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 #include <linux/types.h>
35 #include <linux/virtio_types.h>
36
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
43
44 /*
45 * Mark a descriptor as available or used in packed ring.
46 * Notice: they are defined as shifts instead of shifted values.
47 */
48 #define VRING_PACKED_DESC_F_AVAIL 7
49 #define VRING_PACKED_DESC_F_USED 15
50
51 /* The Host uses this in used->flags to advise the Guest: don't kick me when
52 * you add a buffer. It's unreliable, so it's simply an optimization. Guest
53 * will still kick if it's out of buffers. */
54 #define VRING_USED_F_NO_NOTIFY 1
55 /* The Guest uses this in avail->flags to advise the Host: don't interrupt me
56 * when you consume a buffer. It's unreliable, so it's simply an
57 * optimization. */
58 #define VRING_AVAIL_F_NO_INTERRUPT 1
59
60 /* Enable events in packed ring. */
61 #define VRING_PACKED_EVENT_FLAG_ENABLE 0x0
62 /* Disable events in packed ring. */
63 #define VRING_PACKED_EVENT_FLAG_DISABLE 0x1
64 /*
65 * Enable events for a specific descriptor in packed ring.
66 * (as specified by Descriptor Ring Change Event Offset/Wrap Counter).
67 * Only valid if VIRTIO_RING_F_EVENT_IDX has been negotiated.
68 */
69 #define VRING_PACKED_EVENT_FLAG_DESC 0x2
70
71 /*
72 * Wrap counter bit shift in event suppression structure
73 * of packed ring.
74 */
75 #define VRING_PACKED_EVENT_F_WRAP_CTR 15
76
77 /* We support indirect buffer descriptors */
78 #define VIRTIO_RING_F_INDIRECT_DESC 28
79
80 /* The Guest publishes the used index for which it expects an interrupt
81 * at the end of the avail ring. Host should ignore the avail->flags field. */
82 /* The Host publishes the avail index for which it expects a kick
83 * at the end of the used ring. Guest should ignore the used->flags field. */
84 #define VIRTIO_RING_F_EVENT_IDX 29
85
86 /* Alignment requirements for vring elements.
87 * When using pre-virtio 1.0 layout, these fall out naturally.
88 */
89 #define VRING_AVAIL_ALIGN_SIZE 2
90 #define VRING_USED_ALIGN_SIZE 4
91 #define VRING_DESC_ALIGN_SIZE 16
92
93 /**
94 * struct vring_desc - Virtio ring descriptors,
95 * 16 bytes long. These can chain together via @next.
96 *
97 * @addr: buffer address (guest-physical)
98 * @len: buffer length
99 * @flags: descriptor flags
100 * @next: index of the next descriptor in the chain,
101 * if the VRING_DESC_F_NEXT flag is set. We chain unused
102 * descriptors via this, too.
103 */
104 struct vring_desc {
105 __virtio64 addr;
106 __virtio32 len;
107 __virtio16 flags;
108 __virtio16 next;
109 };
110
111 struct vring_avail {
112 __virtio16 flags;
113 __virtio16 idx;
114 __virtio16 ring[];
115 };
116
117 /* u32 is used here for ids for padding reasons. */
118 struct vring_used_elem {
119 /* Index of start of used descriptor chain. */
120 __virtio32 id;
121 /* Total length of the descriptor chain which was used (written to) */
122 __virtio32 len;
123 };
124
125 typedef struct vring_used_elem __attribute__((aligned(VRING_USED_ALIGN_SIZE)))
126 vring_used_elem_t;
127
128 struct vring_used {
129 __virtio16 flags;
130 __virtio16 idx;
131 vring_used_elem_t ring[];
132 };
133
134 /*
135 * The ring element addresses are passed between components with different
136 * alignments assumptions. Thus, we might need to decrease the compiler-selected
137 * alignment, and so must use a typedef to make sure the aligned attribute
138 * actually takes hold:
139 *
140 * https://gcc.gnu.org/onlinedocs//gcc/Common-Type-Attributes.html#Common-Type-Attributes
141 *
142 * When used on a struct, or struct member, the aligned attribute can only
143 * increase the alignment; in order to decrease it, the packed attribute must
144 * be specified as well. When used as part of a typedef, the aligned attribute
145 * can both increase and decrease alignment, and specifying the packed
146 * attribute generates a warning.
