From cc0306a107d3ec60fadf08c66ab260970826564a Mon Sep 17 00:00:00 2001
From: Gong Heng <gongheng@uniontech.com>
Date: Thu, 18 Mar 2021 16:53:11 +0800
Subject: [PATCH 008/147] =?UTF-8?q?fix:=20Optimize=20the=20performance=20o?=
 =?UTF-8?q?f=20the=20inotify=20file=20system=20monitoring=20program?=
 =?UTF-8?q?=E3=80=82?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

When the ioctl() functions is executed correctly, the value of buffSize may be 0.
In this situation, there is no need to execute the following code.
This modification can solve two benefits:
1. The readFromInotify function runs frequently, and this modification can improve the
efficiency of the program.
2. When the buffSize is equal to 0, "read(inotifyFd, buffer.data(), buffSize)" function will
be stuck.(I have encountered this kind of problem)

Pick-to: 5.15 6.0 6.1
Change-Id: I9f85491ec91e336b4a1bec5c99b911835c5c06a5
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>
(cherry picked from commit bb8fc324d16278c27a211093fb47bafcc4fe7874)
---
 src/corelib/io/qfilesystemwatcher_inotify.cpp | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/src/corelib/io/qfilesystemwatcher_inotify.cpp b/src/corelib/io/qfilesystemwatcher_inotify.cpp
index 94d9d06bcb..27e0b13b0b 100644
--- a/src/corelib/io/qfilesystemwatcher_inotify.cpp
+++ b/src/corelib/io/qfilesystemwatcher_inotify.cpp
@@ -366,7 +366,9 @@ void QInotifyFileSystemWatcherEngine::readFromInotify()
     // qDebug("QInotifyFileSystemWatcherEngine::readFromInotify");
 
     int buffSize = 0;
-    ioctl(inotifyFd, FIONREAD, (char *) &buffSize);
+    if (ioctl(inotifyFd, FIONREAD, (char *) &buffSize) == -1 || buffSize == 0)
+        return;
+
     QVarLengthArray<char, 4096> buffer(buffSize);
     buffSize = read(inotifyFd, buffer.data(), buffSize);
     char *at = buffer.data();
-- 
2.40.1