2 * Copyright Rusty Russell IBM Corporation 2007.
4 * This header is BSD licensed so anyone can use the definitions to implement
5 * compatible drivers/servers.
7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that the following conditions
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)
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27 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
30 * $FreeBSD: src/sys/dev/virtio/virtio_ring.h,v 1.3 2012/04/14 05:48:04 grehan Exp $
36 #include <sys/types.h>
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 /* 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.
99 * // The actual descriptors (16 bytes each)
100 * struct vring_desc desc[num];
102 * // A ring of available descriptor heads with free-running index.
105 * __u16 available[num];
106 * __u16 used_event_idx;
108 * // Padding to the next align boundary.
111 * // A ring of used descriptor heads with free-running index.
114 * struct vring_used_elem used[num];
115 * __u16 avail_event_idx;
118 * NOTE: for VirtIO PCI, align is 4096.
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.
125 #define vring_used_event(vr) ((vr)->avail->ring[(vr)->num])
126 #define vring_avail_event(vr) (*(uint16_t *)&(vr)->used->ring[(vr)->num])
129 vring_size(unsigned int num, unsigned long align)
133 size = num * sizeof(struct vring_desc);
134 size += sizeof(struct vring_avail) + (num * sizeof(uint16_t));
135 size = roundup2(size, align);
136 size += sizeof(struct vring_used) +
137 (num * sizeof(struct vring_used_elem));
142 vring_init(struct vring *vr, unsigned int num, uint8_t *p,
146 vr->desc = (struct vring_desc *) p;
147 vr->avail = (struct vring_avail *) (p +
148 num * sizeof(struct vring_desc));
150 (void *)roundup2((unsigned long)&vr->avail->ring[num], align);
154 * The following is used with VIRTIO_RING_F_EVENT_IDX.
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
161 vring_need_event(uint16_t event_idx, uint16_t new_idx, uint16_t old)
164 return (uint16_t)(new_idx - event_idx - 1) < (uint16_t)(new_idx - old);
166 #endif /* VIRTIO_RING_H */