Fix QAbstractFileEngine::clone misuse

QFile::copy was assuming that the target file was native and therefore
it could simply take the file descriptor to clone. While that was not
currently a problem, in theory it could be as we do have one writeable
file engine besides QFSFileEngine (QWinRTFileEngine).

By refactoring to take the parameter as a QAbstractFileEngine, we can
ensure that the target file is a native file.

Change-Id: Ib7a1737987bf4c4a8c51fffd14d0c048fd509025
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@qt.io>
Reviewed-by: Lars Knoll <lars.knoll@qt.io>

src/corelib/io/qabstractfileengine.cpp

@@ -864,13 +864,14 @@ bool QAbstractFileEngine::unmap(uchar *address)
 /*!
     \since 5.10
 
-    Copies the contents from the file specified by \a sourceHandle to this file
+    Duplicates the contents of this file (starting from the current position)
-    by cloning it.
+    to the file specified by the engine \a target.
+
     Returns \c true on success; otherwise, \c false is returned.
  */
-bool QAbstractFileEngine::clone(int sourceHandle)
+bool QAbstractFileEngine::cloneTo(QAbstractFileEngine *target)
 {
-    Q_UNUSED(sourceHandle);
+    Q_UNUSED(target);
     return false;
 }
 

src/corelib/io/qabstractfileengine_p.h

@@ -150,7 +150,7 @@ public:
     virtual QDateTime fileTime(FileTime time) const;
     virtual void setFileName(const QString &file);
     virtual int handle() const;
-    virtual bool clone(int sourceHandle);
+    virtual bool cloneTo(QAbstractFileEngine *target);
     bool atEnd() const;
     uchar *map(qint64 offset, qint64 size, QFile::MemoryMapFlags flags);
     bool unmap(uchar *ptr);

src/corelib/io/qfile.cpp

@@ -804,7 +804,7 @@ QFile::copy(const QString &newName)
                     close();
                     d->setError(QFile::CopyError, tr("Cannot open for output"));
                 } else {
-                    if (!out.d_func()->engine()->clone(d->engine()->handle())) {
+                    if (!d->engine()->cloneTo(out.d_func()->engine())) {
                         char block[4096];
                         qint64 totalRead = 0;
                         while (!atEnd()) {

src/corelib/io/qfsfileengine_p.h

@@ -110,7 +110,7 @@ public:
     qint64 read(char *data, qint64 maxlen) Q_DECL_OVERRIDE;
     qint64 readLine(char *data, qint64 maxlen) Q_DECL_OVERRIDE;
     qint64 write(const char *data, qint64 len) Q_DECL_OVERRIDE;
-    bool clone(int sourceHandle) override;
+    bool cloneTo(QAbstractFileEngine *target) override;
 
     bool extension(Extension extension, const ExtensionOption *option = 0, ExtensionReturn *output = 0) Q_DECL_OVERRIDE;
     bool supportsExtension(Extension extension) const Q_DECL_OVERRIDE;

src/corelib/io/qfsfileengine_unix.cpp

@@ -735,16 +735,19 @@ bool QFSFileEnginePrivate::unmap(uchar *ptr)
 /*!
     \reimp
 */
-bool QFSFileEngine::clone(int sourceHandle)
+bool QFSFileEngine::cloneTo(QAbstractFileEngine *target)
 {
+    if ((target->fileFlags(LocalDiskFlag) & LocalDiskFlag) == 0)
+        return false;
 #if defined(Q_OS_LINUX)
     Q_D(QFSFileEngine);
 #  if !defined FICLONE
 #    define FICLONE _IOW (0x94, 9, int)
 #  endif
-    return ::ioctl(d->fd, FICLONE, sourceHandle) == 0;
+    int srcfd = d->nativeHandle();
+    int dstfd = target->handle();
+    return ::ioctl(dstfd, FICLONE, srcfd) == 0;
 #else
-    Q_UNUSED(sourceHandle);
     return false;
 #endif
 }

src/corelib/io/qfsfileengine_win.cpp

@@ -1032,9 +1032,11 @@ bool QFSFileEnginePrivate::unmap(uchar *ptr)
 /*!
     \reimp
 */
-bool QFSFileEngine::clone(int sourceHandle)
+bool QFSFileEngine::cloneTo(QAbstractFileEngine *target)
 {
-    Q_UNUSED(sourceHandle);
+    // There's some Windows Server 2016 API, but we won't
+    // bother with it.
+    Q_UNUSED(target);
     return false;
 }