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 * 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
22 '' AND
23 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
24 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
25 * ARE DISCLAIMED. IN NO EVENT SHALL IBM OR CONTRIBUTORS BE LIABLE
26 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
27 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
28 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
29 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
30 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
31 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
32 * SUCH DAMAGE.
33 *
34 * Copyright Rusty Russell IBM Corporation 2007. */
35 #ifndef __KERNEL__
36 #include <stdint.h>
37 #endif
38 #include <linux/types.h>
39 #include <linux/virtio_types.h>
40
41 /* This marks a buffer as continuing via the next field. */
42 #define VRING_DESC_F_NEXT 1
43 /* This marks a buffer as write-only (otherwise read-only). */
44 #define VRING_DESC_F_WRITE 2
45 /* This means the buffer contains a list of buffer descriptors. */
46 #define VRING_DESC_F_INDIRECT 4
47
48 /*
49 * Mark a descriptor as available or used in packed ring.
50 * Notice: they are defined as shifts instead of shifted values.
51 */
52 #define VRING_PACKED_DESC_F_AVAIL 7
53 #define VRING_PACKED_DESC_F_USED 15
54
55 /* The Host uses this in used->flags to advise the Guest: don't kick me when
56 * you add a buffer. It's unreliable, so it's simply an optimization. Guest
57 * will still kick if it's out of buffers. */
58 #define VRING_USED_F_NO_NOTIFY 1
59 /* The Guest uses this in avail->flags to advise the Host: don't interrupt me
60 * when you consume a buffer. It's unreliable, so it's simply an
61 * optimization. */
62 #define VRING_AVAIL_F_NO_INTERRUPT 1
63
64 /* Enable events in packed ring. */
65 #define VRING_PACKED_EVENT_FLAG_ENABLE 0x0
66 /* Disable events in packed ring. */
67 #define VRING_PACKED_EVENT_FLAG_DISABLE 0x1
68 /*
69 * Enable events for a specific descriptor in packed ring.
70 * (as specified by Descriptor Ring Change Event Offset/Wrap Counter).
71 * Only valid if VIRTIO_RING_F_EVENT_IDX has been negotiated.
72 */
73 #define VRING_PACKED_EVENT_FLAG_DESC 0x2
74
75 /*
76 * Wrap counter bit shift in event suppression structure
77 * of packed ring.
78 */
79 #define VRING_PACKED_EVENT_F_WRAP_CTR 15
80
81 /* We support indirect buffer descriptors */
82 #define VIRTIO_RING_F_INDIRECT_DESC 28
83
84 /* The Guest publishes the used index for which it expects an interrupt
85 * at the end of the avail ring. Host should ignore the avail->flags field. */
86 /* The Host publishes the avail index for which it expects a kick
87 * at the end of the used ring. Guest should ignore the used->flags field. */
88 #define VIRTIO_RING_F_EVENT_IDX 29
89
90 /* Virtio ring descriptors: 16 bytes. These can chain together via "next". */
91 struct vring_desc {
92 /* Address (guest-physical). */
93 __virtio64 addr;
94 /* Length. */
95 __virtio32 len;
96 /* The flags as indicated above. */
97 __virtio16 flags;
98 /* We chain unused descriptors via this, too */
99 __virtio16 next;
100 };
101
102 struct vring_avail {
103 __virtio16 flags;
104 __virtio16 idx;
105 __virtio16 ring[];
106 };
107
108 /* u32 is used here for ids for padding reasons. */
109 struct vring_used_elem {
110 /* Index of start of used descriptor chain. */
111 __virtio32 id;
112 /* Total length of the descriptor chain which was used (written to) */
113 __virtio32 len;
114 };
115
116 struct vring_used {
117 __virtio16 flags;
118 __virtio16 idx;
119 struct vring_used_elem ring[];
120 };
121
122 struct vring {
123 unsigned int num;
124
125 struct vring_desc *desc;
126
127 struct vring_avail *avail;
128
129 struct vring_used *used;
130 };
131
132 /* Alignment requirements for vring elements.
