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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 * 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 <linux/types.h>
36#include <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". */
64struct 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
75struct vring_avail {
76 __virtio16 flags;
77 __virtio16 idx;
78 __virtio16 ring[];
79};
80
81/* u32 is used here for ids for padding reasons. */
82struct 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
89struct vring_used {
90 __virtio16 flags;
91 __virtio16 idx;
92 struct vring_used_elem ring[];
93};
94
95struct 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
141static __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
151static __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? */
162static __inline__ int vring_need_event(__u16 event_idx, __u16 new_idx, __u16 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 (__u16)(new_idx - event_idx - 1) < (__u16)(new_idx - old);
170}
171
172#endif /* _LINUX_VIRTIO_RING_H */
173

Warning: That file was not part of the compilation database. It may have many parsing errors.