Add syncToDisk() to QAbstractFileEngine.

This is needed by QSaveFile.

Change-Id: I07ebdfd832c0be65c26f0aed1bb7852ac33135ca
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/io/qabstractfileengine.cpp

@@ -399,6 +399,19 @@ bool QAbstractFileEngine::close()
     return false;
 }
 
+/*!
+    \since 5.1
+
+    Flushes and syncs the file to disk.
+
+    Returns true if successful; otherwise returns false.
+    The default implementation always returns false.
+*/
+bool QAbstractFileEngine::syncToDisk()
+{
+    return false;
+}
+
 /*!
     Flushes the open file, returning true if successful; otherwise returns
     false.

src/corelib/io/qabstractfileengine_p.h

@@ -124,6 +124,7 @@ public:
     virtual bool open(QIODevice::OpenMode openMode);
     virtual bool close();
     virtual bool flush();
+    virtual bool syncToDisk();
     virtual qint64 size() const;
     virtual qint64 pos() const;
     virtual bool seek(qint64 pos);

src/corelib/io/qfsfileengine.cpp

@@ -418,6 +418,17 @@ bool QFSFileEngine::flush()
     return d->nativeFlush();
 }
 
+/*!
+    \reimp
+*/
+bool QFSFileEngine::syncToDisk()
+{
+    Q_D(QFSFileEngine);
+    if ((d->openMode & QIODevice::WriteOnly) == 0)
+        return true;
+    return d->nativeSyncToDisk();
+}
+
 /*!
     \internal
 */

src/corelib/io/qfsfileengine_p.h

@@ -81,6 +81,7 @@ public:
     bool open(QIODevice::OpenMode flags, FILE *fh);
     bool close();
     bool flush();
+    bool syncToDisk();
     qint64 size() const;
     qint64 pos() const;
     bool seek(qint64);
@@ -150,6 +151,7 @@ public:
     bool nativeClose();
     bool closeFdFh();
     bool nativeFlush();
+    bool nativeSyncToDisk();
     bool flushFh();
     qint64 nativeSize() const;
 #ifndef Q_OS_WIN

src/corelib/io/qfsfileengine_unix.cpp

@@ -256,6 +256,23 @@ bool QFSFileEnginePrivate::nativeFlush()
     return fh ? flushFh() : fd != -1;
 }
 
+/*!
+    \internal
+    \since 5.1
+*/
+bool QFSFileEnginePrivate::nativeSyncToDisk()
+{
+    Q_Q(QFSFileEngine);
+#if defined(_POSIX_SYNCHRONIZED_IO) && _POSIX_SYNCHRONIZED_IO > 0
+    const int ret = fdatasync(nativeHandle());
+#else
+    const int ret = fsync(nativeHandle());
+#endif
+    if (ret != 0)
+        q->setError(QFile::WriteError, qt_error_string(errno));
+    return ret == 0;
+}
+
 /*!
     \internal
 */

src/corelib/io/qfsfileengine_win.cpp

@@ -198,13 +198,23 @@ bool QFSFileEnginePrivate::nativeFlush()
         return true;
     }
 
-    // Windows native mode; flushing is
+    // Windows native mode; flushing is unnecessary.
-    // unnecessary. FlushFileBuffers(), the equivalent of sync() or
-    // fsync() on Unix, does a low-level flush to the disk, and we
-    // don't expose an API for this.
     return true;
 }
 
+/*
+    \internal
+    \since 5.1
+*/
+bool QFSFileEnginePrivate::nativeSyncToDisk()
+{
+    if (fh || fd != -1) {
+        // stdlib / stdio mode. No API available.
+        return false;
+    }
+    return FlushFileBuffers(fileHandle);
+}
+
 /*
     \internal
 */