qemu/include/standard-headers/linux/virtio_ring.h
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   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/*
  46 * Mark a descriptor as available or used in packed ring.
  47 * Notice: they are defined as shifts instead of shifted values.
  48 */
  49#define VRING_PACKED_DESC_F_AVAIL       7
  50#define VRING_PACKED_DESC_F_USED        15
  51
  52/* The Host uses this in used->flags to advise the Guest: don't kick me when
  53 * you add a buffer.  It's unreliable, so it's simply an optimization.  Guest
  54 * will still kick if it's out of buffers. */
  55#define VRING_USED_F_NO_NOTIFY  1
  56/* The Guest uses this in avail->flags to advise the Host: don't interrupt me
  57 * when you consume a buffer.  It's unreliable, so it's simply an
  58 * optimization.  */
  59#define VRING_AVAIL_F_NO_INTERRUPT      1
  60
  61/* Enable events in packed ring. */
  62#define VRING_PACKED_EVENT_FLAG_ENABLE  0x0
  63/* Disable events in packed ring. */
  64#define VRING_PACKED_EVENT_FLAG_DISABLE 0x1
  65/*
  66 * Enable events for a specific descriptor in packed ring.
  67 * (as specified by Descriptor Ring Change Event Offset/Wrap Counter).
  68 * Only valid if VIRTIO_RING_F_EVENT_IDX has been negotiated.
  69 */
  70#define VRING_PACKED_EVENT_FLAG_DESC    0x2
  71
  72/*
  73 * Wrap counter bit shift in event suppression structure
  74 * of packed ring.
  75 */
  76#define VRING_PACKED_EVENT_F_WRAP_CTR   15
  77
  78/* We support indirect buffer descriptors */
  79#define VIRTIO_RING_F_INDIRECT_DESC     28
  80
  81/* The Guest publishes the used index for which it expects an interrupt
  82 * at the end of the avail ring. Host should ignore the avail->flags field. */
  83/* The Host publishes the avail index for which it expects a kick
  84 * at the end of the used ring. Guest should ignore the used->flags field. */
  85#define VIRTIO_RING_F_EVENT_IDX         29
  86
  87/* Alignment requirements for vring elements.
  88 * When using pre-virtio 1.0 layout, these fall out naturally.
  89 */
  90#define VRING_AVAIL_ALIGN_SIZE 2
  91#define VRING_USED_ALIGN_SIZE 4
  92#define VRING_DESC_ALIGN_SIZE 16
  93
  94/**
  95 * struct vring_desc - Virtio ring descriptors,
  96 * 16 bytes long. These can chain together via @next.
  97 *
  98 * @addr: buffer address (guest-physical)
  99 * @len: buffer length
 100 * @flags: descriptor flags
 101 * @next: index of the next descriptor in the chain,
 102 *        if the VRING_DESC_F_NEXT flag is set. We chain unused
 103 *        descriptors via this, too.
 104 */
 105struct vring_desc {
 106        __virtio64 addr;
 107        __virtio32 len;
 108        __virtio16 flags;
 109        __virtio16 next;
 110};
 111
 112struct vring_avail {
 113        __virtio16 flags;
 114        __virtio16 idx;
 115        __virtio16 ring[];
 116};
 117
 118/* uint32_t is used here for ids for padding reasons. */
 119struct vring_used_elem {
 120        /* Index of start of used descriptor chain. */
 121        __virtio32 id;
 122        /* Total length of the descriptor chain which was used (written to) */
 123        __virtio32 len;
 124};
 125
 126typedef struct vring_used_elem __attribute__((aligned(VRING_USED_ALIGN_SIZE)))
 127        vring_used_elem_t;
 128
 129struct vring_used {
 130        __virtio16 flags;
 131        __virtio16 idx;
 132        vring_used_elem_t ring[];
 133};
 134
 135/*
 136 * The ring element addresses are passed between components with different
 137 * alignments assumptions. Thus, we might need to decrease the compiler-selected
 138 * alignment, and so must use a typedef to make sure the aligned attribute
 139 * actually takes hold:
 140 *
 141 * https://gcc.gnu.org/onlinedocs//gcc/Common-Type-Attributes.html#Common-Type-Attributes
 142 *
 143 * When used on a struct, or struct member, the aligned attribute can only
 144 * increase the alignment; in order to decrease it, the packed attribute must
 145 * be specified as well. When used as part of a typedef, the aligned attribute
 146 * can both increase and decrease alignment, and specifying the packed
 147 * attribute generates a warning.
