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  * 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 /*
  48  * Mark a descriptor as available or used in packed ring.
  49  * Notice: they are defined as shifts instead of shifted values.
  50  */
  51 #define VRING_PACKED_DESC_F_AVAIL       7
  52 #define VRING_PACKED_DESC_F_USED        15
  53
  54 /* The Host uses this in used->flags to advise the Guest: don't kick me when
  55  * you add a buffer.  It's unreliable, so it's simply an optimization.  Guest
  56  * will still kick if it's out of buffers. */
  57 #define VRING_USED_F_NO_NOTIFY  1
  58 /* The Guest uses this in avail->flags to advise the Host: don't interrupt me
  59  * when you consume a buffer.  It's unreliable, so it's simply an
  60  * optimization.  */
  61 #define VRING_AVAIL_F_NO_INTERRUPT      1
  62
  63 /* Enable events in packed ring. */
  64 #define VRING_PACKED_EVENT_FLAG_ENABLE  0x0
  65 /* Disable events in packed ring. */
  66 #define VRING_PACKED_EVENT_FLAG_DISABLE 0x1
  67 /*
  68  * Enable events for a specific descriptor in packed ring.
  69  * (as specified by Descriptor Ring Change Event Offset/Wrap Counter).
  70  * Only valid if VIRTIO_RING_F_EVENT_IDX has been negotiated.
  71  */
  72 #define VRING_PACKED_EVENT_FLAG_DESC    0x2
  73
  74 /*
  75  * Wrap counter bit shift in event suppression structure
  76  * of packed ring.
  77  */
  78 #define VRING_PACKED_EVENT_F_WRAP_CTR   15
  79
  80 /* We support indirect buffer descriptors */
  81 #define VIRTIO_RING_F_INDIRECT_DESC     28
  82
  83 /* The Guest publishes the used index for which it expects an interrupt
  84  * at the end of the avail ring. Host should ignore the avail->flags field. */
  85 /* The Host publishes the avail index for which it expects a kick
  86  * at the end of the used ring. Guest should ignore the used->flags field. */
  87 #define VIRTIO_RING_F_EVENT_IDX         29
  88
  89 /* Virtio ring descriptors: 16 bytes.  These can chain together via "next". */
  90 struct vring_desc {
  91         /* Address (guest-physical). */
  92         __virtio64 addr;
  93         /* Length. */
  94         __virtio32 len;
  95         /* The flags as indicated above. */
  96         __virtio16 flags;
  97         /* We chain unused descriptors via this, too */
  98         __virtio16 next;
  99 };
 100
 101 struct vring_avail {
 102         __virtio16 flags;
 103         __virtio16 idx;
 104         __virtio16 ring[];
 105 };
 106
 107 /* u32 is used here for ids for padding reasons. */
 108 struct vring_used_elem {
 109         /* Index of start of used descriptor chain. */
 110         __virtio32 id;
 111         /* Total length of the descriptor chain which was used (written to) */
 112         __virtio32 len;
 113 };
 114
 115 struct vring_used {
 116         __virtio16 flags;
 117         __virtio16 idx;
 118         struct vring_used_elem ring[];
 119 };
 120
 121 struct vring {
 122         unsigned int num;
 123
 124         struct vring_desc *desc;
 125
 126         struct vring_avail *avail;
 127
 128         struct vring_used *used;
 129 };
 130
 131 /* Alignment requirements for vring elements.
 132  * When using pre-virtio 1.0 layout, these fall out naturally.
 133  */
 134 #define VRING_AVAIL_ALIGN_SIZE 2
 135 #define VRING_USED_ALIGN_SIZE 4
 136 #define VRING_DESC_ALIGN_SIZE 16
 137
 138 /* The standard layout for the ring is a continuous chunk of memory which looks
 139  * like this.  We assume num is a power of 2.
 140  *
 141  * struct vring
 142  * {
 143  *      // The actual descriptors (16 bytes each)
 144  *      struct vring_desc desc[num];
 145  *
 146  *      // A ring of available descriptor heads with free-running index.
 147  *      __virtio16 avail_flags;
 148  *      __virtio16 avail_idx;
 149  *      __virtio16 available[num];
 150  *      __virtio16 used_event_idx;
 151  *
 152  *      // Padding to the next align boundary.
 153  *      char pad[];
 154  *
 155  *      // A ring of used descriptor heads with free-running index.
 156  *      __virtio16 used_flags;
 157  *      __virtio16 used_idx;
 158  *      struct vring_used_elem used[num];
 159  *      __virtio16 avail_event_idx;
 160  * };
 161  */
 162 /* We publish the used event index at the end of the available ring, and vice
 163  * versa. They are at the end for backwards compatibility. */
 164 #define vring_used_event(vr) ((vr)->avail->ring[(vr)->num])
 165 #define vring_avail_event(vr) (*(__virtio16 *)&(vr)->used->ring[(vr)->num])
 166
 167 static inline void vring_init(struct vring *vr, unsigned int num, void *p,
 168                               unsigned long align)
 169 {
 170         vr->num = num;
 171         vr->desc = p;
 172         vr->avail = p + num*sizeof(struct vring_desc);
 173         vr->used = (void *)(((uintptr_t)&vr->avail->ring[num] + sizeof(__virtio16)
 174                 + align-1) & ~(align - 1));
 175 }
 176
 177 static inline unsigned vring_size(unsigned int num, unsigned long align)
 178 {
 179         return ((sizeof(struct vring_desc) * num + sizeof(__virtio16) * (3 + num)
 180                  + align - 1) & ~(align - 1))
 181                 + sizeof(__virtio16) * 3 + sizeof(struct vring_used_elem) * num;
 182 }
 183
 184 /* The following is used with USED_EVENT_IDX and AVAIL_EVENT_IDX */
 185 /* Assuming a given event_idx value from the other side, if
 186  * we have just incremented index from old to new_idx,
 187  * should we trigger an event? */
 188 static inline int vring_need_event(__u16 event_idx, __u16 new_idx, __u16 old)
 189 {
 190         /* Note: Xen has similar logic for notification hold-off
 191          * in include/xen/interface/io/ring.h with req_event and req_prod
 192          * corresponding to event_idx + 1 and new_idx respectively.
 193          * Note also that req_event and req_prod in Xen start at 1,
 194          * event indexes in virtio start at 0. */
 195         return (__u16)(new_idx - event_idx - 1) < (__u16)(new_idx - old);
 196 }
 197
 198 struct vring_packed_desc_event {
 199         /* Descriptor Ring Change Event Offset/Wrap Counter. */
 200         __le16 off_wrap;
 201         /* Descriptor Ring Change Event Flags. */
 202         __le16 flags;
 203 };
 204
 205 struct vring_packed_desc {
 206         /* Buffer Address. */
 207         __le64 addr;
 208         /* Buffer Length. */
 209         __le32 len;
 210         /* Buffer ID. */
 211         __le16 id;
 212         /* The flags depending on descriptor type. */
 213         __le16 flags;
 214 };
 215
 216 struct vring_packed {
 217         unsigned int num;
 218
 219         struct vring_packed_desc *desc;
 220
 221         struct vring_packed_desc_event *driver;
 222
 223         struct vring_packed_desc_event *device;
 224 };
 225
 226 #endif /* _UAPI_LINUX_VIRTIO_RING_H */