147 */
148 typedef struct vring_desc __attribute__((aligned(VRING_DESC_ALIGN_SIZE)))
149 vring_desc_t;
150 typedef struct vring_avail __attribute__((aligned(VRING_AVAIL_ALIGN_SIZE)))
151 vring_avail_t;
152 typedef struct vring_used __attribute__((aligned(VRING_USED_ALIGN_SIZE)))
153 vring_used_t;
154
155 struct vring {
156 unsigned int num;
157
158 vring_desc_t *desc;
159
160 vring_avail_t *avail;
161
162 vring_used_t *used;
163 };
164
165 #ifndef VIRTIO_RING_NO_LEGACY
166
167 /* The standard layout for the ring is a continuous chunk of memory which looks
168 * like this. We assume num is a power of 2.
169 *
170 * struct vring
171 * {
172 * // The actual descriptors (16 bytes each)
173 * struct vring_desc desc[num];
174 *
175 * // A ring of available descriptor heads with free-running index.
176 * __virtio16 avail_flags;
177 * __virtio16 avail_idx;
178 * __virtio16 available[num];
179 * __virtio16 used_event_idx;
180 *
181 * // Padding to the next align boundary.
182 * char pad[];
183 *
184 * // A ring of used descriptor heads with free-running index.
185 * __virtio16 used_flags;
186 * __virtio16 used_idx;
187 * struct vring_used_elem used[num];
188 * __virtio16 avail_event_idx;
189 * };
190 */
191 /* We publish the used event index at the end of the available ring, and vice
192 * versa. They are at the end for backwards compatibility. */
193 #define vring_used_event(vr) ((vr)->avail->ring[(vr)->num])
194 #define vring_avail_event(vr) (*(__virtio16 *)&(vr)->used->ring[(vr)->num])
195
vring_init(struct vring * vr,unsigned int num,void * p,unsigned long align)196 static inline void vring_init(struct vring *vr, unsigned int num, void *p,
197 unsigned long align)
198 {
199 vr->num = num;
200 vr->desc = p;
201 vr->avail = (struct vring_avail *)((char *)p + num * sizeof(struct vring_desc));
202 vr->used = (void *)(((unsigned long)&vr->avail->ring[num] + sizeof(__virtio16)
203 + align-1) & ~(align - 1));
204 }
205
vring_size(unsigned int num,unsigned long align)206 static inline unsigned vring_size(unsigned int num, unsigned long align)
207 {
208 return ((sizeof(struct vring_desc) * num + sizeof(__virtio16) * (3 + num)
209 + align - 1) & ~(align - 1))
210 + sizeof(__virtio16) * 3 + sizeof(struct vring_used_elem) * num;
211 }
212
213 #endif /* VIRTIO_RING_NO_LEGACY */
214
215 /* The following is used with USED_EVENT_IDX and AVAIL_EVENT_IDX */
216 /* Assuming a given event_idx value from the other side, if
217 * we have just incremented index from old to new_idx,
218 * should we trigger an event? */
vring_need_event(__u16 event_idx,__u16 new_idx,__u16 old)219 static inline int vring_need_event(__u16 event_idx, __u16 new_idx, __u16 old)
220 {
221 /* Note: Xen has similar logic for notification hold-off
222 * in include/xen/interface/io/ring.h with req_event and req_prod
223 * corresponding to event_idx + 1 and new_idx respectively.
224 * Note also that req_event and req_prod in Xen start at 1,
225 * event indexes in virtio start at 0. */
226 return (__u16)(new_idx - event_idx - 1) < (__u16)(new_idx - old);
227 }
228
229 struct vring_packed_desc_event {
230 /* Descriptor Ring Change Event Offset/Wrap Counter. */
231 __le16 off_wrap;
232 /* Descriptor Ring Change Event Flags. */
233 __le16 flags;
234 };
235
236 struct vring_packed_desc {
237 /* Buffer Address. */
238 __le64 addr;
239 /* Buffer Length. */
240 __le32 len;
241 /* Buffer ID. */
242 __le16 id;
243 /* The flags depending on descriptor type. */
244 __le16 flags;
245 };
246
247 #endif /* _UAPI_LINUX_VIRTIO_RING_H */
248