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1 | #ifndef _LINUX_VIRTIO_RING_H |
2 | #define _LINUX_VIRTIO_RING_H | |
d4083f50 AP |
3 | /* An interface for efficient virtio implementation, currently for use by KVM, |
4 | * but hopefully others soon. Do NOT change this since it will | |
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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. */ | |
120758fb | 34 | #include <stdint.h> |
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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 | /* The Host uses this in used->flags to advise the Guest: don't kick me when | |
46 | * you add a buffer. It's unreliable, so it's simply an optimization. Guest | |
47 | * will still kick if it's out of buffers. */ | |
48 | #define VRING_USED_F_NO_NOTIFY 1 | |
49 | /* The Guest uses this in avail->flags to advise the Host: don't interrupt me | |
50 | * when you consume a buffer. It's unreliable, so it's simply an | |
51 | * optimization. */ | |
52 | #define VRING_AVAIL_F_NO_INTERRUPT 1 | |
53 | ||
54 | /* We support indirect buffer descriptors */ | |
55 | #define VIRTIO_RING_F_INDIRECT_DESC 28 | |
56 | ||
57 | /* The Guest publishes the used index for which it expects an interrupt | |
58 | * at the end of the avail ring. Host should ignore the avail->flags field. */ | |
59 | /* The Host publishes the avail index for which it expects a kick | |
60 | * at the end of the used ring. Guest should ignore the used->flags field. */ | |
61 | #define VIRTIO_RING_F_EVENT_IDX 29 | |
62 | ||
63 | /* Virtio ring descriptors: 16 bytes. These can chain together via "next". */ | |
64 | struct vring_desc { | |
65 | /* Address (guest-physical). */ | |
66 | __virtio64 addr; | |
67 | /* Length. */ | |
68 | __virtio32 len; | |
69 | /* The flags as indicated above. */ | |
70 | __virtio16 flags; | |
71 | /* We chain unused descriptors via this, too */ | |
72 | __virtio16 next; | |
73 | }; | |
74 | ||
75 | struct vring_avail { | |
76 | __virtio16 flags; | |
77 | __virtio16 idx; | |
78 | __virtio16 ring[]; | |
79 | }; | |
80 | ||
81 | /* u32 is used here for ids for padding reasons. */ | |
82 | struct vring_used_elem { | |
83 | /* Index of start of used descriptor chain. */ | |
84 | __virtio32 id; | |
85 | /* Total length of the descriptor chain which was used (written to) */ | |
86 | __virtio32 len; | |
87 | }; | |
88 | ||
89 | struct vring_used { | |
90 | __virtio16 flags; | |
91 | __virtio16 idx; | |
92 | struct vring_used_elem ring[]; | |
93 | }; | |
94 | ||
95 | struct vring { | |
96 | unsigned int num; | |
97 | ||
98 | struct vring_desc *desc; | |
99 | ||
100 | struct vring_avail *avail; | |
101 | ||
102 | struct vring_used *used; | |
103 | }; | |
104 | ||
105 | /* Alignment requirements for vring elements. | |
106 | * When using pre-virtio 1.0 layout, these fall out naturally. | |
107 | */ | |
108 | #define VRING_AVAIL_ALIGN_SIZE 2 | |
109 | #define VRING_USED_ALIGN_SIZE 4 | |
110 | #define VRING_DESC_ALIGN_SIZE 16 | |
111 | ||
112 | /* The standard layout for the ring is a continuous chunk of memory which looks | |
113 | * like this. We assume num is a power of 2. | |
114 | * | |
115 | * struct vring | |
116 | * { | |
117 | * // The actual descriptors (16 bytes each) | |
118 | * struct vring_desc desc[num]; | |
119 | * | |
120 | * // A ring of available descriptor heads with free-running index. | |
121 | * __virtio16 avail_flags; | |
122 | * __virtio16 avail_idx; | |
123 | * __virtio16 available[num]; | |
124 | * __virtio16 used_event_idx; | |
125 | * | |
126 | * // Padding to the next align boundary. | |
127 | * char pad[]; | |
128 | * | |
129 | * // A ring of used descriptor heads with free-running index. | |
130 | * __virtio16 used_flags; | |
131 | * __virtio16 used_idx; | |
132 | * struct vring_used_elem used[num]; | |
133 | * __virtio16 avail_event_idx; | |
134 | * }; | |
135 | */ | |
136 | /* We publish the used event index at the end of the available ring, and vice | |
137 | * versa. They are at the end for backwards compatibility. */ | |
138 | #define vring_used_event(vr) ((vr)->avail->ring[(vr)->num]) | |
139 | #define vring_avail_event(vr) (*(__virtio16 *)&(vr)->used->ring[(vr)->num]) | |
140 | ||
e0d2be2a | 141 | static inline void vring_init(struct vring *vr, unsigned int num, void *p, |
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142 | unsigned long align) |
143 | { | |
144 | vr->num = num; | |
145 | vr->desc = p; | |
146 | vr->avail = p + num*sizeof(struct vring_desc); | |
120758fb | 147 | vr->used = (void *)(((uintptr_t)&vr->avail->ring[num] + sizeof(__virtio16) |
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148 | + align-1) & ~(align - 1)); |
149 | } | |
150 | ||
e0d2be2a | 151 | static inline unsigned vring_size(unsigned int num, unsigned long align) |
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152 | { |
153 | return ((sizeof(struct vring_desc) * num + sizeof(__virtio16) * (3 + num) | |
154 | + align - 1) & ~(align - 1)) | |
155 | + sizeof(__virtio16) * 3 + sizeof(struct vring_used_elem) * num; | |
156 | } | |
157 | ||
158 | /* The following is used with USED_EVENT_IDX and AVAIL_EVENT_IDX */ | |
24a31426 | 159 | /* Assuming a given event_idx value from the other side, if |
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160 | * we have just incremented index from old to new_idx, |
161 | * should we trigger an event? */ | |
e0d2be2a | 162 | static inline int vring_need_event(uint16_t event_idx, uint16_t new_idx, uint16_t old) |
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163 | { |
164 | /* Note: Xen has similar logic for notification hold-off | |
165 | * in include/xen/interface/io/ring.h with req_event and req_prod | |
166 | * corresponding to event_idx + 1 and new_idx respectively. | |
167 | * Note also that req_event and req_prod in Xen start at 1, | |
168 | * event indexes in virtio start at 0. */ | |
169 | return (uint16_t)(new_idx - event_idx - 1) < (uint16_t)(new_idx - old); | |
170 | } | |
171 | ||
172 | #endif /* _LINUX_VIRTIO_RING_H */ |