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)
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
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
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
52 /* VirtIO ring descriptors: 16 bytes.
53 * These can chain together via "next". */
55 /* Address (guest-physical). */
59 /* The flags as indicated above. */
61 /* We chain unused descriptors via this, too. */
71 /* uint32_t is used here for ids for padding reasons. */
72 struct vring_used_elem {
73 /* Index of start of used descriptor chain. */
75 /* Total length of the descriptor chain which was written to. */
82 struct vring_used_elem ring[0];
88 struct vring_desc *desc;
89 struct vring_avail *avail;
90 struct vring_used *used;
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.
97 * // The actual descriptors (16 bytes each)
98 * struct vring_desc desc[num];
100 * // A ring of available descriptor heads with free-running index.
103 * __u16 available[num];
104 * __u16 used_event_idx;
106 * // Padding to the next align boundary.
109 * // A ring of used descriptor heads with free-running index.
112 * struct vring_used_elem used[num];
113 * __u16 avail_event_idx;
116 * NOTE: for VirtIO PCI, align is 4096.
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.
123 #define vring_used_event(vr) ((vr)->avail->ring[(vr)->num])
124 #define vring_avail_event(vr) (*(uint16_t *)&(vr)->used->ring[(vr)->num])
127 vring_size(unsigned int num, unsigned long align)
131 size = num * sizeof(struct vring_desc);
132 size += sizeof(struct vring_avail) + (num * 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);
141 vring_init(struct vring *vr, unsigned int num, uint8_t *p,
145 vr->desc = (struct vring_desc *) p;
146 vr->avail = (struct vring_avail *) (p +
147 num * sizeof(struct vring_desc));
149 (((unsigned long) &vr->avail->ring[num] + align-1) & ~(align-1));
153 * The following is used with VIRTIO_RING_F_EVENT_IDX.
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
160 vring_need_event(uint16_t event_idx, uint16_t new_idx, uint16_t old)
163 return (uint16_t)(new_idx - event_idx - 1) < (uint16_t)(new_idx - old);
165 #endif /* VIRTIO_RING_H */