1 #ifndef _LINUX_VIRTIO_RING_H
2 #define _LINUX_VIRTIO_RING_H
3 /* An interface for efficient virtio implementation, currently for use by KVM
4 * and lguest, but hopefully others soon. Do NOT change this since it will
5 * break existing servers and clients.
7 * This header is BSD licensed so anyone can use the definitions to implement
8 * compatible drivers/servers.
10 * Redistribution and use in source and binary forms, with or without
11 * modification, are permitted provided that the following conditions
13 * 1. Redistributions of source code must retain the above copyright
14 * notice, this list of conditions and the following disclaimer.
15 * 2. Redistributions in binary form must reproduce the above copyright
16 * notice, this list of conditions and the following disclaimer in the
17 * documentation and/or other materials provided with the distribution.
18 * 3. Neither the name of IBM nor the names of its contributors
19 * may be used to endorse or promote products derived from this software
20 * without specific prior written permission.
21 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS ``AS IS'' AND
22 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
23 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
24 * ARE DISCLAIMED. IN NO EVENT SHALL IBM OR CONTRIBUTORS BE LIABLE
25 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
26 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
27 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
28 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
29 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
30 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
33 * Copyright Rusty Russell IBM Corporation 2007. */
34 #include "standard-headers/linux/types.h"
35 #include "standard-headers/linux/virtio_types.h"
37 /* This marks a buffer as continuing via the next field. */
38 #define VRING_DESC_F_NEXT 1
39 /* This marks a buffer as write-only (otherwise read-only). */
40 #define VRING_DESC_F_WRITE 2
41 /* This means the buffer contains a list of buffer descriptors. */
42 #define VRING_DESC_F_INDIRECT 4
44 /* The Host uses this in used->flags to advise the Guest: don't kick me when
45 * you add a buffer. It's unreliable, so it's simply an optimization. Guest
46 * will still kick if it's out of buffers. */
47 #define VRING_USED_F_NO_NOTIFY 1
48 /* The Guest uses this in avail->flags to advise the Host: don't interrupt me
49 * when you consume a buffer. It's unreliable, so it's simply an
51 #define VRING_AVAIL_F_NO_INTERRUPT 1
53 /* We support indirect buffer descriptors */
54 #define VIRTIO_RING_F_INDIRECT_DESC 28
56 /* The Guest publishes the used index for which it expects an interrupt
57 * at the end of the avail ring. Host should ignore the avail->flags field. */
58 /* The Host publishes the avail index for which it expects a kick
59 * at the end of the used ring. Guest should ignore the used->flags field. */
60 #define VIRTIO_RING_F_EVENT_IDX 29
62 /* Virtio ring descriptors: 16 bytes. These can chain together via "next". */
64 /* Address (guest-physical). */
68 /* The flags as indicated above. */
70 /* We chain unused descriptors via this, too */
80 /* u32 is used here for ids for padding reasons. */
81 struct vring_used_elem
{
82 /* Index of start of used descriptor chain. */
84 /* Total length of the descriptor chain which was used (written to) */
91 struct vring_used_elem ring
[];
97 struct vring_desc
*desc
;
99 struct vring_avail
*avail
;
101 struct vring_used
*used
;
104 /* Alignment requirements for vring elements.
105 * When using pre-virtio 1.0 layout, these fall out naturally.
107 #define VRING_AVAIL_ALIGN_SIZE 2
108 #define VRING_USED_ALIGN_SIZE 4
109 #define VRING_DESC_ALIGN_SIZE 16
111 /* The standard layout for the ring is a continuous chunk of memory which looks
112 * like this. We assume num is a power of 2.
116 * // The actual descriptors (16 bytes each)
117 * struct vring_desc desc[num];
119 * // A ring of available descriptor heads with free-running index.
120 * __virtio16 avail_flags;
121 * __virtio16 avail_idx;
122 * __virtio16 available[num];
123 * __virtio16 used_event_idx;
125 * // Padding to the next align boundary.
128 * // A ring of used descriptor heads with free-running index.
129 * __virtio16 used_flags;
130 * __virtio16 used_idx;
131 * struct vring_used_elem used[num];
132 * __virtio16 avail_event_idx;
135 /* We publish the used event index at the end of the available ring, and vice
136 * versa. They are at the end for backwards compatibility. */
137 #define vring_used_event(vr) ((vr)->avail->ring[(vr)->num])
138 #define vring_avail_event(vr) (*(__virtio16 *)&(vr)->used->ring[(vr)->num])
140 static inline void vring_init(struct vring
*vr
, unsigned int num
, void *p
,
145 vr
->avail
= p
+ num
*sizeof(struct vring_desc
);
146 vr
->used
= (void *)(((unsigned long)&vr
->avail
->ring
[num
] + sizeof(__virtio16
)
147 + align
-1) & ~(align
- 1));
150 static inline unsigned vring_size(unsigned int num
, unsigned long align
)
152 return ((sizeof(struct vring_desc
) * num
+ sizeof(__virtio16
) * (3 + num
)
153 + align
- 1) & ~(align
- 1))
154 + sizeof(__virtio16
) * 3 + sizeof(struct vring_used_elem
) * num
;
157 /* The following is used with USED_EVENT_IDX and AVAIL_EVENT_IDX */
158 /* Assuming a given event_idx value from the other size, if
159 * we have just incremented index from old to new_idx,
160 * should we trigger an event? */
161 static inline int vring_need_event(uint16_t event_idx
, uint16_t new_idx
, uint16_t old
)
163 /* Note: Xen has similar logic for notification hold-off
164 * in include/xen/interface/io/ring.h with req_event and req_prod
165 * corresponding to event_idx + 1 and new_idx respectively.
166 * Note also that req_event and req_prod in Xen start at 1,
167 * event indexes in virtio start at 0. */
168 return (uint16_t)(new_idx
- event_idx
- 1) < (uint16_t)(new_idx
- old
);
171 #endif /* _LINUX_VIRTIO_RING_H */