buffer: add buffer_move_empty

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Peter Lieven <pl@kamp.de>
Reviewed-by: Daniel Berrange <berrange@redhat.com>
Message-id: 1446203414-4013-4-git-send-email-kraxel@redhat.com

include/qemu/buffer.h

diff --git a/include/qemu/buffer.h b/include/qemu/buffer.h
index 0710e16..f53ee9e 100644
--- a/include/qemu/buffer.h
+++ b/include/qemu/buffer.h
@@ -127,4 +127,14 @@
  */
 gboolean buffer_empty(Buffer *buffer);
 
+/**
+ * buffer_move_empty:
+ * @to: destination buffer object
+ * @from: source buffer object
+ *
+ * Moves buffer, without copying data.  'to' buffer must be empty.
+ * 'from' buffer is empty and zero-sized on return.
+ */
+void buffer_move_empty(Buffer *to, Buffer *from);
+
 #endif /* QEMU_BUFFER_H__ */

util/buffer.c

diff --git a/util/buffer.c b/util/buffer.c
index 12bf2d7..c7a39ec 100644
--- a/util/buffer.c
+++ b/util/buffer.c
@@ -77,3 +77,17 @@
             (buffer->offset - len));
     buffer->offset -= len;
 }
+
+void buffer_move_empty(Buffer *to, Buffer *from)
+{
+    assert(to->offset == 0);
+
+    g_free(to->buffer);
+    to->offset = from->offset;
+    to->capacity = from->capacity;
+    to->buffer = from->buffer;
+
+    from->offset = 0;
+    from->capacity = 0;
+    from->buffer = NULL;
+}