FreeBSD/Linux Kernel Cross Reference
sys/xen/interface/io/libxenvchan.h

     /**
      * @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
     *
     *  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 2.1 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, write to the Free Software
     *  Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301 USA
     *
     * @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];
    };
    

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