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'' 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 #include <stdint.h>
35 #include "standard-headers/linux/types.h"
36 #include "standard-headers/linux/virtio_types.h"
37
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
44
45 /*
46 * Mark a descriptor as available or used in packed ring.
47 * Notice: they are defined as shifts instead of shifted values.
48 */
49 #define VRING_PACKED_DESC_F_AVAIL 7
50 #define VRING_PACKED_DESC_F_USED 15
51
52 /* The Host uses this in used->flags to advise the Guest: don't kick me when
53 * you add a buffer. It's unreliable, so it's simply an optimization. Guest
54 * will still kick if it's out of buffers. */
55 #define VRING_USED_F_NO_NOTIFY 1
56 /* The Guest uses this in avail->flags to advise the Host: don't interrupt me
57 * when you consume a buffer. It's unreliable, so it's simply an
58 * optimization. */
59 #define VRING_AVAIL_F_NO_INTERRUPT 1
60
61 /* Enable events in packed ring. */
62 #define VRING_PACKED_EVENT_FLAG_ENABLE 0x0
63 /* Disable events in packed ring. */
64 #define VRING_PACKED_EVENT_FLAG_DISABLE 0x1
65 /*
66 * Enable events for a specific descriptor in packed ring.
67 * (as specified by Descriptor Ring Change Event Offset/Wrap Counter).
68 * Only valid if VIRTIO_RING_F_EVENT_IDX has been negotiated.
69 */
70 #define VRING_PACKED_EVENT_FLAG_DESC 0x2
71
72 /*
73 * Wrap counter bit shift in event suppression structure
74 * of packed ring.
75 */
76 #define VRING_PACKED_EVENT_F_WRAP_CTR 15
77
78 /* We support indirect buffer descriptors */
79 #define VIRTIO_RING_F_INDIRECT_DESC 28
80
81 /* The Guest publishes the used index for which it expects an interrupt
82 * at the end of the avail ring. Host should ignore the avail->flags field. */
83 /* The Host publishes the avail index for which it expects a kick
84 * at the end of the used ring. Guest should ignore the used->flags field. */
85 #define VIRTIO_RING_F_EVENT_IDX 29
86
87 /* Alignment requirements for vring elements.
88 * When using pre-virtio 1.0 layout, these fall out naturally.
89 */
90 #define VRING_AVAIL_ALIGN_SIZE 2
91 #define VRING_USED_ALIGN_SIZE 4
92 #define VRING_DESC_ALIGN_SIZE 16
93
94 /**
95 * struct vring_desc - Virtio ring descriptors,
96 * 16 bytes long. These can chain together via @next.
97 *
98 * @addr: buffer address (guest-physical)
99 * @len: buffer length
100 * @flags: descriptor flags
101 * @next: index of the next descriptor in the chain,
102 * if the VRING_DESC_F_NEXT flag is set. We chain unused
103 * descriptors via this, too.
104 */
105 struct vring_desc {
106 __virtio64 addr;
107 __virtio32 len;
108 __virtio16 flags;
109 __virtio16 next;
110 };
111
112 struct vring_avail {
113 __virtio16 flags;
114 __virtio16 idx;
115 __virtio16 ring[];
116 };
117
118 /* uint32_t is used here for ids for padding reasons. */
119 struct vring_used_elem {
120 /* Index of start of used descriptor chain. */
121 __virtio32 id;
122 /* Total length of the descriptor chain which was used (written to) */
123 __virtio32 len;
124 };
125
126 typedef struct vring_used_elem __attribute__((aligned(VRING_USED_ALIGN_SIZE)))
127 vring_used_elem_t;
128
129 struct vring_used {
130 __virtio16 flags;
131 __virtio16 idx;
132 vring_used_elem_t ring[];
133 };
134
135 /*
136 * The ring element addresses are passed between components with different
137 * alignments assumptions. Thus, we might need to decrease the compiler-selected
138 * alignment, and so must use a typedef to make sure the aligned attribute
139 * actually takes hold:
140 *
141 * https://gcc.gnu.org/onlinedocs//gcc/Common-Type-Attributes.html#Common-Type-Attributes
142 *
143 * When used on a struct, or struct member, the aligned attribute can only
144 * increase the alignment; in order to decrease it, the packed attribute must
145 * be specified as well. When used as part of a typedef, the aligned attribute
146 * can both increase and decrease alignment, and specifying the packed
147 * attribute generates a warning.
