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". */
54struct 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
65struct 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. */
72struct 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
79struct vring_used {
80        uint16_t flags;
81        uint16_t idx;
82        struct vring_used_elem ring[0];
83};
84
85struct 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
133static inline int
134vring_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
147static inline void
148vring_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 */
166static inline int
167vring_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