2 * SPDX-License-Identifier: BSD-3-Clause
4 * Copyright Rusty Russell IBM Corporation 2007.
6 * This header is BSD licensed so anyone can use the definitions to implement
7 * compatible drivers/servers.
9 * Redistribution and use in source and binary forms, with or without
10 * modification, are permitted provided that the following conditions
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)
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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
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
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
54 /* VirtIO ring descriptors: 16 bytes.
55 * These can chain together via "next". */
57 /* Address (guest-physical). */
61 /* The flags as indicated above. */
63 /* We chain unused descriptors via this, too. */
73 /* uint32_t is used here for ids for padding reasons. */
74 struct vring_used_elem {
75 /* Index of start of used descriptor chain. */
77 /* Total length of the descriptor chain which was written to. */
84 struct vring_used_elem ring[0];
90 struct vring_desc *desc;
91 struct vring_avail *avail;
92 struct vring_used *used;
95 /* Alignment requirements for vring elements.
96 * When using pre-virtio 1.0 layout, these fall out naturally.
98 #define VRING_AVAIL_ALIGN_SIZE 2
99 #define VRING_USED_ALIGN_SIZE 4
100 #define VRING_DESC_ALIGN_SIZE 16
102 /* The standard layout for the ring is a continuous chunk of memory which
103 * looks like this. We assume num is a power of 2.
106 * // The actual descriptors (16 bytes each)
107 * struct vring_desc desc[num];
109 * // A ring of available descriptor heads with free-running index.
112 * __u16 available[num];
113 * __u16 used_event_idx;
115 * // Padding to the next align boundary.
118 * // A ring of used descriptor heads with free-running index.
121 * struct vring_used_elem used[num];
122 * __u16 avail_event_idx;
125 * NOTE: for VirtIO PCI, align is 4096.
129 * We publish the used event index at the end of the available ring, and vice
130 * versa. They are at the end for backwards compatibility.
132 #define vring_used_event(vr) ((vr)->avail->ring[(vr)->num])
133 #define vring_avail_event(vr) (*(uint16_t *)&(vr)->used->ring[(vr)->num])
136 vring_size(unsigned int num, unsigned long align)
140 size = num * sizeof(struct vring_desc);
141 size += sizeof(struct vring_avail) + (num * sizeof(uint16_t)) +
143 size = (size + align - 1) & ~(align - 1);
144 size += sizeof(struct vring_used) +
145 (num * sizeof(struct vring_used_elem)) + sizeof(uint16_t);
150 vring_init(struct vring *vr, unsigned int num, uint8_t *p,
154 vr->desc = (struct vring_desc *) p;
155 vr->avail = (struct vring_avail *) (p +
156 num * sizeof(struct vring_desc));
158 (((unsigned long) &vr->avail->ring[num] + align-1) & ~(align-1));
162 * The following is used with VIRTIO_RING_F_EVENT_IDX.
164 * Assuming a given event_idx value from the other size, if we have
165 * just incremented index from old to new_idx, should we trigger an
169 vring_need_event(uint16_t event_idx, uint16_t new_idx, uint16_t old)
172 return (uint16_t)(new_idx - event_idx - 1) < (uint16_t)(new_idx - old);
174 #endif /* VIRTIO_RING_H */