LXR qemu/include/standard-headers/linux/virtio

   1#ifndef _LINUX_VIRTIO_RING_H
   2#define _LINUX_VIRTIO_RING_H
   3/* An interface for efficient virtio implementation, currently for use by KVM,
   4 * 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 <stdint.h>
  35#include "standard-headers/linux/types.h"
  36#include "standard-headers/linux/virtio_types.h"
  37
  38/* This marks a buffer as continuing via the next field. */
  39#define VRING_DESC_F_NEXT       1
  40/* This marks a buffer as write-only (otherwise read-only). */
  41#define VRING_DESC_F_WRITE      2
  42/* This means the buffer contains a list of buffer descriptors. */
  43#define VRING_DESC_F_INDIRECT   4
  44
  45/* The Host uses this in used->flags to advise the Guest: don't kick me when
  46 * you add a buffer.  It's unreliable, so it's simply an optimization.  Guest
  47 * will still kick if it's out of buffers. */
  48#define VRING_USED_F_NO_NOTIFY  1
  49/* The Guest uses this in avail->flags to advise the Host: don't interrupt me
  50 * when you consume a buffer.  It's unreliable, so it's simply an
  51 * optimization.  */
  52#define VRING_AVAIL_F_NO_INTERRUPT      1
  53
  54/* We support indirect buffer descriptors */
  55#define VIRTIO_RING_F_INDIRECT_DESC     28
  56
  57/* The Guest publishes the used index for which it expects an interrupt
  58 * at the end of the avail ring. Host should ignore the avail->flags field. */
  59/* The Host publishes the avail index for which it expects a kick
  60 * at the end of the used ring. Guest should ignore the used->flags field. */
  61#define VIRTIO_RING_F_EVENT_IDX         29
  62
  63/* Virtio ring descriptors: 16 bytes.  These can chain together via "next". */
  64struct vring_desc {
  65        /* Address (guest-physical). */
  66        __virtio64 addr;
  67        /* Length. */
  68        __virtio32 len;
  69        /* The flags as indicated above. */
  70        __virtio16 flags;
  71        /* We chain unused descriptors via this, too */
  72        __virtio16 next;
  73};
  74
  75struct vring_avail {
  76        __virtio16 flags;
  77        __virtio16 idx;
  78        __virtio16 ring[];
  79};
  80
  81/* uint32_t is used here for ids for padding reasons. */
  82struct vring_used_elem {
  83        /* Index of start of used descriptor chain. */
  84        __virtio32 id;
  85        /* Total length of the descriptor chain which was used (written to) */
  86        __virtio32 len;
  87};
  88
  89struct vring_used {
  90        __virtio16 flags;
  91        __virtio16 idx;
  92        struct vring_used_elem ring[];
  93};
  94
  95struct vring {
  96        unsigned int num;
  97
  98        struct vring_desc *desc;
  99
 100        struct vring_avail *avail;
 101
 102        struct vring_used *used;
 103};
 104
 105/* Alignment requirements for vring elements.
 106 * When using pre-virtio 1.0 layout, these fall out naturally.
 107 */
 108#define VRING_AVAIL_ALIGN_SIZE 2
 109#define VRING_USED_ALIGN_SIZE 4
 110#define VRING_DESC_ALIGN_SIZE 16
 111
 112/* The standard layout for the ring is a continuous chunk of memory which looks
 113 * like this.  We assume num is a power of 2.
 114 *
 115 * struct vring
 116 * {
 117 *      // The actual descriptors (16 bytes each)
 118 *      struct vring_desc desc[num];
 119 *
 120 *      // A ring of available descriptor heads with free-running index.
 121 *      __virtio16 avail_flags;
 122 *      __virtio16 avail_idx;
 123 *      __virtio16 available[num];
 124 *      __virtio16 used_event_idx;
 125 *
 126 *      // Padding to the next align boundary.
 127 *      char pad[];
 128 *
 129 *      // A ring of used descriptor heads with free-running index.
 130 *      __virtio16 used_flags;
 131 *      __virtio16 used_idx;
 132 *      struct vring_used_elem used[num];
 133 *      __virtio16 avail_event_idx;
 134 * };
 135 */
 136/* We publish the used event index at the end of the available ring, and vice
 137 * versa. They are at the end for backwards compatibility. */
 138#define vring_used_event(vr) ((vr)->avail->ring[(vr)->num])
 139#define vring_avail_event(vr) (*(__virtio16 *)&(vr)->used->ring[(vr)->num])
 140
 141static inline void vring_init(struct vring *vr, unsigned int num, void *p,
 142                              unsigned long align)
 143{
 144        vr->num = num;
 145        vr->desc = p;
 146        vr->avail = p + num*sizeof(struct vring_desc);
 147        vr->used = (void *)(((uintptr_t)&vr->avail->ring[num] + sizeof(__virtio16)
 148                + align-1) & ~(align - 1));
 149}
 150
 151static inline unsigned vring_size(unsigned int num, unsigned long align)
 152{
 153        return ((sizeof(struct vring_desc) * num + sizeof(__virtio16) * (3 + num)
 154                 + align - 1) & ~(align - 1))
 155                + sizeof(__virtio16) * 3 + sizeof(struct vring_used_elem) * num;
 156}
 157
 158/* The following is used with USED_EVENT_IDX and AVAIL_EVENT_IDX */
 159/* Assuming a given event_idx value from the other side, if
 160 * we have just incremented index from old to new_idx,
 161 * should we trigger an event? */
 162static inline int vring_need_event(uint16_t event_idx, uint16_t new_idx, uint16_t old)
 163{
 164        /* Note: Xen has similar logic for notification hold-off
 165         * in include/xen/interface/io/ring.h with req_event and req_prod
 166         * corresponding to event_idx + 1 and new_idx respectively.
 167         * Note also that req_event and req_prod in Xen start at 1,
 168         * event indexes in virtio start at 0. */
 169        return (uint16_t)(new_idx - event_idx - 1) < (uint16_t)(new_idx - old);
 170}
 171
 172#endif /* _LINUX_VIRTIO_RING_H */
 173