virtio_ring.h revision 234270 
1/*-
2 * Copyright Rusty Russell IBM Corporation 2007.
3 *
4 * This header is BSD licensed so anyone can use the definitions to implement
5 * compatible drivers/servers.
6 *
7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that the following conditions
9 * are met:
10 * 1. Redistributions of source code must retain the above copyright
11 *    notice, this list of conditions and the following disclaimer.
12 * 2. Redistributions in binary form must reproduce the above copyright
13 *    notice, this list of conditions and the following disclaimer in the
14 *    documentation and/or other materials provided with the distribution.
15 * 3. Neither the name of IBM nor the names of its contributors
16 *    may be used to endorse or promote products derived from this software
17 *    without specific prior written permission.
18 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
19 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
20 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
21 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL IBM OR CONTRIBUTORS BE LIABLE
22 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
23 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
24 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
25 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
26 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
27 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
28 * SUCH DAMAGE.
29 *
30 * $FreeBSD: head/sys/dev/virtio/virtio_ring.h 234270 2012-04-14 05:48:04Z grehan $
31 */
32
33#ifndef VIRTIO_RING_H
34#define	VIRTIO_RING_H
35
36#include <sys/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
46 * when you add a buffer.  It's unreliable, so it's simply an
47 * optimization.  Guest 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
50 * interrupt me when you consume a buffer.  It's unreliable, so it's
51 * simply an optimization.  */
52#define VRING_AVAIL_F_NO_INTERRUPT      1
53
54/* VirtIO ring descriptors: 16 bytes.
55 * These can chain together via "next". */
56struct vring_desc {
57        /* Address (guest-physical). */
58        uint64_t addr;
59        /* Length. */
60        uint32_t len;
61        /* The flags as indicated above. */
62        uint16_t flags;
63        /* We chain unused descriptors via this, too. */
64        uint16_t next;
65};
66
67struct vring_avail {
68        uint16_t flags;
69        uint16_t idx;
70        uint16_t ring[0];
71};
72
73/* uint32_t is used here for ids for padding reasons. */
74struct vring_used_elem {
75        /* Index of start of used descriptor chain. */
76        uint32_t id;
77        /* Total length of the descriptor chain which was written to. */
78        uint32_t len;
79};
80
81struct vring_used {
82        uint16_t flags;
83        uint16_t idx;
84        struct vring_used_elem ring[0];
85};
86
87struct vring {
88	unsigned int num;
89
90	struct vring_desc *desc;
91	struct vring_avail *avail;
92	struct vring_used *used;
93};
94
95/* The standard layout for the ring is a continuous chunk of memory which
96 * looks like this.  We assume num is a power of 2.
97 *
98 * struct vring {
99 *      // The actual descriptors (16 bytes each)
100 *      struct vring_desc desc[num];
101 *
102 *      // A ring of available descriptor heads with free-running index.
103 *      __u16 avail_flags;
104 *      __u16 avail_idx;
105 *      __u16 available[num];
106 *      __u16 used_event_idx;
107 *
108 *      // Padding to the next align boundary.
109 *      char pad[];
110 *
111 *      // A ring of used descriptor heads with free-running index.
112 *      __u16 used_flags;
113 *      __u16 used_idx;
114 *      struct vring_used_elem used[num];
115 *      __u16 avail_event_idx;
116 * };
117 *
118 * NOTE: for VirtIO PCI, align is 4096.
119 */
120
121/*
122 * We publish the used event index at the end of the available ring, and vice
123 * versa. They are at the end for backwards compatibility.
124 */
125#define	vring_used_event(vr)	((vr)->avail->ring[(vr)->num])
126#define	vring_avail_event(vr)	(*(uint16_t *)&(vr)->used->ring[(vr)->num])
127
128static inline int
129vring_size(unsigned int num, unsigned long align)
130{
131	int size;
132
133	size = num * sizeof(struct vring_desc);
134	size += sizeof(struct vring_avail) + (num * sizeof(uint16_t));
135	size = (size + align - 1) & ~(align - 1);
136	size += sizeof(struct vring_used) +
137	    (num * sizeof(struct vring_used_elem));
138	return (size);
139}
140
141static inline void
142vring_init(struct vring *vr, unsigned int num, uint8_t *p,
143    unsigned long align)
144{
145        vr->num = num;
146        vr->desc = (struct vring_desc *) p;
147        vr->avail = (struct vring_avail *) (p +
148	    num * sizeof(struct vring_desc));
149        vr->used = (void *)
150	    (((unsigned long) &vr->avail->ring[num] + align-1) & ~(align-1));
151}
152
153/*
154 * The following is used with VIRTIO_RING_F_EVENT_IDX.
155 *
156 * Assuming a given event_idx value from the other size, if we have
157 * just incremented index from old to new_idx, should we trigger an
158 * event?
159 */
160static inline int
161vring_need_event(uint16_t event_idx, uint16_t new_idx, uint16_t old)
162{
163
164	return (uint16_t)(new_idx - event_idx - 1) < (uint16_t)(new_idx - old);
165}
166#endif /* VIRTIO_RING_H */
167