無法從僞終端讀取

我寫了一個高級包裝和命令集合，它使用RProc/RPMsg接口與微處理器進行通信，爲了儘可能多地測試我爲它編寫了單元測試一個Linux僞終端代替'真實'的界面。無法從僞終端讀取

我的測試沒有奏效。我最終簡化了測試，它沒有包含我的代碼痕跡點 - 它仍然不能正常工作：

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); 
}

它的輸出是：

*** 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"

我可以寫我的4字節好，但是從來沒有任何東西存在。爲什麼？

來源

2017-05-06 cmannett85

這看起來並不像讀出的實際上是失敗了，但它並沒有檢索字節。寫入緩衝區是否已被刷新？ – starturtle

@starturtle應該有：「POSIX要求在write（）返回後可以證明發生的讀（2）返回新數據。注意並非所有的文件系統都符合POSIX標準。」我當然認爲Linux/EXT4符合POSIX標準......我如何強制刷新？ – cmannett85

@starturtle其實它只是在我身上發現PTS是_two_文件描述符，所以上述不適用。 – cmannett85

這是因爲我忘了我正在創建一個僞終端而不是一個串行設備。 PTY正在將我的輸入值視爲ASCII（可能會使它變得有點嚇人），並且在刷新之前正在等待線返回 - 因此@starturtle關於刷新的評論是正確的，而不是以「正常」文件寫入方式。

這繁瑣SSCCE顯示我應該怎麼做它：

#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); 
}

來源

2017-05-07 10:12:55 cmannett85

無法從僞終端讀取

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