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 * $FreeBSD$
31 */
32
33 #ifndef VIRTIO_RING_H
34 #define VIRTIO_RING_H
35
36 /* This marks a buffer as continuing via the next field. */
37 #define VRING_DESC_F_NEXT 1
38 /* This marks a buffer as write-only (otherwise read-only). */
39 #define VRING_DESC_F_WRITE 2
40 /* This means the buffer contains a list of buffer descriptors. */
41 #define VRING_DESC_F_INDIRECT 4
42
43 /* The Host uses this in used->flags to advise the Guest: don't kick me
44 * when you add a buffer. It's unreliable, so it's simply an
45 * optimization. Guest will still kick if it's out of buffers. */
46 #define VRING_USED_F_NO_NOTIFY 1
47 /* The Guest uses this in avail->flags to advise the Host: don't
48 * interrupt me when you consume a buffer. It's unreliable, so it's
49 * simply an optimization. */
50 #define VRING_AVAIL_F_NO_INTERRUPT 1
51
52 /* VirtIO ring descriptors: 16 bytes.
53 * These can chain together via "next". */
54 struct vring_desc {
55 /* Address (guest-physical). */
56 uint64_t addr;
57 /* Length. */
58 uint32_t len;
59 /* The flags as indicated above. */
60 uint16_t flags;
61 /* We chain unused descriptors via this, too. */
62 uint16_t next;
63 };
64
65 struct vring_avail {
66 uint16_t flags;
67 uint16_t idx;
68 uint16_t ring[0];
69 };
70
71 /* uint32_t is used here for ids for padding reasons. */
72 struct vring_used_elem {
73 /* Index of start of used descriptor chain. */
74 uint32_t id;
75 /* Total length of the descriptor chain which was written to. */
76 uint32_t len;
77 };
78
79 struct vring_used {
80 uint16_t flags;
81 uint16_t idx;
82 struct vring_used_elem ring[0];
83 };
84
85 struct vring {
86 unsigned int num;
87
88 struct vring_desc *desc;
89 struct vring_avail *avail;
90 struct vring_used *used;
91 };
92
93 /* The standard layout for the ring is a continuous chunk of memory which
94 * looks like this. We assume num is a power of 2.
95 *
96 * struct vring {
97 * // The actual descriptors (16 bytes each)
98 * struct vring_desc desc[num];
99 *
100 * // A ring of available descriptor heads with free-running index.
101 * __u16 avail_flags;
102 * __u16 avail_idx;
103 * __u16 available[num];
104 * __u16 used_event_idx;
105 *
106 * // Padding to the next align boundary.
107 * char pad[];
108 *
109 * // A ring of used descriptor heads with free-running index.
110 * __u16 used_flags;
111 * __u16 used_idx;
112 * struct vring_used_elem used[num];
113 * __u16 avail_event_idx;
114 * };
115 *
116 * NOTE: for VirtIO PCI, align is 4096.
117 */
118
119 /*
120 * We publish the used event index at the end of the available ring, and vice
121 * versa. They are at the end for backwards compatibility.
122 */
123 #define vring_used_event(vr) ((vr)->avail->ring[(vr)->num])
124 #define vring_avail_event(vr) (*(uint16_t *)&(vr)->used->ring[(vr)->num])
125
126 static inline int
vring_size(unsigned int num,unsigned long align)127 vring_size(unsigned int num, unsigned long align)
128 {
129 int size;
130
131 size = num * sizeof(struct vring_desc);
132 size += sizeof(struct vring_avail) + (num * sizeof(uint16_t)) +
133 sizeof(uint16_t);
134 size = (size + align - 1) & ~(align - 1);
135 size += sizeof(struct vring_used) +
136 (num * sizeof(struct vring_used_elem)) + sizeof(uint16_t);
137 return (size);
138 }
139
140 static inline void
vring_init(struct vring * vr,unsigned int num,uint8_t * p,unsigned long align)141 vring_init(struct vring *vr, unsigned int num, uint8_t *p,
142 unsigned long align)
143 {
144 vr->num = num;
145 vr->desc = (struct vring_desc *) p;
146 vr->avail = (struct vring_avail *) (p +
147 num * sizeof(struct vring_desc));
148 vr->used = (struct vring_used *)
149 (((addr_t) &vr->avail->ring[num] + align-1) & ~(align-1));
150 }
151
152 /*
153 * The following is used with VIRTIO_RING_F_EVENT_IDX.
154 *
155 * Assuming a given event_idx value from the other size, if we have
156 * just incremented index from old to new_idx, should we trigger an
157 * event?
158 */
159 static inline int
vring_need_event(uint16_t event_idx,uint16_t new_idx,uint16_t old)160 vring_need_event(uint16_t event_idx, uint16_t new_idx, uint16_t old)
161 {
162
163 return (uint16_t)(new_idx - event_idx - 1) < (uint16_t)(new_idx - old);
164 }
165 #endif /* VIRTIO_RING_H */
166