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  * 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 #ifndef __KERNEL__
35 #include <stdint.h>
36 #endif
37 #include <linux/types.h>
38 #include <linux/virtio_types.h>
39 
40 /* This marks a buffer as continuing via the next field. */
41 #define VRING_DESC_F_NEXT	1
42 /* This marks a buffer as write-only (otherwise read-only). */
43 #define VRING_DESC_F_WRITE	2
44 /* This means the buffer contains a list of buffer descriptors. */
45 #define VRING_DESC_F_INDIRECT	4
46 
47 /*
48  * Mark a descriptor as available or used in packed ring.
49  * Notice: they are defined as shifts instead of shifted values.
50  */
51 #define VRING_PACKED_DESC_F_AVAIL	7
52 #define VRING_PACKED_DESC_F_USED	15
53 
54 /* The Host uses this in used->flags to advise the Guest: don't kick me when
55  * you add a buffer.  It's unreliable, so it's simply an optimization.  Guest
56  * will still kick if it's out of buffers. */
57 #define VRING_USED_F_NO_NOTIFY	1
58 /* The Guest uses this in avail->flags to advise the Host: don't interrupt me
59  * when you consume a buffer.  It's unreliable, so it's simply an
60  * optimization.  */
61 #define VRING_AVAIL_F_NO_INTERRUPT	1
62 
63 /* Enable events in packed ring. */
64 #define VRING_PACKED_EVENT_FLAG_ENABLE	0x0
65 /* Disable events in packed ring. */
66 #define VRING_PACKED_EVENT_FLAG_DISABLE	0x1
67 /*
68  * Enable events for a specific descriptor in packed ring.
69  * (as specified by Descriptor Ring Change Event Offset/Wrap Counter).
70  * Only valid if VIRTIO_RING_F_EVENT_IDX has been negotiated.
71  */
72 #define VRING_PACKED_EVENT_FLAG_DESC	0x2
73 
74 /*
75  * Wrap counter bit shift in event suppression structure
76  * of packed ring.
77  */
78 #define VRING_PACKED_EVENT_F_WRAP_CTR	15
79 
80 /* We support indirect buffer descriptors */
81 #define VIRTIO_RING_F_INDIRECT_DESC	28
82 
83 /* The Guest publishes the used index for which it expects an interrupt
84  * at the end of the avail ring. Host should ignore the avail->flags field. */
85 /* The Host publishes the avail index for which it expects a kick
86  * at the end of the used ring. Guest should ignore the used->flags field. */
87 #define VIRTIO_RING_F_EVENT_IDX		29
88 
89 /* Alignment requirements for vring elements.
90  * When using pre-virtio 1.0 layout, these fall out naturally.
91  */
92 #define VRING_AVAIL_ALIGN_SIZE 2
93 #define VRING_USED_ALIGN_SIZE 4
94 #define VRING_DESC_ALIGN_SIZE 16
95 
96 /* Virtio ring descriptors: 16 bytes.  These can chain together via "next". */
97 struct vring_desc {
98 	/* Address (guest-physical). */
99 	__virtio64 addr;
100 	/* Length. */
101 	__virtio32 len;
102 	/* The flags as indicated above. */
103 	__virtio16 flags;
104 	/* We chain unused descriptors via this, too */
105 	__virtio16 next;
106 };
107 
108 struct vring_avail {
109 	__virtio16 flags;
110 	__virtio16 idx;
111 	__virtio16 ring[];
112 };
113 
114 /* u32 is used here for ids for padding reasons. */
115 struct vring_used_elem {
116 	/* Index of start of used descriptor chain. */
117 	__virtio32 id;
118 	/* Total length of the descriptor chain which was used (written to) */
119 	__virtio32 len;
120 };
121 
122 typedef struct vring_used_elem __attribute__((aligned(VRING_USED_ALIGN_SIZE)))
123 	vring_used_elem_t;
124 
125 struct vring_used {
126 	__virtio16 flags;
127 	__virtio16 idx;
128 	vring_used_elem_t ring[];
129 };
130 
131 /*
132  * The ring element addresses are passed between components with different
133  * alignments assumptions. Thus, we might need to decrease the compiler-selected
134  * alignment, and so must use a typedef to make sure the aligned attribute
135  * actually takes hold:
136  *
137  * https://gcc.gnu.org/onlinedocs//gcc/Common-Type-Attributes.html#Common-Type-Attributes
138  *
139  * When used on a struct, or struct member, the aligned attribute can only
140  * increase the alignment; in order to decrease it, the packed attribute must
141  * be specified as well. When used as part of a typedef, the aligned attribute
142  * can both increase and decrease alignment, and specifying the packed
143  * attribute generates a warning.
