Avoid potential data races caused by qt_ntfs_permission_lookup

qt_ntfs_permission_lookup is a global, non-atomic variable which
could cause problems in case of multiple threads. Introduce a
new atomic variable to handle permission lookups but instead of
manual incrementation/decrementation, implement a class to manage
the variable.

Since the atomic variable is not directly available to the user,
implement helper functions to increase/decrease/check the status
of the variable.

Task-number: QTBUG-105804
Change-Id: If6cbcdd653c7f50ad9853a5c309e24fdeb520788
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Marc Mutz <marc.mutz@qt.io>

1 files changed, 13 insertions, 0 deletions

diff --git a/src/corelib/io/qfileinfo.cpp b/src/corelib/io/qfileinfo.cpp
index 49573347ca..5c9ae5df70 100644
--- a/src/corelib/io/qfileinfo.cpp
+++ b/src/corelib/io/qfileinfo.cpp
@@ -278,6 +278,19 @@ QDateTime &QFileInfoPrivate::getFileTime(QAbstractFileEngine::FileTime request)
     threads other than the main thread have started or after every thread
     other than the main thread has ended.
 
+    \note From Qt 6.6 the variable \c qt_ntfs_permission_lookup is
+    deprecated. Please use the following alternatives.
+
+    The safe and easy way to manage permission checks is to use the RAII class
+    \c QNtfsPermissionCheckGuard.
+
+    \snippet ntfsp.cpp raii
+
+    If you need more fine-grained control, it is possible to manage the permission
+    with the following functions instead:
+
+    \snippet ntfsp.cpp free-funcs
+
     \section1 Performance Considerations
 
     Some of QFileInfo's functions query the file system, but for