1 #ifndef _UAPI_LINUX_VIRTIO_RING_H
2 #define _UAPI_LINUX_VIRTIO_RING_H
3 /* An interface for efficient virtio implementation, currently for use by KVM,
4 * but hopefully others soon. Do NOT change this since it will
5 * break existing servers and clients.
6 *
7 * This header is BSD licensed so anyone can use the definitions to implement
8 * compatible drivers/servers.
9 *
10 * Redistribution and use in source and binary forms, with or without
11 * modification, are permitted provided that the following conditions
12 * are met:
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
31 * SUCH DAMAGE.
32 *
33 * Copyright Rusty Russell IBM Corporation 2007. */
34 #ifndef __KERNEL__
35 #include <stdint.h>
36 #endif
37 #include <linux/types.h>
38 #include <linux/virtio_types.h>
39
40 /* This marks a buffer as continuing via the next field. */
41 #define VRING_DESC_F_NEXT 1
42 /* This marks a buffer as write-only (otherwise read-only). */
43 #define VRING_DESC_F_WRITE 2
44 /* This means the buffer contains a list of buffer descriptors. */
45 #define VRING_DESC_F_INDIRECT 4
46
47 /* The Host uses this in used->flags to advise the Guest: don't kick me when
48 * you add a buffer. It's unreliable, so it's simply an optimization. Guest
49 * will still kick if it's out of buffers. */
50 #define VRING_USED_F_NO_NOTIFY 1
51 /* The Guest uses this in avail->flags to advise the Host: don't interrupt me
52 * when you consume a buffer. It's unreliable, so it's simply an
53 * optimization. */
54 #define VRING_AVAIL_F_NO_INTERRUPT 1
55
56 /* We support indirect buffer descriptors */
57 #define VIRTIO_RING_F_INDIRECT_DESC 28
58
59 /* The Guest publishes the used index for which it expects an interrupt
60 * at the end of the avail ring. Host should ignore the avail->flags field. */
61 /* The Host publishes the avail index for which it expects a kick
62 * at the end of the used ring. Guest should ignore the used->flags field. */
63 #define VIRTIO_RING_F_EVENT_IDX 29
64
65 /* Virtio ring descriptors: 16 bytes. These can chain together via "next". */
66 struct vring_desc {
67 /* Address (guest-physical). */
68 __virtio64 addr;
69 /* Length. */
70 __virtio32 len;
71 /* The flags as indicated above. */
72 __virtio16 flags;
73 /* We chain unused descriptors via this, too */
74 __virtio16 next;
75 };
76
77 struct vring_avail {
78 __virtio16 flags;
79 __virtio16 idx;
80 __virtio16 ring[];
81 };
82
83 /* u32 is used here for ids for padding reasons. */
84 struct vring_used_elem {
85 /* Index of start of used descriptor chain. */
86 __virtio32 id;
87 /* Total length of the descriptor chain which was used (written to) */
88 __virtio32 len;
89 };
90
91 struct vring_used {
92 __virtio16 flags;
93 __virtio16 idx;
94 struct vring_used_elem ring[];
95 };
96
97 struct vring {
98 unsigned int num;
99
100 struct vring_desc *desc;
101
102 struct vring_avail *avail;
103
104 struct vring_used *used;
105 };
106
107 /* Alignment requirements for vring elements.
108 * When using pre-virtio 1.0 layout, these fall out naturally.
109 */
110 #define VRING_AVAIL_ALIGN_SIZE 2
111 #define VRING_USED_ALIGN_SIZE 4
112 #define VRING_DESC_ALIGN_SIZE 16
113
114 /* The standard layout for the ring is a continuous chunk of memory which looks
115 * like this. We assume num is a power of 2.
116 *
117 * struct vring
118 * {
119 * // The actual descriptors (16 bytes each)
120 * struct vring_desc desc[num];
121 *
122 * // A ring of available descriptor heads with free-running index.
123 * __virtio16 avail_flags;
124 * __virtio16 avail_idx;
125 * __virtio16 available[num];
126 * __virtio16 used_event_idx;
127 *
128 * // Padding to the next align boundary.
129 * char pad[];
130 *
131 * // A ring of used descriptor heads with free-running index.
132 * __virtio16 used_flags;
133 * __virtio16 used_idx;
134 * struct vring_used_elem used[num];
135 * __virtio16 avail_event_idx;
136 * };
137 */
138 /* We publish the used event index at the end of the available ring, and vice
139 * versa. They are at the end for backwards compatibility. */
140 #define vring_used_event(vr) ((vr)->avail->ring[(vr)->num])
141 #define vring_avail_event(vr) (*(__virtio16 *)&(vr)->used->ring[(vr)->num])
142
vring_init(struct vring * vr,unsigned int num,void * p,unsigned long align)143 static inline void vring_init(struct vring *vr, unsigned int num, void *p,
144 unsigned long align)
145 {
146 vr->num = num;
147 vr->desc = p;
148 vr->avail = p + num*sizeof(struct vring_desc);
149 vr->used = (void *)(((uintptr_t)&vr->avail->ring[num] + sizeof(__virtio16)
150 + align-1) & ~(align - 1));
151 }
152
vring_size(unsigned int num,unsigned long align)153 static inline unsigned vring_size(unsigned int num, unsigned long align)
154 {
155 return ((sizeof(struct vring_desc) * num + sizeof(__virtio16) * (3 + num)
156 + align - 1) & ~(align - 1))
157 + sizeof(__virtio16) * 3 + sizeof(struct vring_used_elem) * num;
158 }
159
160 /* The following is used with USED_EVENT_IDX and AVAIL_EVENT_IDX */
161 /* Assuming a given event_idx value from the other side, if
162 * we have just incremented index from old to new_idx,
163 * should we trigger an event? */
vring_need_event(__u16 event_idx,__u16 new_idx,__u16 old)164 static inline int vring_need_event(__u16 event_idx, __u16 new_idx, __u16 old)
165 {
166 /* Note: Xen has similar logic for notification hold-off
167 * in include/xen/interface/io/ring.h with req_event and req_prod
168 * corresponding to event_idx + 1 and new_idx respectively.
169 * Note also that req_event and req_prod in Xen start at 1,
170 * event indexes in virtio start at 0. */
171 return (__u16)(new_idx - event_idx - 1) < (__u16)(new_idx - old);
172 }
173
174 #endif /* _UAPI_LINUX_VIRTIO_RING_H */
175