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>

3 files changed, 13 insertions, 7 deletions

diff --git a/src/corelib/io/qsavefile.cpp b/src/corelib/io/qsavefile.cpp
index 56934a9a0f..0cbc8c2234 100644
--- a/src/corelib/io/qsavefile.cpp
+++ b/src/corelib/io/qsavefile.cpp
@@ -264,7 +264,7 @@ bool QSaveFile::open(OpenMode mode)
     }
 #endif
 
-    d->fileEngine = new QTemporaryFileEngine(&d->finalFileName);
+    d->fileEngine = new QTemporaryFileEngine(&d->finalFileName, 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 73249d7df8..1983a22c65 100644
--- a/src/corelib/io/qtemporaryfile.cpp
+++ b/src/corelib/io/qtemporaryfile.cpp
@@ -207,7 +207,7 @@ QFileSystemEntry::NativePath QTemporaryFileName::generateNext()
     changed and contain the generated path name.
 */
 static bool createFileFromTemplate(NativeFileHandle &file, QTemporaryFileName &templ,
-                                   quint32 mode, QSystemError &error)
+                                   quint32 mode, int flags, QSystemError &error)
 {
     const int maxAttempts = 16;
     for (int attempt = 0; attempt < maxAttempts; ++attempt) {
@@ -216,16 +216,18 @@ static bool createFileFromTemplate(NativeFileHandle &file, QTemporaryFileName &t
 
 #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
 
@@ -247,6 +249,7 @@ static bool createFileFromTemplate(NativeFileHandle &file, QTemporaryFileName &t
             return false;
         }
 #else // POSIX
+        Q_UNUSED(flags)
         file = QT_OPEN(path.constData(),
                 QT_OPEN_CREAT | QT_OPEN_EXCL | QT_OPEN_RDWR | QT_OPEN_LARGEFILE,
                 static_cast<mode_t>(mode));
@@ -366,7 +369,7 @@ bool QTemporaryFileEngine::open(QIODevice::OpenMode openMode)
         unnamedFile = true;
         d->fileEntry.clear();
     } else if (st == CreateUnnamedFileStatus::NotSupported &&
-               createFileFromTemplate(file, tfn, fileMode, error)) {
+               createFileFromTemplate(file, tfn, fileMode, flags, error)) {
         filePathIsTemplate = false;
         unnamedFile = false;
         d->fileEntry = QFileSystemEntry(tfn.path, QFileSystemEntry::FromNativePath());
diff --git a/src/corelib/io/qtemporaryfile_p.h b/src/corelib/io/qtemporaryfile_p.h
index fb8887af53..0fec88d3cd 100644
--- a/src/corelib/io/qtemporaryfile_p.h
+++ b/src/corelib/io/qtemporaryfile_p.h
@@ -108,8 +108,10 @@ class QTemporaryFileEngine : public QFSFileEngine
 {
     Q_DECLARE_PRIVATE(QFSFileEngine)
 public:
-    QTemporaryFileEngine(const QString *templateName)
-        : templateName(*templateName)
+    enum Flags { Win32NonShared = 0x1 };
+
+    explicit QTemporaryFileEngine(const QString *_templateName, int _flags = 0)
+        : templateName(*_templateName), flags(_flags)
     {}
 
     void initialize(const QString &file, quint32 mode, bool nameIsTemplate = true)
@@ -144,6 +146,7 @@ public:
 
     const QString &templateName;
     quint32 fileMode;
+    int flags = 0;
     bool filePathIsTemplate;
     bool filePathWasTemplate;
     bool unnamedFile = false;