133 * When using pre-virtio 1.0 layout, these fall out naturally.
134 */
135 #define VRING_AVAIL_ALIGN_SIZE 2
136 #define VRING_USED_ALIGN_SIZE 4
137 #define VRING_DESC_ALIGN_SIZE 16
138
139 /* The standard layout for the ring is a continuous chunk of memory which looks
140 * like this. We assume num is a power of 2.
141 *
142 * struct vring
143 * {
144 * The actual descriptors (16 bytes each)
145 * struct vring_desc desc[num];
146 *
147 * A ring of available descriptor heads with free-running index.
148 * __virtio16 avail_flags;
149 * __virtio16 avail_idx;
150 * __virtio16 available[num];
151 * __virtio16 used_event_idx;
152 *
153 * Padding to the next align boundary.
154 * char pad[];
155 *
156 * A ring of used descriptor heads with free-running index.
157 * __virtio16 used_flags;
158 * __virtio16 used_idx;
159 * struct vring_used_elem used[num];
160 * __virtio16 avail_event_idx;
161 * };
162 */
163 /* We publish the used event index at the end of the available ring, and vice
164 * versa. They are at the end for backwards compatibility. */
165 #define vring_used_event(vr) ((vr)->avail->ring[(vr)->num])
166 #define vring_avail_event(vr) (*(__virtio16 *)&(vr)->used->ring[(vr)->num])
167
168 static inline void
vring_init(struct vring * vr,unsigned int num,void * p,unsigned long align)169 vring_init(struct vring *vr, unsigned int num, void *p,
170 unsigned long align)
171 {
172 vr->num = num;
173 vr->desc = p;
174 vr->avail = (struct vring_avail *)((char *)p + num * sizeof(struct vring_desc
175 ));
176 vr->used = (void *)(((uintptr_t)&vr->avail->ring[num] + sizeof(__virtio16)
177 + align - 1) & ~(align - 1));
178 }
179
180 static inline unsigned
vring_size(unsigned int num,unsigned long align)181 vring_size(unsigned int num, unsigned long align)
182 {
183 return ((sizeof(struct vring_desc) * num + sizeof(__virtio16) * (3 + num)
184 + align - 1) & ~(align - 1))
185 + sizeof(__virtio16) * 3 + sizeof(struct vring_used_elem) * num;
186 }
187
188 /* The following is used with USED_EVENT_IDX and AVAIL_EVENT_IDX */
189 /* Assuming a given event_idx value from the other side, if
190 * we have just incremented index from old to new_idx,
191 * should we trigger an event? */
192 static inline int
vring_need_event(__u16 event_idx,__u16 new_idx,__u16 old)193 vring_need_event(__u16 event_idx, __u16 new_idx, __u16 old)
194 {
195 /* Note: Xen has similar logic for notification hold-off
196 * in include/xen/interface/io/ring.h with req_event and req_prod
197 * corresponding to event_idx + 1 and new_idx respectively.
198 * Note also that req_event and req_prod in Xen start at 1,
199 * event indexes in virtio start at 0. */
200 return (__u16)(new_idx - event_idx - 1) < (__u16)(new_idx - old);
201 }
202
203 struct vring_packed_desc_event {
204 /* Descriptor Ring Change Event Offset/Wrap Counter. */
205 __le16 off_wrap;
206 /* Descriptor Ring Change Event Flags. */
207 __le16 flags;
208 };
209
210 struct vring_packed_desc {
211 /* Buffer Address. */
212 __le64 addr;
213 /* Buffer Length. */
214 __le32 len;
215 /* Buffer ID. */
216 __le16 id;
217 /* The flags depending on descriptor type. */
218 __le16 flags;
219 };
220
221 #endif /* _LINUX_VIRTIO_RING_H */
222