Speed up QFile::copy on Linux file systems that support cloning

Originally inherited from Btrfs, recent Linux kernels have a system call
that allows cloning the contents of a file from another one if the
underlying file system supports it.

Change-Id: I9df66b65faef99f3bbed8a88fb6b6009baeef32e
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/io/qabstractfileengine.cpp

@@ -831,6 +831,19 @@ bool QAbstractFileEngine::unmap(uchar *address)
     return extension(UnMapExtension, &options);
 }
 
+/*!
+    \since 5.10
+
+    Copies the contents from the file specified by \a sourceHandle to this file
+    by cloning it.
+    Returns \c true on success; otherwise, \c false is returned.
+ */
+bool QAbstractFileEngine::clone(int sourceHandle)
+{
+    Q_UNUSED(sourceHandle);
+    return false;
+}
+
 /*!
     \since 4.3
     \class QAbstractFileEngineIterator

src/corelib/io/qabstractfileengine_p.h

@@ -147,6 +147,7 @@ public:
     virtual QDateTime fileTime(FileTime time) const;
     virtual void setFileName(const QString &file);
     virtual int handle() const;
+    virtual bool clone(int sourceHandle);
     bool atEnd() const;
     uchar *map(qint64 offset, qint64 size, QFile::MemoryMapFlags flags);
     bool unmap(uchar *ptr);

src/corelib/io/qfile.cpp

@@ -42,6 +42,7 @@
 #include "qfile.h"
 #include "qfsfileengine_p.h"
 #include "qtemporaryfile.h"
+#include "qtemporaryfile_p.h"
 #include "qlist.h"
 #include "qfileinfo.h"
 #include "private/qiodevice_p.h"
@@ -790,25 +791,27 @@ QFile::copy(const QString &newName)
                     close();
                     d->setError(QFile::CopyError, tr("Cannot open for output"));
                 } else {
-                    char block[4096];
-                    qint64 totalRead = 0;
-                    while(!atEnd()) {
-                        qint64 in = read(block, sizeof(block));
-                        if (in <= 0)
-                            break;
-                        totalRead += in;
-                        if(in != out.write(block, in)) {
-                            close();
-                            d->setError(QFile::CopyError, tr("Failure to write block"));
-                            error = true;
-                            break;
+                    if (!out.d_func()->engine()->clone(d->engine()->handle())) {
+                        char block[4096];
+                        qint64 totalRead = 0;
+                        while (!atEnd()) {
+                            qint64 in = read(block, sizeof(block));
+                            if (in <= 0)
+                                break;
+                            totalRead += in;
+                            if (in != out.write(block, in)) {
+                                close();
+                                d->setError(QFile::CopyError, tr("Failure to write block"));
+                                error = true;
+                                break;
+                            }
                         }
-                    }
 
-                    if (totalRead != size()) {
-                        // Unable to read from the source. The error string is
-                        // already set from read().
-                        error = true;
+                        if (totalRead != size()) {
+                            // Unable to read from the source. The error string is
+                            // already set from read().
+                            error = true;
+                        }
                     }
                     if (!error && !out.rename(newName)) {
                         error = true;

src/corelib/io/qfsfileengine_p.h

@@ -108,6 +108,7 @@ 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 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

@@ -780,6 +780,23 @@ bool QFSFileEnginePrivate::unmap(uchar *ptr)
 #endif
 }
 
+/*!
+    \reimp
+*/
+bool QFSFileEngine::clone(int sourceHandle)
+{
+#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;
+#else
+    Q_UNUSED(sourceHandle);
+    return false;
+#endif
+}
+
 QT_END_NAMESPACE
 
 #endif // QT_NO_FSFILEENGINE

src/corelib/io/qfsfileengine_win.cpp

@@ -984,4 +984,13 @@ bool QFSFileEnginePrivate::unmap(uchar *ptr)
     return true;
 }
 
+/*!
+    \reimp
+*/
+bool QFSFileEngine::clone(int sourceHandle)
+{
+    Q_UNUSED(sourceHandle);
+    return false;
+}
+
 QT_END_NAMESPACE

src/corelib/io/qtemporaryfile_p.h

@@ -65,7 +65,7 @@ class QTemporaryFilePrivate : public QFilePrivate
 {
     Q_DECLARE_PUBLIC(QTemporaryFile)
 
-protected:
+public:
     QTemporaryFilePrivate();
     explicit QTemporaryFilePrivate(const QString &templateNameIn);
     ~QTemporaryFilePrivate();