include/hw/virtio/virtio_ring.h

   1 #ifndef _LINUX_VIRTIO_RING_H
   2 #define _LINUX_VIRTIO_RING_H
   3 /*
   4  * This file is copied from /usr/include/linux while converting __uNN types
   5  * to uXX_t, __inline__ to inline, and tab to spaces.
   6  * */
   7
   8 /* An interface for efficient virtio implementation, currently for use by KVM
   9  * and lguest, but hopefully others soon.  Do NOT change this since it will
  10  * break existing servers and clients.
  11  *
  12  * This header is BSD licensed so anyone can use the definitions to implement
  13  * compatible drivers/servers.
  14  *
  15  * Redistribution and use in source and binary forms, with or without
  16  * modification, are permitted provided that the following conditions
  17  * are met:
  18  * 1. Redistributions of source code must retain the above copyright
  19  *    notice, this list of conditions and the following disclaimer.
  20  * 2. Redistributions in binary form must reproduce the above copyright
  21  *    notice, this list of conditions and the following disclaimer in the
  22  *    documentation and/or other materials provided with the distribution.
  23  * 3. Neither the name of IBM nor the names of its contributors
  24  *    may be used to endorse or promote products derived from this software
  25  *    without specific prior written permission.
  26  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS ``AS IS'' AND
  27  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  28  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  29  * ARE DISCLAIMED.  IN NO EVENT SHALL IBM OR CONTRIBUTORS BE LIABLE
  30  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  31  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  32  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  33  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  34  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  35  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  36  * SUCH DAMAGE.
  37  *
  38  * Copyright Rusty Russell IBM Corporation 2007. */
  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". */
  66 struct vring_desc {
  67     /* Address (guest-physical). */
  68     uint64_t addr;
  69     /* Length. */
  70     uint32_t len;
  71     /* The flags as indicated above. */
  72     uint16_t flags;
  73     /* We chain unused descriptors via this, too */
  74     uint16_t next;
  75 };
  76
  77 struct vring_avail {
  78     uint16_t flags;
  79     uint16_t idx;
  80     uint16_t ring[];
  81 };
  82
  83 /* u32 is used here for ids for padding reasons. */
  84 struct vring_used_elem {
  85     /* Index of start of used descriptor chain. */
  86     uint32_t id;
  87     /* Total length of the descriptor chain which was used (written to) */
  88     uint32_t len;
  89 };
  90
  91 struct vring_used {
  92     uint16_t flags;
  93     uint16_t idx;
  94     struct vring_used_elem ring[];
  95 };
  96
  97 struct 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 /* The standard layout for the ring is a continuous chunk of memory which looks
 108  * like this.  We assume num is a power of 2.
 109  *
 110  * struct vring
 111  * {
 112  *  // The actual descriptors (16 bytes each)
 113  *  struct vring_desc desc[num];
 114  *
 115  *  // A ring of available descriptor heads with free-running index.
 116  *  uint16_t avail_flags;
 117  *  uint16_t avail_idx;
 118  *  uint16_t available[num];
 119  *  uint16_t used_event_idx;
 120  *
 121  *  // Padding to the next align boundary.
 122  *  char pad[];
 123  *
 124  *  // A ring of used descriptor heads with free-running index.
 125  *  uint16_t used_flags;
 126  *  uint16_t used_idx;
 127  *  struct vring_used_elem used[num];
 128  *  uint16_t avail_event_idx;
 129  * };
 130  */
 131 /* We publish the used event index at the end of the available ring, and vice
 132  * versa. They are at the end for backwards compatibility. */
 133 #define vring_used_event(vr) ((vr)->avail->ring[(vr)->num])
 134 #define vring_avail_event(vr) (*(uint16_t *)&(vr)->used->ring[(vr)->num])
 135
 136 static inline void vring_init(struct vring *vr, unsigned int num, void *p,
 137                   unsigned long align)
 138 {
 139     vr->num = num;
 140     vr->desc = p;
 141     vr->avail = p + num*sizeof(struct vring_desc);
 142     vr->used = (void *)(((unsigned long)&vr->avail->ring[num] + sizeof(uint16_t)
 143         + align-1) & ~(align - 1));
 144 }
 145
 146 static inline unsigned vring_size(unsigned int num, unsigned long align)
 147 {
 148     return ((sizeof(struct vring_desc) * num + sizeof(uint16_t) * (3 + num)
 149          + align - 1) & ~(align - 1))
 150         + sizeof(uint16_t) * 3 + sizeof(struct vring_used_elem) * num;
 151 }
 152
 153 /* The following is used with USED_EVENT_IDX and AVAIL_EVENT_IDX */
 154 /* Assuming a given event_idx value from the other size, if
 155  * we have just incremented index from old to new_idx,
 156  * should we trigger an event? */
 157 static inline int vring_need_event(uint16_t event_idx, uint16_t new_idx, uint16_t old)
 158 {
 159     /* Note: Xen has similar logic for notification hold-off
 160      * in include/xen/interface/io/ring.h with req_event and req_prod
 161      * corresponding to event_idx + 1 and new_idx respectively.
 162      * Note also that req_event and req_prod in Xen start at 1,
 163      * event indexes in virtio start at 0. */
 164     return (uint16_t)(new_idx - event_idx - 1) < (uint16_t)(new_idx - old);
 165 }
 166
 167 #endif /* _LINUX_VIRTIO_RING_H */