From 41f41393067080223422122b8ae1a0dcfe9e5f8f Mon Sep 17 00:00:00 2001
From: Thiago Macieira <thiago.macieira@intel.com>
Date: Thu, 8 Jun 2023 21:20:57 -0700
Subject: [PATCH] QEventDispatcherUNIX: remove the fallback to pipes on eventfd
 systems

Linux has had it since 2.6.23, which is positively ancient from our
perspective. No one runs Qt on systems anywhere near that old (I'd be
amazed if anyone managed on CentOS / RHEL 7, which carries Linux 3.10).
And we don't deal with ENOSYS on FreeBSD either.

The removal is accomplished by dead code elimination: it's still
compiled on Linux and FreeBSD.

Drive-by
 - use NSDMI in QThreadPipe
 - remove EINTR_LOOP for eventfd_write(3): it can't be interrupted

Change-Id: I63b988479db546dabffcfffd1766e2c7acc6da46
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>
---
 src/corelib/kernel/qeventdispatcher_unix.cpp | 33 +++++++-------------
 src/corelib/kernel/qeventdispatcher_unix_p.h |  8 ++---
 2 files changed, 15 insertions(+), 26 deletions(-)

diff --git a/src/corelib/kernel/qeventdispatcher_unix.cpp b/src/corelib/kernel/qeventdispatcher_unix.cpp
index 7b965fde3d4..dc87a9cd639 100644
--- a/src/corelib/kernel/qeventdispatcher_unix.cpp
+++ b/src/corelib/kernel/qeventdispatcher_unix.cpp
@@ -45,11 +45,6 @@ static const char *socketType(QSocketNotifier::Type type)
 
 QThreadPipe::QThreadPipe()
 {
-    fds[0] = -1;
-    fds[1] = -1;
-#if defined(Q_OS_VXWORKS)
-    name[0] = '\0';
-#endif
 }
 
 QThreadPipe::~QThreadPipe()
@@ -57,7 +52,7 @@ QThreadPipe::~QThreadPipe()
     if (fds[0] >= 0)
         close(fds[0]);
 
-    if (fds[1] >= 0)
+    if (!QT_CONFIG(eventfd) && fds[1] >= 0)
         close(fds[1]);
 
 #if defined(Q_OS_VXWORKS)
@@ -106,11 +101,13 @@ bool QThreadPipe::init()
     initThreadPipeFD(fds[0]);
     fds[1] = fds[0];
 #else
+    int ret;
 #  if QT_CONFIG(eventfd)
-    if ((fds[0] = eventfd(0, EFD_NONBLOCK | EFD_CLOEXEC)) >= 0)
-        return true;
+    ret = fds[0] = eventfd(0, EFD_NONBLOCK | EFD_CLOEXEC);
 #  endif
-    if (qt_safe_pipe(fds, O_NONBLOCK) == -1) {
+    if (!QT_CONFIG(eventfd))
+        ret = qt_safe_pipe(fds, O_NONBLOCK);
+    if (ret == -1) {
         perror("QThreadPipe: Unable to create pipe");
         return false;
     }
@@ -128,13 +125,8 @@ void QThreadPipe::wakeUp()
 {
     if (wakeUps.testAndSetAcquire(0, 1)) {
 #if QT_CONFIG(eventfd)
-        if (fds[1] == -1) {
-            // eventfd
-            eventfd_t value = 1;
-            int ret;
-            EINTR_LOOP(ret, eventfd_write(fds[0], value));
-            return;
-        }
+        eventfd_write(fds[0], 1);
+        return;
 #endif
         char c = 0;
         qt_safe_write(fds[1], &c, 1);
@@ -156,13 +148,10 @@ int QThreadPipe::check(const pollfd &pfd)
         ::ioctl(fds[0], FIOFLUSH, 0);
 #else
 #  if QT_CONFIG(eventfd)
-        if (fds[1] == -1) {
-            // eventfd
-            eventfd_t value;
-            eventfd_read(fds[0], &value);
-        } else
+        eventfd_t value;
+        eventfd_read(fds[0], &value);
 #  endif
-        {
+        if (!QT_CONFIG(eventfd)) {
             while (::read(fds[0], c, sizeof(c)) > 0) {}
         }
 #endif
diff --git a/src/corelib/kernel/qeventdispatcher_unix_p.h b/src/corelib/kernel/qeventdispatcher_unix_p.h
index 4e9a360f3e2..2479cd1e630 100644
--- a/src/corelib/kernel/qeventdispatcher_unix_p.h
+++ b/src/corelib/kernel/qeventdispatcher_unix_p.h
@@ -51,13 +51,13 @@ struct QThreadPipe
     int check(const pollfd &pfd);
 
     // note for eventfd(7) support:
-    // if fds[1] is -1, then eventfd(7) is in use and is stored in fds[0]
-    int fds[2];
+    // fds[0] stores the eventfd, fds[1] is unused
+    int fds[2] = { -1, -1 };
     QAtomicInt wakeUps;
 
 #if defined(Q_OS_VXWORKS)
-    static const int len_name = 20;
-    char name[len_name];
+    static constexpr int len_name = 20;
+    char name[len_name] = {};
 #endif
 };