copy messages directly from sender into a receiver-supplied buffer

Require the receiver to pre-allocate a buffer and register it with
HELLO. The sender will copy its data directly into the revceiver's
buffer.

The RECV call will now only return a pointer to the next message
in the buffer. The buffer needs to be free()d with the FREE ioctl.

FIXME: currently missing is a proper allocator to manage the
receiver's buffer, in the current state the allocator will only clear
the buffer if all messages are free()d. This is obviously only useful
for testing.

1 files changed, 52 insertions, 0 deletions

diff --git a/buffer.h b/buffer.h
new file mode 100644
index 00000000000..0cdb065d870
--- /dev/null
+++ b/buffer.h
@@ -0,0 +1,52 @@
+/*
+ * Copyright (C) 2013 Kay Sievers
+ * Copyright (C) 2013 Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+ * Copyright (C) 2013 Linux Foundation
+ * Copyright (C) 2013 Daniel Mack <daniel@zonque.org>
+ *
+ * kdbus 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 2.1 of the License, or (at
+ * your option) any later version.
+ */
+
+#ifndef __KDBUS_BUFFER_H
+#define __KDBUS_BUFFER_H
+
+/*
+ * At KDBUS_CMD_MSG_SEND, messages are placed direcly into the buffer the
+ * receiver has registered with KDBUS_HELLO_BUFFER.
+ *
+ * To receive a message, KDBUS_CMD_MSG_RECV is called, which returns a pointer
+ * into the buffer.
+ *
+ * The internally allocated memory needs to be freed by the receiver with
+ * KDBUS_CMD_MSG_FREE.
+ */
+struct kdbus_buffer {
+	void __user *buf;	/* receiver-supplied buffer */
+	size_t size;		/* size of buffer  */
+	size_t pos;		/* current write position */
+	unsigned int users;
+};
+
+/*
+ * Structure to keep the state of a mapped range on the buffer while
+ * writing chunks of data to it from the sender.
+ */
+struct kdbus_buffer_map {
+	struct page **pages;	/* array of pages representign the buffer */
+	unsigned int n;		/* number pf pages in the array */
+	unsigned long cur;	/* current page we write to */
+	unsigned long pos;	/* position in current page we write to */
+};
+
+struct kdbus_msg __user *kdbus_buffer_alloc(struct kdbus_buffer *buf, size_t len);
+void kdbus_buffer_free(struct kdbus_buffer *buf, struct kdbus_msg __user *msg);
+void kdbus_buffer_map_close(struct kdbus_buffer *buf);
+int kdbus_buffer_map_open(struct kdbus_buffer *buf,
+			  struct task_struct *task,
+			  void __user *to, size_t len);
+int kdbus_buffer_map_write(struct kdbus_buffer *buf,
+			   void __user *from, size_t len);
+#endif