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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 | * and lguest, 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 | ||
36 | /* This marks a buffer as continuing via the next field. */ | |
37 | #define VRING_DESC_F_NEXT 1 | |
38 | /* This marks a buffer as write-only (otherwise read-only). */ | |
39 | #define VRING_DESC_F_WRITE 2 | |
40 | /* This means the buffer contains a list of buffer descriptors. */ | |
41 | #define VRING_DESC_F_INDIRECT 4 | |
42 | ||
43 | /* The Host uses this in used->flags to advise the Guest: don't kick me when | |
44 | * you add a buffer. It's unreliable, so it's simply an optimization. Guest | |
45 | * will still kick if it's out of buffers. */ | |
46 | #define VRING_USED_F_NO_NOTIFY 1 | |
47 | /* The Guest uses this in avail->flags to advise the Host: don't interrupt me | |
48 | * when you consume a buffer. It's unreliable, so it's simply an | |
49 | * optimization. */ | |
50 | #define VRING_AVAIL_F_NO_INTERRUPT 1 | |
51 | ||
52 | /* We support indirect buffer descriptors */ | |
53 | #define VIRTIO_RING_F_INDIRECT_DESC 28 | |
54 | ||
55 | /* The Guest publishes the used index for which it expects an interrupt | |
56 | * at the end of the avail ring. Host should ignore the avail->flags field. */ | |
57 | /* The Host publishes the avail index for which it expects a kick | |
58 | * at the end of the used ring. Guest should ignore the used->flags field. */ | |
59 | #define VIRTIO_RING_F_EVENT_IDX 29 | |
60 | ||
61 | /* Virtio ring descriptors: 16 bytes. These can chain together via "next". */ | |
62 | struct vring_desc { | |
63 | /* Address (guest-physical). */ | |
64 | __u64 addr; | |
65 | /* Length. */ | |
66 | __u32 len; | |
67 | /* The flags as indicated above. */ | |
68 | __u16 flags; | |
69 | /* We chain unused descriptors via this, too */ | |
70 | __u16 next; | |
71 | }; | |
72 | ||
73 | struct vring_avail { | |
74 | __u16 flags; | |
75 | __u16 idx; | |
76 | __u16 ring[]; | |
77 | }; | |
78 | ||
79 | /* u32 is used here for ids for padding reasons. */ | |
80 | struct vring_used_elem { | |
81 | /* Index of start of used descriptor chain. */ | |
82 | __u32 id; | |
83 | /* Total length of the descriptor chain which was used (written to) */ | |
84 | __u32 len; | |
85 | }; | |
86 | ||
87 | struct vring_used { | |
88 | __u16 flags; | |
89 | __u16 idx; | |
90 | struct vring_used_elem ring[]; | |
91 | }; | |
92 | ||
93 | struct vring { | |
94 | unsigned int num; | |
95 | ||
96 | struct vring_desc *desc; | |
97 | ||
98 | struct vring_avail *avail; | |
99 | ||
100 | struct vring_used *used; | |
101 | }; | |
102 | ||
103 | /* The standard layout for the ring is a continuous chunk of memory which looks | |
104 | * like this. We assume num is a power of 2. | |
105 | * | |
106 | * struct vring | |
107 | * { | |
108 | * // The actual descriptors (16 bytes each) | |
109 | * struct vring_desc desc[num]; | |
110 | * | |
111 | * // A ring of available descriptor heads with free-running index. | |
112 | * __u16 avail_flags; | |
113 | * __u16 avail_idx; | |
114 | * __u16 available[num]; | |
115 | * __u16 used_event_idx; | |
116 | * | |
117 | * // Padding to the next align boundary. | |
118 | * char pad[]; | |
119 | * | |
120 | * // A ring of used descriptor heads with free-running index. | |
121 | * __u16 used_flags; | |
122 | * __u16 used_idx; | |
123 | * struct vring_used_elem used[num]; | |
124 | * __u16 avail_event_idx; | |
125 | * }; | |
126 | */ | |
127 | /* We publish the used event index at the end of the available ring, and vice | |
128 | * versa. They are at the end for backwards compatibility. */ | |
129 | #define vring_used_event(vr) ((vr)->avail->ring[(vr)->num]) | |
130 | #define vring_avail_event(vr) (*(__u16 *)&(vr)->used->ring[(vr)->num]) | |
131 | ||
132 | static inline void vring_init(struct vring *vr, unsigned int num, void *p, | |
133 | unsigned long align) | |
134 | { | |
135 | vr->num = num; | |
136 | vr->desc = p; | |
137 | vr->avail = p + num*sizeof(struct vring_desc); | |
138 | vr->used = (void *)(((unsigned long)&vr->avail->ring[num] + sizeof(__u16) | |
139 | + align-1) & ~(align - 1)); | |
140 | } | |
141 | ||
142 | static inline unsigned vring_size(unsigned int num, unsigned long align) | |
143 | { | |
144 | return ((sizeof(struct vring_desc) * num + sizeof(__u16) * (3 + num) | |
145 | + align - 1) & ~(align - 1)) | |
146 | + sizeof(__u16) * 3 + sizeof(struct vring_used_elem) * num; | |
147 | } | |
148 | ||
149 | /* The following is used with USED_EVENT_IDX and AVAIL_EVENT_IDX */ | |
150 | /* Assuming a given event_idx value from the other size, if | |
151 | * we have just incremented index from old to new_idx, | |
152 | * should we trigger an event? */ | |
153 | static inline int vring_need_event(__u16 event_idx, __u16 new_idx, __u16 old) | |
154 | { | |
155 | /* Note: Xen has similar logic for notification hold-off | |
156 | * in include/xen/interface/io/ring.h with req_event and req_prod | |
157 | * corresponding to event_idx + 1 and new_idx respectively. | |
158 | * Note also that req_event and req_prod in Xen start at 1, | |
159 | * event indexes in virtio start at 0. */ | |
160 | return (__u16)(new_idx - event_idx - 1) < (__u16)(new_idx - old); | |
161 | } | |
162 | ||
163 | #endif /* _UAPI_LINUX_VIRTIO_RING_H */ |