 148 */
 149typedef struct vring_desc __attribute__((aligned(VRING_DESC_ALIGN_SIZE)))
 150        vring_desc_t;
 151typedef struct vring_avail __attribute__((aligned(VRING_AVAIL_ALIGN_SIZE)))
 152        vring_avail_t;
 153typedef struct vring_used __attribute__((aligned(VRING_USED_ALIGN_SIZE)))
 154        vring_used_t;
 155
 156struct vring {
 157        unsigned int num;
 158
 159        vring_desc_t *desc;
 160
 161        vring_avail_t *avail;
 162
 163        vring_used_t *used;
 164};
 165
 166#ifndef VIRTIO_RING_NO_LEGACY
 167
 168/* The standard layout for the ring is a continuous chunk of memory which looks
 169 * like this.  We assume num is a power of 2.
 170 *
 171 * struct vring
 172 * {
 173 *      // The actual descriptors (16 bytes each)
 174 *      struct vring_desc desc[num];
 175 *
 176 *      // A ring of available descriptor heads with free-running index.
 177 *      __virtio16 avail_flags;
 178 *      __virtio16 avail_idx;
 179 *      __virtio16 available[num];
 180 *      __virtio16 used_event_idx;
 181 *
 182 *      // Padding to the next align boundary.
 183 *      char pad[];
 184 *
 185 *      // A ring of used descriptor heads with free-running index.
 186 *      __virtio16 used_flags;
 187 *      __virtio16 used_idx;
 188 *      struct vring_used_elem used[num];
 189 *      __virtio16 avail_event_idx;
 190 * };
 191 */
 192/* We publish the used event index at the end of the available ring, and vice
 193 * versa. They are at the end for backwards compatibility. */
 194#define vring_used_event(vr) ((vr)->avail->ring[(vr)->num])
 195#define vring_avail_event(vr) (*(__virtio16 *)&(vr)->used->ring[(vr)->num])
 196
 197static inline void vring_init(struct vring *vr, unsigned int num, void *p,
 198                              unsigned long align)
 199{
 200        vr->num = num;
 201        vr->desc = p;
 202        vr->avail = (struct vring_avail *)((char *)p + num * sizeof(struct vring_desc));
 203        vr->used = (void *)(((uintptr_t)&vr->avail->ring[num] + sizeof(__virtio16)
 204                + align-1) & ~(align - 1));
 205}
 206
 207static inline unsigned vring_size(unsigned int num, unsigned long align)
 208{
 209        return ((sizeof(struct vring_desc) * num + sizeof(__virtio16) * (3 + num)
 210                 + align - 1) & ~(align - 1))
 211                + sizeof(__virtio16) * 3 + sizeof(struct vring_used_elem) * num;
 212}
 213
 214#endif /* VIRTIO_RING_NO_LEGACY */
 215
 216/* The following is used with USED_EVENT_IDX and AVAIL_EVENT_IDX */
 217/* Assuming a given event_idx value from the other side, if
 218 * we have just incremented index from old to new_idx,
 219 * should we trigger an event? */
 220static inline int vring_need_event(uint16_t event_idx, uint16_t new_idx, uint16_t old)
 221{
 222        /* Note: Xen has similar logic for notification hold-off
 223         * in include/xen/interface/io/ring.h with req_event and req_prod
 224         * corresponding to event_idx + 1 and new_idx respectively.
 225         * Note also that req_event and req_prod in Xen start at 1,
 226         * event indexes in virtio start at 0. */
 227        return (uint16_t)(new_idx - event_idx - 1) < (uint16_t)(new_idx - old);
 228}
 229
 230struct vring_packed_desc_event {
 231        /* Descriptor Ring Change Event Offset/Wrap Counter. */
 232        uint16_t off_wrap;
 233        /* Descriptor Ring Change Event Flags. */
 234        uint16_t flags;
 235};
 236
 237struct vring_packed_desc {
 238        /* Buffer Address. */
 239        uint64_t addr;
 240        /* Buffer Length. */
 241        uint32_t len;
 242        /* Buffer ID. */
 243        uint16_t id;
 244        /* The flags depending on descriptor type. */
 245        uint16_t flags;
 246};
 247
 248#endif /* _LINUX_VIRTIO_RING_H */
 249