LXR linux/include/uapi/linux/virtio

   1#ifndef _UAPI_LINUX_VIRTIO_RING_H
   2#define _UAPI_LINUX_VIRTIO_RING_H
   3/* An interface for efficient virtio implementation, currently for use by KVM
   4 * and lguest, but hopefully others soon.  Do NOT change this since it will
   5 * break existing servers and clients.
   6 *
   7 * This header is BSD licensed so anyone can use the definitions to implement
   8 * compatible drivers/servers.
   9 *
  10 * Redistribution and use in source and binary forms, with or without
  11 * modification, are permitted provided that the following conditions
  12 * are met:
  13 * 1. Redistributions of source code must retain the above copyright
  14 *    notice, this list of conditions and the following disclaimer.
  15 * 2. Redistributions in binary form must reproduce the above copyright
  16 *    notice, this list of conditions and the following disclaimer in the
  17 *    documentation and/or other materials provided with the distribution.
  18 * 3. Neither the name of IBM nor the names of its contributors
  19 *    may be used to endorse or promote products derived from this software
  20 *    without specific prior written permission.
  21 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS ``AS IS'' AND
  22 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  23 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  24 * ARE DISCLAIMED.  IN NO EVENT SHALL IBM OR CONTRIBUTORS BE LIABLE
  25 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  26 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  27 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  28 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  29 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  30 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  31 * SUCH DAMAGE.
  32 *
  33 * Copyright Rusty Russell IBM Corporation 2007. */
  34#include <linux/types.h>
  35
  36/* This marks a buffer as continuing via the next field. */
  37#define VRING_DESC_F_NEXT       1
  38/* This marks a buffer as write-only (otherwise read-only). */
  39#define VRING_DESC_F_WRITE      2
  40/* This means the buffer contains a list of buffer descriptors. */
  41#define VRING_DESC_F_INDIRECT   4
  42
  43/* The Host uses this in used->flags to advise the Guest: don't kick me when
  44 * you add a buffer.  It's unreliable, so it's simply an optimization.  Guest
  45 * will still kick if it's out of buffers. */
  46#define VRING_USED_F_NO_NOTIFY  1
  47/* The Guest uses this in avail->flags to advise the Host: don't interrupt me
  48 * when you consume a buffer.  It's unreliable, so it's simply an
  49 * optimization.  */
  50#define VRING_AVAIL_F_NO_INTERRUPT      1
  51
  52/* We support indirect buffer descriptors */
  53#define VIRTIO_RING_F_INDIRECT_DESC     28
  54
  55/* The Guest publishes the used index for which it expects an interrupt
  56 * at the end of the avail ring. Host should ignore the avail->flags field. */
  57/* The Host publishes the avail index for which it expects a kick
  58 * at the end of the used ring. Guest should ignore the used->flags field. */
  59#define VIRTIO_RING_F_EVENT_IDX         29
  60
  61/* Virtio ring descriptors: 16 bytes.  These can chain together via "next". */
  62struct vring_desc {
  63        /* Address (guest-physical). */
  64        __u64 addr;
  65        /* Length. */
  66        __u32 len;
  67        /* The flags as indicated above. */
  68        __u16 flags;
  69        /* We chain unused descriptors via this, too */
  70        __u16 next;
  71};
  72
  73struct vring_avail {
  74        __u16 flags;
  75        __u16 idx;
  76        __u16 ring[];
  77};
  78
  79/* u32 is used here for ids for padding reasons. */
  80struct vring_used_elem {
  81        /* Index of start of used descriptor chain. */
  82        __u32 id;
  83        /* Total length of the descriptor chain which was used (written to) */
  84        __u32 len;
  85};
  86
  87struct vring_used {
  88        __u16 flags;
  89        __u16 idx;
  90        struct vring_used_elem ring[];
  91};
  92
  93struct vring {
  94        unsigned int num;
  95
  96        struct vring_desc *desc;
  97
  98        struct vring_avail *avail;
  99
 100        struct vring_used *used;
 101};
 102
 103/* The standard layout for the ring is a continuous chunk of memory which looks
 104 * like this.  We assume num is a power of 2.
 105 *
 106 * struct vring
 107 * {
 108 *      // The actual descriptors (16 bytes each)
 109 *      struct vring_desc desc[num];
 110 *
 111 *      // A ring of available descriptor heads with free-running index.
 112 *      __u16 avail_flags;
 113 *      __u16 avail_idx;
 114 *      __u16 available[num];
 115 *      __u16 used_event_idx;
 116 *
 117 *      // Padding to the next align boundary.
 118 *      char pad[];
 119 *
 120 *      // A ring of used descriptor heads with free-running index.
 121 *      __u16 used_flags;
 122 *      __u16 used_idx;
 123 *      struct vring_used_elem used[num];
 124 *      __u16 avail_event_idx;
 125 * };
 126 */
 127/* We publish the used event index at the end of the available ring, and vice
 128 * versa. They are at the end for backwards compatibility. */
 129#define vring_used_event(vr) ((vr)->avail->ring[(vr)->num])
 130#define vring_avail_event(vr) (*(__u16 *)&(vr)->used->ring[(vr)->num])
 131
 132static inline void vring_init(struct vring *vr, unsigned int num, void *p,
 133                              unsigned long align)
 134{
 135        vr->num = num;
 136        vr->desc = p;
 137        vr->avail = p + num*sizeof(struct vring_desc);
 138        vr->used = (void *)(((unsigned long)&vr->avail->ring[num] + sizeof(__u16)
 139                + align-1) & ~(align - 1));
 140}
 141
 142static inline unsigned vring_size(unsigned int num, unsigned long align)
 143{
 144        return ((sizeof(struct vring_desc) * num + sizeof(__u16) * (3 + num)
 145                 + align - 1) & ~(align - 1))
 146                + sizeof(__u16) * 3 + sizeof(struct vring_used_elem) * num;
 147}
 148
 149/* The following is used with USED_EVENT_IDX and AVAIL_EVENT_IDX */
 150/* Assuming a given event_idx value from the other size, if
 151 * we have just incremented index from old to new_idx,
 152 * should we trigger an event? */
 153static inline int vring_need_event(__u16 event_idx, __u16 new_idx, __u16 old)
 154{
 155        /* Note: Xen has similar logic for notification hold-off
 156         * in include/xen/interface/io/ring.h with req_event and req_prod
 157         * corresponding to event_idx + 1 and new_idx respectively.
 158         * Note also that req_event and req_prod in Xen start at 1,
 159         * event indexes in virtio start at 0. */
 160        return (__u16)(new_idx - event_idx - 1) < (__u16)(new_idx - old);
 161}
 162
 163#endif /* _UAPI_LINUX_VIRTIO_RING_H */
 164