QProcess/Linux: add a flag to re-enable the vfork()-like semantics

Commit 29b2fe40dc778ec73da7e5643fcfd8979d8ecebc disabled it by reverting
commit d6bf71123d3ef073f25610345cb5dc920e4fb783. We now add the promised
flag to opt-in. The flag is added to all Unix systems, but it really
only applies to Linux right now.

No ChangeLog because the whole UnixProcessParameters structure is new
and has its own changelog.

Task-number: QTBUG-104493
Task-number: QTBUG-111243
Task-number: QTBUG-111964
Change-Id: Icfe44ecf285a480fafe4fffd174d4effd3382495
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>
Reviewed-by: Paul Wicking <paul.wicking@qt.io>
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@gmx.de>

1 files changed, 16 insertions, 2 deletions

diff --git a/tests/auto/corelib/io/qprocess/tst_qprocess.cpp b/tests/auto/corelib/io/qprocess/tst_qprocess.cpp
index 069440c49b..540df04f73 100644
--- a/tests/auto/corelib/io/qprocess/tst_qprocess.cpp
+++ b/tests/auto/corelib/io/qprocess/tst_qprocess.cpp
@@ -21,6 +21,7 @@
 #include <qplatformdefs.h>
 #ifdef Q_OS_UNIX
 #  include <private/qcore_unix_p.h>
+#  include <sys/wait.h>
 #endif
 
 #include <QtTest/private/qemulationdetector_p.h>
@@ -157,6 +158,7 @@ protected slots:
 private:
     qint64 bytesAvailable;
     QTemporaryDir m_temporaryDir;
+    bool haveWorkingVFork = false;
 };
 
 void tst_QProcess::initTestCase()
@@ -168,6 +170,12 @@ void tst_QProcess::initTestCase()
     // chdir to our testdata path and execute helper apps relative to that.
     QString testdata_dir = QFileInfo(QFINDTESTDATA("testProcessNormal")).absolutePath();
     QVERIFY2(QDir::setCurrent(testdata_dir), qPrintable("Could not chdir to " + testdata_dir));
+
+#if defined(Q_OS_LINUX) && QT_CONFIG(forkfd_pidfd)
+    // see detect_clone_pidfd_support() in forkfd_linux.c for explanation
+    waitid(/*P_PIDFD*/ idtype_t(3), INT_MAX, NULL, WEXITED|WNOHANG);
+    haveWorkingVFork = (errno == EBADF);
+#endif
 }
 
 void tst_QProcess::cleanupTestCase()
@@ -1515,6 +1523,7 @@ void tst_QProcess::unixProcessParametersAndChildModifier()
     static constexpr char message[] = "Message from the handler function\n";
     static_assert(std::char_traits<char>::length(message) <= PIPE_BUF);
     QProcess process;
+    QAtomicInt vforkControl;
     int pipes[2];
 
     QVERIFY2(pipe(pipes) == 0, qPrintable(qt_error_string()));
@@ -1523,10 +1532,12 @@ void tst_QProcess::unixProcessParametersAndChildModifier()
         auto pipeGuard1 = qScopeGuard([=] { close(pipes[1]); });
 
         // verify that our modifier runs before the parameters are applied
-        process.setChildProcessModifier([=] {
+        process.setChildProcessModifier([=, &vforkControl] {
             write(pipes[1], message, strlen(message));
+            vforkControl.storeRelaxed(1);
         });
-        auto flags = QProcess::UnixProcessFlag::CloseNonStandardFileDescriptors;
+        auto flags = QProcess::UnixProcessFlag::CloseNonStandardFileDescriptors |
+                QProcess::UnixProcessFlag::UseVFork;
         process.setUnixProcessParameters({ flags });
         process.setProgram("testUnixProcessParameters/testUnixProcessParameters");
         process.setArguments({ "std-file-descriptors", QString::number(pipes[1]) });
@@ -1542,6 +1553,9 @@ void tst_QProcess::unixProcessParametersAndChildModifier()
     int r = read(pipes[0], buf, sizeof(buf));
     QVERIFY2(r >= 0, qPrintable(qt_error_string()));
     QCOMPARE(QByteArrayView(buf, r), message);
+
+    if (haveWorkingVFork)
+        QVERIFY2(vforkControl.loadRelaxed(), "QProcess doesn't appear to have used vfork()");
 }
 #endif