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#ifndef __KERNEL__
  35#include <stdint.h>
  36#endif
  37#include <linux/types.h>
  38#include <linux/virtio_types.h>
  39
  40/* This marks a buffer as continuing via the next field. */
  41#define VRING_DESC_F_NEXT       1
  42/* This marks a buffer as write-only (otherwise read-only). */
  43#define VRING_DESC_F_WRITE      2
  44/* This means the buffer contains a list of buffer descriptors. */
  45#define VRING_DESC_F_INDIRECT   4
  46
  47/* The Host uses this in used->flags to advise the Guest: don't kick me when
  48 * you add a buffer.  It's unreliable, so it's simply an optimization.  Guest
  49 * will still kick if it's out of buffers. */
  50#define VRING_USED_F_NO_NOTIFY  1
  51/* The Guest uses this in avail->flags to advise the Host: don't interrupt me
  52 * when you consume a buffer.  It's unreliable, so it's simply an
  53 * optimization.  */
  54#define VRING_AVAIL_F_NO_INTERRUPT      1
  55
  56/* We support indirect buffer descriptors */
  57#define VIRTIO_RING_F_INDIRECT_DESC     28
  58
  59/* The Guest publishes the used index for which it expects an interrupt
  60 * at the end of the avail ring. Host should ignore the avail->flags field. */
  61/* The Host publishes the avail index for which it expects a kick
  62 * at the end of the used ring. Guest should ignore the used->flags field. */
  63#define VIRTIO_RING_F_EVENT_IDX         29
  64
  65/* Virtio ring descriptors: 16 bytes.  These can chain together via "next". */
  66struct vring_desc {
  67        /* Address (guest-physical). */
  68        __virtio64 addr;
  69        /* Length. */
  70        __virtio32 len;
  71        /* The flags as indicated above. */
  72        __virtio16 flags;
  73        /* We chain unused descriptors via this, too */
  74        __virtio16 next;
  75};
  76
  77struct vring_avail {
  78        __virtio16 flags;
  79        __virtio16 idx;
  80        __virtio16 ring[];
  81};
  82
  83/* u32 is used here for ids for padding reasons. */
  84struct vring_used_elem {
  85        /* Index of start of used descriptor chain. */
  86        __virtio32 id;
  87        /* Total length of the descriptor chain which was used (written to) */
  88        __virtio32 len;
  89};
  90
  91struct vring_used {
  92        __virtio16 flags;
  93        __virtio16 idx;
  94        struct vring_used_elem ring[];
  95};
  96
  97struct vring {
  98        unsigned int num;
  99
 100        struct vring_desc *desc;
 101
 102        struct vring_avail *avail;
 103
 104        struct vring_used *used;
 105};
 106
 107/* Alignment requirements for vring elements.
 108 * When using pre-virtio 1.0 layout, these fall out naturally.
 109 */
 110#define VRING_AVAIL_ALIGN_SIZE 2
 111#define VRING_USED_ALIGN_SIZE 4
 112#define VRING_DESC_ALIGN_SIZE 16
 113
 114/* The standard layout for the ring is a continuous chunk of memory which looks
 115 * like this.  We assume num is a power of 2.
 116 *
 117 * struct vring
 118 * {
 119 *      // The actual descriptors (16 bytes each)
 120 *      struct vring_desc desc[num];
 121 *
 122 *      // A ring of available descriptor heads with free-running index.
 123 *      __virtio16 avail_flags;
 124 *      __virtio16 avail_idx;
 125 *      __virtio16 available[num];
 126 *      __virtio16 used_event_idx;
 127 *
 128 *      // Padding to the next align boundary.
 129 *      char pad[];
 130 *
 131 *      // A ring of used descriptor heads with free-running index.
 132 *      __virtio16 used_flags;
 133 *      __virtio16 used_idx;
 134 *      struct vring_used_elem used[num];
 135 *      __virtio16 avail_event_idx;
 136 * };
 137 */
 138/* We publish the used event index at the end of the available ring, and vice
 139 * versa. They are at the end for backwards compatibility. */
 140#define vring_used_event(vr) ((vr)->avail->ring[(vr)->num])
 141#define vring_avail_event(vr) (*(__virtio16 *)&(vr)->used->ring[(vr)->num])
 142
 143static inline void vring_init(struct vring *vr, unsigned int num, void *p,
 144                              unsigned long align)
 145{
 146        vr->num = num;
 147        vr->desc = p;
 148        vr->avail = p + num*sizeof(struct vring_desc);
 149        vr->used = (void *)(((uintptr_t)&vr->avail->ring[num] + sizeof(__virtio16)
 150                + align-1) & ~(align - 1));
 151}
 152
 153static inline unsigned vring_size(unsigned int num, unsigned long align)
 154{
 155        return ((sizeof(struct vring_desc) * num + sizeof(__virtio16) * (3 + num)
 156                 + align - 1) & ~(align - 1))
 157                + sizeof(__virtio16) * 3 + sizeof(struct vring_used_elem) * num;
 158}
 159
 160/* The following is used with USED_EVENT_IDX and AVAIL_EVENT_IDX */
 161/* Assuming a given event_idx value from the other side, if
 162 * we have just incremented index from old to new_idx,
 163 * should we trigger an event? */
 164static inline int vring_need_event(__u16 event_idx, __u16 new_idx, __u16 old)
 165{
 166        /* Note: Xen has similar logic for notification hold-off
 167         * in include/xen/interface/io/ring.h with req_event and req_prod
 168         * corresponding to event_idx + 1 and new_idx respectively.
 169         * Note also that req_event and req_prod in Xen start at 1,
 170         * event indexes in virtio start at 0. */
 171        return (__u16)(new_idx - event_idx - 1) < (__u16)(new_idx - old);
 172}
 173
 174#endif /* _UAPI_LINUX_VIRTIO_RING_H */
 175