148 */
149 typedef struct vring_desc __attribute__((aligned(VRING_DESC_ALIGN_SIZE)))
150 vring_desc_t;
151 typedef struct vring_avail __attribute__((aligned(VRING_AVAIL_ALIGN_SIZE)))
152 vring_avail_t;
153 typedef struct vring_used __attribute__((aligned(VRING_USED_ALIGN_SIZE)))
154 vring_used_t;
155
156 struct vring {
157 unsigned int num;
158
159 vring_desc_t *desc;
160
161 vring_avail_t *avail;
162
163 vring_used_t *used;
164 };
165
166 #ifndef VIRTIO_RING_NO_LEGACY
167
168 /* The standard layout for the ring is a continuous chunk of memory which looks
169 * like this. We assume num is a power of 2.
170 *
171 * struct vring
172 * {
173 * // The actual descriptors (16 bytes each)
174 * struct vring_desc desc[num];
175 *
176 * // A ring of available descriptor heads with free-running index.
177 * __virtio16 avail_flags;
178 * __virtio16 avail_idx;
179 * __virtio16 available[num];
180 * __virtio16 used_event_idx;
181 *
182 * // Padding to the next align boundary.
183 * char pad[];
184 *
185 * // A ring of used descriptor heads with free-running index.
186 * __virtio16 used_flags;
187 * __virtio16 used_idx;
188 * struct vring_used_elem used[num];
189 * __virtio16 avail_event_idx;
190 * };
191 */
192 /* We publish the used event index at the end of the available ring, and vice
193 * versa. They are at the end for backwards compatibility. */
194 #define vring_used_event(vr) ((vr)->avail->ring[(vr)->num])
195 #define vring_avail_event(vr) (*(__virtio16 *)&(vr)->used->ring[(vr)->num])
196
vring_init(struct vring * vr,unsigned int num,void * p,unsigned long align)197 static inline void vring_init(struct vring *vr, unsigned int num, void *p,
198 unsigned long align)
199 {
200 vr->num = num;
201 vr->desc = p;
202 vr->avail = (struct vring_avail *)((char *)p + num * sizeof(struct vring_desc));
203 vr->used = (void *)(((uintptr_t)&vr->avail->ring[num] + sizeof(__virtio16)
204 + align-1) & ~(align - 1));
205 }
206
vring_size(unsigned int num,unsigned long align)207 static inline unsigned vring_size(unsigned int num, unsigned long align)
208 {
209 return ((sizeof(struct vring_desc) * num + sizeof(__virtio16) * (3 + num)
210 + align - 1) & ~(align - 1))
211 + sizeof(__virtio16) * 3 + sizeof(struct vring_used_elem) * num;
212 }
213
214 #endif /* VIRTIO_RING_NO_LEGACY */
215
216 /* The following is used with USED_EVENT_IDX and AVAIL_EVENT_IDX */
217 /* Assuming a given event_idx value from the other side, if
218 * we have just incremented index from old to new_idx,
219 * should we trigger an event? */
vring_need_event(uint16_t event_idx,uint16_t new_idx,uint16_t old)220 static inline int vring_need_event(uint16_t event_idx, uint16_t new_idx, uint16_t old)
221 {
222 /* Note: Xen has similar logic for notification hold-off
223 * in include/xen/interface/io/ring.h with req_event and req_prod
224 * corresponding to event_idx + 1 and new_idx respectively.
225 * Note also that req_event and req_prod in Xen start at 1,
226 * event indexes in virtio start at 0. */
227 return (uint16_t)(new_idx - event_idx - 1) < (uint16_t)(new_idx - old);
228 }
229
230 struct vring_packed_desc_event {
231 /* Descriptor Ring Change Event Offset/Wrap Counter. */
232 uint16_t off_wrap;
233 /* Descriptor Ring Change Event Flags. */
234 uint16_t flags;
235 };
236
237 struct vring_packed_desc {
238 /* Buffer Address. */
239 uint64_t addr;
240 /* Buffer Length. */
241 uint32_t len;
242 /* Buffer ID. */
243 uint16_t id;
244 /* The flags depending on descriptor type. */
245 uint16_t flags;
246 };
247
248 #endif /* _LINUX_VIRTIO_RING_H */
249