include/standard-headers/linux/virtio_ring.h

   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  * 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 <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". */
  64 struct 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
  75 struct vring_avail {
  76         __virtio16 flags;
  77         __virtio16 idx;
  78         __virtio16 ring[];
  79 };
  80
  81 /* u32 is used here for ids for padding reasons. */
  82 struct 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
  89 struct vring_used {
  90         __virtio16 flags;
  91         __virtio16 idx;
  92         struct vring_used_elem ring[];
  93 };
  94
  95 struct 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
 141 static 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
 151 static 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? */
 162 static 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 */