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 * 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 * Copyright Rusty Russell IBM Corporation 2007. */
11 #include <linux/types.h>
12
13 /* This marks a buffer as continuing via the next field. */
14 #define VRING_DESC_F_NEXT 1
15 /* This marks a buffer as write-only (otherwise read-only). */
16 #define VRING_DESC_F_WRITE 2
17
18 /* The Host uses this in used->flags to advise the Guest: don't kick me when
19 * you add a buffer. It's unreliable, so it's simply an optimization. Guest
20 * will still kick if it's out of buffers. */
21 #define VRING_USED_F_NO_NOTIFY 1
22 /* The Guest uses this in avail->flags to advise the Host: don't interrupt me
23 * when you consume a buffer. It's unreliable, so it's simply an
24 * optimization. */
25 #define VRING_AVAIL_F_NO_INTERRUPT 1
26
27 /* Virtio ring descriptors: 16 bytes. These can chain together via "next". */
28 struct vring_desc
29 {
30 /* Address (guest-physical). */
31 __u64 addr;
32 /* Length. */
33 __u32 len;
34 /* The flags as indicated above. */
35 __u16 flags;
36 /* We chain unused descriptors via this, too */
37 __u16 next;
38 };
39
40 struct vring_avail
41 {
42 __u16 flags;
43 __u16 idx;
44 __u16 ring[];
45 };
46
47 /* u32 is used here for ids for padding reasons. */
48 struct vring_used_elem
49 {
50 /* Index of start of used descriptor chain. */
51 __u32 id;
52 /* Total length of the descriptor chain which was used (written to) */
53 __u32 len;
54 };
55
56 struct vring_used
57 {
58 __u16 flags;
59 __u16 idx;
60 struct vring_used_elem ring[];
61 };
62
63 struct vring {
64 unsigned int num;
65
66 struct vring_desc *desc;
67
68 struct vring_avail *avail;
69
70 struct vring_used *used;
71 };
72
73 /* The standard layout for the ring is a continuous chunk of memory which looks
74 * like this. We assume num is a power of 2.
75 *
76 * struct vring
77 * {
78 * // The actual descriptors (16 bytes each)
79 * struct vring_desc desc[num];
80 *
81 * // A ring of available descriptor heads with free-running index.
82 * __u16 avail_flags;
83 * __u16 avail_idx;
84 * __u16 available[num];
85 *
86 * // Padding to the next page boundary.
87 * char pad[];
88 *
89 * // A ring of used descriptor heads with free-running index.
90 * __u16 used_flags;
91 * __u16 used_idx;
92 * struct vring_used_elem used[num];
93 * };
94 */
vring_init(struct vring * vr,unsigned int num,void * p,unsigned long pagesize)95 static __inline__ void vring_init(struct vring *vr, unsigned int num, void *p,
96 unsigned long pagesize)
97 {
98 vr->num = num;
99 vr->desc = p;
100 vr->avail = p + num*sizeof(struct vring_desc);
101 vr->used = (void *)(((unsigned long)&vr->avail->ring[num] + pagesize-1)
102 & ~(pagesize - 1));
103 }
104
vring_size(unsigned int num,unsigned long pagesize)105 static __inline__ unsigned vring_size(unsigned int num, unsigned long pagesize)
106 {
107 return ((sizeof(struct vring_desc) * num + sizeof(__u16) * (2 + num)
108 + pagesize - 1) & ~(pagesize - 1))
109 + sizeof(__u16) * 2 + sizeof(struct vring_used_elem) * num;
110 }
111
112 #endif /* _LINUX_VIRTIO_RING_H */
113