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1.1 root 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: * 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);
1.1.1.2 ! root 138: vr->used = (void *)(((unsigned long)&vr->avail->ring[num] + sizeof(__u16)
! 139: + align-1) & ~(align - 1));
1.1 root 140: }
141:
142: static __inline__ unsigned vring_size(unsigned int num, unsigned long align)
143: {
1.1.1.2 ! root 144: return ((sizeof(struct vring_desc) * num + sizeof(__u16) * (3 + num)
1.1 root 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 /* _LINUX_VIRTIO_RING_H */
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