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#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/* The Host uses this in used->flags to advise the Guest: don't kick me when
45 * you add a buffer.  It's unreliable, so it's simply an optimization.  Guest
46 * will still kick if it's out of buffers. */
47#define VRING_USED_F_NO_NOTIFY	1
48/* The Guest uses this in avail->flags to advise the Host: don't interrupt me
49 * when you consume a buffer.  It's unreliable, so it's simply an
50 * optimization.  */
51#define VRING_AVAIL_F_NO_INTERRUPT	1
52
53/* We support indirect buffer descriptors */
54#define VIRTIO_RING_F_INDIRECT_DESC	28
55
56/* The Guest publishes the used index for which it expects an interrupt
57 * at the end of the avail ring. Host should ignore the avail->flags field. */
58/* The Host publishes the avail index for which it expects a kick
59 * at the end of the used ring. Guest should ignore the used->flags field. */
60#define VIRTIO_RING_F_EVENT_IDX		29
61
62/* Virtio ring descriptors: 16 bytes.  These can chain together via "next". */
63struct vring_desc {
64	/* Address (guest-physical). */
65	__virtio64 addr;
66	/* Length. */
67	__virtio32 len;
68	/* The flags as indicated above. */
69	__virtio16 flags;
70	/* We chain unused descriptors via this, too */
71	__virtio16 next;
72};
73
74struct vring_avail {
75	__virtio16 flags;
76	__virtio16 idx;
77	__virtio16 ring[];
78};
79
80/* u32 is used here for ids for padding reasons. */
81struct vring_used_elem {
82	/* Index of start of used descriptor chain. */
83	__virtio32 id;
84	/* Total length of the descriptor chain which was used (written to) */
85	__virtio32 len;
86};
87
88struct vring_used {
89	__virtio16 flags;
90	__virtio16 idx;
91	struct vring_used_elem ring[];
92};
93
94struct vring {
95	unsigned int num;
96
97	struct vring_desc *desc;
98
99	struct vring_avail *avail;
100
101	struct vring_used *used;
102};
103
104/* Alignment requirements for vring elements.
105 * When using pre-virtio 1.0 layout, these fall out naturally.
106 */
107#define VRING_AVAIL_ALIGN_SIZE 2
108#define VRING_USED_ALIGN_SIZE 4
109#define VRING_DESC_ALIGN_SIZE 16
110
111/* The standard layout for the ring is a continuous chunk of memory which looks
112 * like this.  We assume num is a power of 2.
113 *
114 * struct vring
115 * {
116 *	// The actual descriptors (16 bytes each)
117 *	struct vring_desc desc[num];
118 *
119 *	// A ring of available descriptor heads with free-running index.
120 *	__virtio16 avail_flags;
121 *	__virtio16 avail_idx;
122 *	__virtio16 available[num];
123 *	__virtio16 used_event_idx;
124 *
125 *	// Padding to the next align boundary.
126 *	char pad[];
127 *
128 *	// A ring of used descriptor heads with free-running index.
129 *	__virtio16 used_flags;
130 *	__virtio16 used_idx;
131 *	struct vring_used_elem used[num];
132 *	__virtio16 avail_event_idx;
133 * };
134 */
135/* We publish the used event index at the end of the available ring, and vice
136 * versa. They are at the end for backwards compatibility. */
137#define vring_used_event(vr) ((vr)->avail->ring[(vr)->num])
138#define vring_avail_event(vr) (*(__virtio16 *)&(vr)->used->ring[(vr)->num])
139
140static inline void vring_init(struct vring *vr, unsigned int num, void *p,
141			      unsigned long align)
142{
143	vr->num = num;
144	vr->desc = p;
145	vr->avail = p + num*sizeof(struct vring_desc);
146	vr->used = (void *)(((unsigned long)&vr->avail->ring[num] + sizeof(__virtio16)
147		+ align-1) & ~(align - 1));
148}
149
150static inline unsigned vring_size(unsigned int num, unsigned long align)
151{
152	return ((sizeof(struct vring_desc) * num + sizeof(__virtio16) * (3 + num)
153		 + align - 1) & ~(align - 1))
154		+ sizeof(__virtio16) * 3 + sizeof(struct vring_used_elem) * num;
155}
156
157/* The following is used with USED_EVENT_IDX and AVAIL_EVENT_IDX */
158/* Assuming a given event_idx value from the other side, if
159 * we have just incremented index from old to new_idx,
160 * should we trigger an event? */
161static inline int vring_need_event(__u16 event_idx, __u16 new_idx, __u16 old)
162{
163	/* Note: Xen has similar logic for notification hold-off
164	 * in include/xen/interface/io/ring.h with req_event and req_prod
165	 * corresponding to event_idx + 1 and new_idx respectively.
166	 * Note also that req_event and req_prod in Xen start at 1,
167	 * event indexes in virtio start at 0. */
168	return (__u16)(new_idx - event_idx - 1) < (__u16)(new_idx - old);
169}
170
171#endif /* _UAPI_LINUX_VIRTIO_RING_H */
172