    /**
     * @file
     * @section AUTHORS
     *
     * Copyright (C) 2010  Rafal Wojtczuk  <rafal@invisiblethingslab.com>
     *
     *  Authors:
     *       Rafal Wojtczuk  <rafal@invisiblethingslab.com>
     *       Daniel De Graaf <dgdegra@tycho.nsa.gov>
     *
     * @section LICENSE
     *
     * Permission is hereby granted, free of charge, to any person obtaining a copy
     * of this software and associated documentation files (the "Software"), to
     * deal in the Software without restriction, including without limitation the
     * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
     * sell copies of the Software, and to permit persons to whom the Software is
     * furnished to do so, subject to the following conditions:
     *
     * The above copyright notice and this permission notice shall be included in
     * all copies or substantial portions of the Software.
     *
     * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
     * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
     * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
     * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
     * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
     * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
     * DEALINGS IN THE SOFTWARE.
     *
     * @section DESCRIPTION
     *
     *  Originally borrowed from the Qubes OS Project, http://www.qubes-os.org,
     *  this code has been substantially rewritten to use the gntdev and gntalloc
     *  devices instead of raw MFNs and map_foreign_range.
     *
     *  This is a library for inter-domain communication.  A standard Xen ring
     *  buffer is used, with a datagram-based interface built on top.  The grant
     *  reference and event channels are shared in XenStore under a user-specified
     *  path.
     *
     *  The ring.h macros define an asymmetric interface to a shared data structure
     *  that assumes all rings reside in a single contiguous memory space. This is
     *  not suitable for vchan because the interface to the ring is symmetric except
     *  for the setup. Unlike the producer-consumer rings defined in ring.h, the
     *  size of the rings used in vchan are determined at execution time instead of
     *  compile time, so the macros in ring.h cannot be used to access the rings.
     */

    #include <stdint.h>
    #include <sys/types.h>

    struct ring_shared {
    	uint32_t cons, prod;
    };

    #define VCHAN_NOTIFY_WRITE 0x1
    #define VCHAN_NOTIFY_READ 0x2

    /**
     * vchan_interface: primary shared data structure
     */
    struct vchan_interface {
    	/**
    	 * Standard consumer/producer interface, one pair per buffer
    	 * left is client write, server read
    	 * right is client read, server write
    	 */
    	struct ring_shared left, right;
    	/**
    	 * size of the rings, which determines their location
    	 * 10   - at offset 1024 in ring's page
    	 * 11   - at offset 2048 in ring's page
    	 * 12+  - uses 2^(N-12) grants to describe the multi-page ring
    	 * These should remain constant once the page is shared.
    	 * Only one of the two orders can be 10 (or 11).
    	 */
    	uint16_t left_order, right_order;
    	/**
    	 * Shutdown detection:
    	 *  0: client (or server) has exited
    	 *  1: client (or server) is connected
    	 *  2: client has not yet connected
    	 */
    	uint8_t cli_live, srv_live;
    	/**
    	 * Notification bits:
    	 *  VCHAN_NOTIFY_WRITE: send notify when data is written
    	 *  VCHAN_NOTIFY_READ: send notify when data is read (consumed)
    	 * cli_notify is used for the client to inform the server of its action
    	 */
    	uint8_t cli_notify, srv_notify;
    	/**
    	 * Grant list: ordering is left, right. Must not extend into actual ring
    	 * or grow beyond the end of the initial shared page.
    	 * These should remain constant once the page is shared, to allow
    	 * for possible remapping by a client that restarts.
    	 */
    	uint32_t grants[0];
    };