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David Howells607ca462012-10-13 10:46:48 +01001#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>
Michael S. Tsirkineef960a02014-10-22 15:35:56 +030035#include <linux/virtio_types.h>
David Howells607ca462012-10-13 10:46:48 +010036
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". */
63struct vring_desc {
64 /* Address (guest-physical). */
Michael S. Tsirkineef960a02014-10-22 15:35:56 +030065 __virtio64 addr;
David Howells607ca462012-10-13 10:46:48 +010066 /* Length. */
Michael S. Tsirkineef960a02014-10-22 15:35:56 +030067 __virtio32 len;
David Howells607ca462012-10-13 10:46:48 +010068 /* The flags as indicated above. */
Michael S. Tsirkineef960a02014-10-22 15:35:56 +030069 __virtio16 flags;
David Howells607ca462012-10-13 10:46:48 +010070 /* We chain unused descriptors via this, too */
Michael S. Tsirkineef960a02014-10-22 15:35:56 +030071 __virtio16 next;
David Howells607ca462012-10-13 10:46:48 +010072};
73
74struct vring_avail {
Michael S. Tsirkineef960a02014-10-22 15:35:56 +030075 __virtio16 flags;
76 __virtio16 idx;
77 __virtio16 ring[];
David Howells607ca462012-10-13 10:46:48 +010078};
79
80/* u32 is used here for ids for padding reasons. */
81struct vring_used_elem {
82 /* Index of start of used descriptor chain. */
Michael S. Tsirkineef960a02014-10-22 15:35:56 +030083 __virtio32 id;
David Howells607ca462012-10-13 10:46:48 +010084 /* Total length of the descriptor chain which was used (written to) */
Michael S. Tsirkineef960a02014-10-22 15:35:56 +030085 __virtio32 len;
David Howells607ca462012-10-13 10:46:48 +010086};
87
88struct vring_used {
Michael S. Tsirkineef960a02014-10-22 15:35:56 +030089 __virtio16 flags;
90 __virtio16 idx;
David Howells607ca462012-10-13 10:46:48 +010091 struct vring_used_elem ring[];
92};
93
94struct 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
Michael S. Tsirkinb28e0502014-12-25 16:03:27 +0200104/* 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
David Howells607ca462012-10-13 10:46:48 +0100111/* 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.
Michael S. Tsirkineef960a02014-10-22 15:35:56 +0300120 * __virtio16 avail_flags;
121 * __virtio16 avail_idx;
122 * __virtio16 available[num];
123 * __virtio16 used_event_idx;
David Howells607ca462012-10-13 10:46:48 +0100124 *
125 * // Padding to the next align boundary.
126 * char pad[];
127 *
128 * // A ring of used descriptor heads with free-running index.
Michael S. Tsirkineef960a02014-10-22 15:35:56 +0300129 * __virtio16 used_flags;
130 * __virtio16 used_idx;
David Howells607ca462012-10-13 10:46:48 +0100131 * struct vring_used_elem used[num];
Michael S. Tsirkineef960a02014-10-22 15:35:56 +0300132 * __virtio16 avail_event_idx;
David Howells607ca462012-10-13 10:46:48 +0100133 * };
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])
Michael S. Tsirkineef960a02014-10-22 15:35:56 +0300138#define vring_avail_event(vr) (*(__virtio16 *)&(vr)->used->ring[(vr)->num])
David Howells607ca462012-10-13 10:46:48 +0100139
140static 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);
Michael S. Tsirkineef960a02014-10-22 15:35:56 +0300146 vr->used = (void *)(((unsigned long)&vr->avail->ring[num] + sizeof(__virtio16)
David Howells607ca462012-10-13 10:46:48 +0100147 + align-1) & ~(align - 1));
148}
149
150static inline unsigned vring_size(unsigned int num, unsigned long align)
151{
Michael S. Tsirkineef960a02014-10-22 15:35:56 +0300152 return ((sizeof(struct vring_desc) * num + sizeof(__virtio16) * (3 + num)
David Howells607ca462012-10-13 10:46:48 +0100153 + align - 1) & ~(align - 1))
Michael S. Tsirkineef960a02014-10-22 15:35:56 +0300154 + sizeof(__virtio16) * 3 + sizeof(struct vring_used_elem) * num;
David Howells607ca462012-10-13 10:46:48 +0100155}
156
157/* The following is used with USED_EVENT_IDX and AVAIL_EVENT_IDX */
Stefan Hajnoczie412d3a2015-05-02 08:42:29 +0930158/* Assuming a given event_idx value from the other side, if
David Howells607ca462012-10-13 10:46:48 +0100159 * we have just incremented index from old to new_idx,
160 * should we trigger an event? */
161static 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 */