io: add QIOChannelBuffer class

Add a QIOChannel subclass that is capable of performing I/O
to/from a memory buffer. This implementation does not attempt
to support concurrent readers & writers. It is designed for
serialized access where by a single thread at a time may write
data, seek and then read data back out.

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>

include/io/channel-buffer.h

@@ -0,0 +1,60 @@
+/*
+ * QEMU I/O channels memory buffer driver
+ *
+ * Copyright (c) 2015 Red Hat, Inc.
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+#ifndef QIO_CHANNEL_BUFFER_H__
+#define QIO_CHANNEL_BUFFER_H__
+
+#include "io/channel.h"
+
+#define TYPE_QIO_CHANNEL_BUFFER "qio-channel-buffer"
+#define QIO_CHANNEL_BUFFER(obj)                                     \
+    OBJECT_CHECK(QIOChannelBuffer, (obj), TYPE_QIO_CHANNEL_BUFFER)
+
+typedef struct QIOChannelBuffer QIOChannelBuffer;
+
+/**
+ * QIOChannelBuffer:
+ *
+ * The QIOChannelBuffer object provides a channel implementation
+ * that is able to perform I/O to/from a memory buffer.
+ *
+ */
+
+struct QIOChannelBuffer {
+    QIOChannel parent;
+    size_t capacity; /* Total allocated memory */
+    size_t usage;    /* Current size of data */
+    size_t offset;   /* Offset for future I/O ops */
+    char *data;
+};
+
+
+/**
+ * qio_channel_buffer_new:
+ * @capacity: the initial buffer capacity to allocate
+ *
+ * Allocate a new buffer which is initially empty
+ *
+ * Returns: the new channel object
+ */
+QIOChannelBuffer *
+qio_channel_buffer_new(size_t capacity);
+
+#endif /* QIO_CHANNEL_BUFFER_H__ */