1 /*-
2 * SPDX-License-Identifier: BSD-3-Clause
3 *
4 * Copyright Rusty Russell IBM Corporation 2007.
5 *
6 * This header is BSD licensed so anyone can use the definitions to implement
7 * compatible drivers/servers.
8 *
9 * Redistribution and use in source and binary forms, with or without
10 * modification, are permitted provided that the following conditions
11 * are met:
12 * 1. Redistributions of source code must retain the above copyright
13 * notice, this list of conditions and the following disclaimer.
14 * 2. Redistributions in binary form must reproduce the above copyright
15 * notice, this list of conditions and the following disclaimer in the
16 * documentation and/or other materials provided with the distribution.
17 * 3. Neither the name of IBM nor the names of its contributors
18 * may be used to endorse or promote products derived from this software
19 * without specific prior written permission.
20 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
21 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
22 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
23 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL IBM OR CONTRIBUTORS BE LIABLE
24 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
25 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
26 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
27 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
28 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
29 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
30 * SUCH DAMAGE.
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 /* Alignment requirements for vring elements.
94 * When using pre-virtio 1.0 layout, these fall out naturally.
95 */
96 #define VRING_AVAIL_ALIGN_SIZE 2
97 #define VRING_USED_ALIGN_SIZE 4
98 #define VRING_DESC_ALIGN_SIZE 16
99
100 /* The standard layout for the ring is a continuous chunk of memory which
101 * looks like this. We assume num is a power of 2.
102 *
103 * struct vring {
104 * // The actual descriptors (16 bytes each)
105 * struct vring_desc desc[num];
106 *
107 * // A ring of available descriptor heads with free-running index.
108 * __u16 avail_flags;
109 * __u16 avail_idx;
110 * __u16 available[num];
111 * __u16 used_event_idx;
112 *
113 * // Padding to the next align boundary.
114 * char pad[];
115 *
116 * // A ring of used descriptor heads with free-running index.
117 * __u16 used_flags;
118 * __u16 used_idx;
119 * struct vring_used_elem used[num];
120 * __u16 avail_event_idx;
121 * };
122 *
123 * NOTE: for VirtIO PCI, align is 4096.
124 */
125
126 /*
127 * We publish the used event index at the end of the available ring, and vice
128 * versa. They are at the end for backwards compatibility.
129 */
130 #define vring_used_event(vr) ((vr)->avail->ring[(vr)->num])
131 #define vring_avail_event(vr) (*(uint16_t *)&(vr)->used->ring[(vr)->num])
132
133 static inline int
vring_size(unsigned int num,unsigned long align)134 vring_size(unsigned int num, unsigned long align)
135 {
136 int size;
137
138 size = num * sizeof(struct vring_desc);
139 size += sizeof(struct vring_avail) + (num * sizeof(uint16_t)) +
140 sizeof(uint16_t);
141 size = (size + align - 1) & ~(align - 1);
142 size += sizeof(struct vring_used) +
143 (num * sizeof(struct vring_used_elem)) + sizeof(uint16_t);
144 return (size);
145 }
146
147 static inline void
vring_init(struct vring * vr,unsigned int num,uint8_t * p,unsigned long align)148 vring_init(struct vring *vr, unsigned int num, uint8_t *p,
149 unsigned long align)
150 {
151 vr->num = num;
152 vr->desc = (struct vring_desc *) p;
153 vr->avail = (struct vring_avail *) (p +
154 num * sizeof(struct vring_desc));
155 vr->used = (void *)
156 (((unsigned long) &vr->avail->ring[num] + align-1) & ~(align-1));
157 }
158
159 /*
160 * The following is used with VIRTIO_RING_F_EVENT_IDX.
161 *
162 * Assuming a given event_idx value from the other size, if we have
163 * just incremented index from old to new_idx, should we trigger an
164 * event?
165 */
166 static inline int
vring_need_event(uint16_t event_idx,uint16_t new_idx,uint16_t old)167 vring_need_event(uint16_t event_idx, uint16_t new_idx, uint16_t old)
168 {
169
170 return (uint16_t)(new_idx - event_idx - 1) < (uint16_t)(new_idx - old);
171 }
172 #endif /* VIRTIO_RING_H */
173