master_pty) != -1 has passed
interface_test.cpp(25): info: check unlockpt(master_pty) != -1 has passed
interface_test.cpp(32): info: check slave_pty != -1 has passed
interface_test.cpp(72): info: check in_data.size() == bytes_written has passed
interface_test.cpp(77): error: in "comms_rproc_interface/constructor": check bytes_read == bytes_written has failed [0 != 4]
interface_test.cpp(19): Leaving test case "constructor"; testing time: 15282us
interface_test.cpp(17): Leaving test suite "comms_rproc_interface"; testing time: 15931us
Leaving test module "cmPTP Test Suite"; testing time: 16879us

*** 1 failure is detected in the test module "cmPTP Test Suite"

我可以把我的4个字节编写得很好，但是从属端没有任何东西存在。 为什么？

Answer 1

这是因为我忘记了我正在创建一个伪终端而不是一个串行设备。 PTY将我的输入值视为ASCII（这可能会让它有点吓人），并且在刷新之前等待换行 - 所以@ starturtle关于刷新的评论是正确的，只是没有以'正常'文件写入方式。

这个简洁的SSCCE展示了我应该如何做到这一点：

#include <unistd.h>
#include <pty.h>

#include <array>
#include <iostream>

int main()
{
    // Make the PTY 'raw' to disable traditional terminal-like
    // behaviour
    struct termios ts;
    cfmakeraw(&ts);

    auto master_pty = -1;
    auto slave_pty  = -1;
    if (::openpty(&master_pty, &slave_pty, nullptr, &ts, nullptr) < 0) {
        std::cerr << "Cannot create PTY: " << errno << std::endl;
        return EXIT_FAILURE;
    }

    const auto in_data = std::array<std::uint8_t, 5>{1, 2, 3, 4, 5};
    const auto bytes_written = ::write(master_pty, in_data.data(), in_data.size());
    if (bytes_written < 0) {
        std::cerr << "Failed to write: " << errno << std::endl;
        return EXIT_FAILURE;
    }

    auto out_data = std::array<std::uint8_t, in_data.size()>{};
    out_data.fill(0);

    const auto bytes_read = ::read(slave_pty, out_data.data(), out_data.size());
    if (bytes_read < 0) {
        std::cerr << "::read failed: " << errno << std::endl;
        return EXIT_FAILURE;
    }

    for (auto&& c : out_data) {
        std::cout << static_cast<int>(c);
    }
    std::cout << std::endl;

    ::close(slave_pty);
    ::close(master_pty);
}