Windows/QSaveFile: Fix locking issues on Dropbox drives

Add a flag to QTemporaryFileEngine causing the file to be opened in
non-shared mode, preventing renaming failures caused by the Dropbox
driver accessing it.

Task-number: QTBUG-57299
Change-Id: Id7afc3559fd15784d4166efbbd057d592b5e0ab2
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@qt.io>
Reviewed-by: Oliver Wolff <oliver.wolff@qt.io>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
(cherry picked from commit fe5edcee602f0ab2912bbdd1a21f4309ed7dbfd6)
Reviewed-by: Frederik Gladhorn <frederik.gladhorn@qt.io>
Reviewed-by: Kai Pastor <dg0yt@darc.de>

3 files changed, 13 insertions, 5 deletions

diff --git a/src/corelib/io/qsavefile.cpp b/src/corelib/io/qsavefile.cpp
index 3f45ca5f91..aaf3d1f5fb 100644
--- a/src/corelib/io/qsavefile.cpp
+++ b/src/corelib/io/qsavefile.cpp
@@ -231,7 +231,7 @@ bool QSaveFile::open(OpenMode mode)
             d->finalFileName = existingFile.filePath();
     }
 
-    d->fileEngine = new QTemporaryFileEngine;
+    d->fileEngine = new QTemporaryFileEngine(QTemporaryFileEngine::Win32NonShared);
     // if the target file exists, we'll copy its permissions below,
     // but until then, let's ensure the temporary file is not accessible
     // to a third party
diff --git a/src/corelib/io/qtemporaryfile.cpp b/src/corelib/io/qtemporaryfile.cpp
index 8a99873fee..4712e65a41 100644
--- a/src/corelib/io/qtemporaryfile.cpp
+++ b/src/corelib/io/qtemporaryfile.cpp
@@ -117,7 +117,7 @@ typedef int NativeFileHandle;
 */
 static bool createFileFromTemplate(NativeFileHandle &file,
         QFileSystemEntry::NativePath &path, size_t pos, size_t length, quint32 mode,
-        QSystemError &error)
+        int flags, QSystemError &error)
 {
     Q_ASSERT(length != 0);
     Q_ASSERT(pos < size_t(path.length()));
@@ -151,16 +151,18 @@ static bool createFileFromTemplate(NativeFileHandle &file,
         // Atomically create file and obtain handle
 #if defined(Q_OS_WIN)
         Q_UNUSED(mode);
+        const DWORD shareMode = (flags & QTemporaryFileEngine::Win32NonShared)
+                                ? 0u : (FILE_SHARE_READ | FILE_SHARE_WRITE);
 
 #  ifndef Q_OS_WINRT
         file = CreateFile((const wchar_t *)path.constData(),
                 GENERIC_READ | GENERIC_WRITE,
-                FILE_SHARE_READ | FILE_SHARE_WRITE, NULL, CREATE_NEW,
+                shareMode, NULL, CREATE_NEW,
                 FILE_ATTRIBUTE_NORMAL, NULL);
 #  else // !Q_OS_WINRT
         file = CreateFile2((const wchar_t *)path.constData(),
                 GENERIC_READ | GENERIC_WRITE,
-                FILE_SHARE_READ | FILE_SHARE_WRITE, CREATE_NEW,
+                shareMode, CREATE_NEW,
                 NULL);
 #  endif // Q_OS_WINRT
 
@@ -182,6 +184,7 @@ static bool createFileFromTemplate(NativeFileHandle &file,
             return false;
         }
 #else // POSIX
+        Q_UNUSED(flags)
         file = QT_OPEN(path.constData(),
                 QT_OPEN_CREAT | O_EXCL | QT_OPEN_RDWR | QT_OPEN_LARGEFILE,
                 static_cast<mode_t>(mode));
@@ -342,7 +345,7 @@ bool QTemporaryFileEngine::open(QIODevice::OpenMode openMode)
     NativeFileHandle &file = d->fd;
 #endif
 
-    if (!createFileFromTemplate(file, filename, phPos, phLength, fileMode, error)) {
+    if (!createFileFromTemplate(file, filename, phPos, phLength, fileMode, flags, error)) {
         setError(QFile::OpenError, error.toString());
         return false;
     }
diff --git a/src/corelib/io/qtemporaryfile_p.h b/src/corelib/io/qtemporaryfile_p.h
index 7f365f0e8a..b0fab3a255 100644
--- a/src/corelib/io/qtemporaryfile_p.h
+++ b/src/corelib/io/qtemporaryfile_p.h
@@ -85,6 +85,10 @@ class QTemporaryFileEngine : public QFSFileEngine
 {
     Q_DECLARE_PRIVATE(QFSFileEngine)
 public:
+    enum Flags { Win32NonShared = 0x1 };
+
+    explicit QTemporaryFileEngine(int _flags = 0) : flags(_flags) {}
+
     void initialize(const QString &file, quint32 mode, bool nameIsTemplate = true)
     {
         Q_D(QFSFileEngine);
@@ -109,6 +113,7 @@ public:
     bool close() override;
 
     quint32 fileMode;
+    int flags;
     bool filePathIsTemplate;
     bool filePathWasTemplate;
 };