include/uapi/linux/virtio_ring.h

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