144  */
145 typedef struct vring_desc __attribute__((aligned(VRING_DESC_ALIGN_SIZE)))
146 	vring_desc_t;
147 typedef struct vring_avail __attribute__((aligned(VRING_AVAIL_ALIGN_SIZE)))
148 	vring_avail_t;
149 typedef struct vring_used __attribute__((aligned(VRING_USED_ALIGN_SIZE)))
150 	vring_used_t;
151 
152 struct vring {
153 	unsigned int num;
154 
155 	vring_desc_t *desc;
156 
157 	vring_avail_t *avail;
158 
159 	vring_used_t *used;
160 };
161 
162 #ifndef VIRTIO_RING_NO_LEGACY
163 
164 /* The standard layout for the ring is a continuous chunk of memory which looks
165  * like this.  We assume num is a power of 2.
166  *
167  * struct vring
168  * {
169  *	// The actual descriptors (16 bytes each)
170  *	struct vring_desc desc[num];
171  *
172  *	// A ring of available descriptor heads with free-running index.
173  *	__virtio16 avail_flags;
174  *	__virtio16 avail_idx;
175  *	__virtio16 available[num];
176  *	__virtio16 used_event_idx;
177  *
178  *	// Padding to the next align boundary.
179  *	char pad[];
180  *
181  *	// A ring of used descriptor heads with free-running index.
182  *	__virtio16 used_flags;
183  *	__virtio16 used_idx;
184  *	struct vring_used_elem used[num];
185  *	__virtio16 avail_event_idx;
186  * };
187  */
188 /* We publish the used event index at the end of the available ring, and vice
189  * versa. They are at the end for backwards compatibility. */
190 #define vring_used_event(vr) ((vr)->avail->ring[(vr)->num])
191 #define vring_avail_event(vr) (*(__virtio16 *)&(vr)->used->ring[(vr)->num])
192 
vring_init(struct vring * vr,unsigned int num,void * p,unsigned long align)193 static inline void vring_init(struct vring *vr, unsigned int num, void *p,
194 			      unsigned long align)
195 {
196 	vr->num = num;
197 	vr->desc = p;
198 	vr->avail = (struct vring_avail *)((char *)p + num * sizeof(struct vring_desc));
199 	vr->used = (void *)(((uintptr_t)&vr->avail->ring[num] + sizeof(__virtio16)
200 		+ align-1) & ~(align - 1));
201 }
202 
vring_size(unsigned int num,unsigned long align)203 static inline unsigned vring_size(unsigned int num, unsigned long align)
204 {
205 	return ((sizeof(struct vring_desc) * num + sizeof(__virtio16) * (3 + num)
206 		 + align - 1) & ~(align - 1))
207 		+ sizeof(__virtio16) * 3 + sizeof(struct vring_used_elem) * num;
208 }
209 
210 #endif /* VIRTIO_RING_NO_LEGACY */
211 
212 /* The following is used with USED_EVENT_IDX and AVAIL_EVENT_IDX */
213 /* Assuming a given event_idx value from the other side, if
214  * we have just incremented index from old to new_idx,
215  * should we trigger an event? */
vring_need_event(__u16 event_idx,__u16 new_idx,__u16 old)216 static inline int vring_need_event(__u16 event_idx, __u16 new_idx, __u16 old)
217 {
218 	/* Note: Xen has similar logic for notification hold-off
219 	 * in include/xen/interface/io/ring.h with req_event and req_prod
220 	 * corresponding to event_idx + 1 and new_idx respectively.
221 	 * Note also that req_event and req_prod in Xen start at 1,
222 	 * event indexes in virtio start at 0. */
223 	return (__u16)(new_idx - event_idx - 1) < (__u16)(new_idx - old);
224 }
225 
226 struct vring_packed_desc_event {
227 	/* Descriptor Ring Change Event Offset/Wrap Counter. */
228 	__le16 off_wrap;
229 	/* Descriptor Ring Change Event Flags. */
230 	__le16 flags;
231 };
232 
233 struct vring_packed_desc {
234 	/* Buffer Address. */
235 	__le64 addr;
236 	/* Buffer Length. */
237 	__le32 len;
238 	/* Buffer ID. */
239 	__le16 id;
240 	/* The flags depending on descriptor type. */
241 	__le16 flags;
242 };
243 
244 #endif /* _UAPI_LINUX_VIRTIO_RING_H */
245