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  * 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 <stdint.h>
35 #include "standard-headers/linux/types.h"
36 #include "standard-headers/linux/virtio_types.h"
37 
38 /* This marks a buffer as continuing via the next field. */
39 #define VRING_DESC_F_NEXT	1
40 /* This marks a buffer as write-only (otherwise read-only). */
41 #define VRING_DESC_F_WRITE	2
42 /* This means the buffer contains a list of buffer descriptors. */
43 #define VRING_DESC_F_INDIRECT	4
44 
45 /*
46  * Mark a descriptor as available or used in packed ring.
47  * Notice: they are defined as shifts instead of shifted values.
48  */
49 #define VRING_PACKED_DESC_F_AVAIL	7
50 #define VRING_PACKED_DESC_F_USED	15
51 
52 /* The Host uses this in used->flags to advise the Guest: don't kick me when
53  * you add a buffer.  It's unreliable, so it's simply an optimization.  Guest
54  * will still kick if it's out of buffers. */
55 #define VRING_USED_F_NO_NOTIFY	1
56 /* The Guest uses this in avail->flags to advise the Host: don't interrupt me
57  * when you consume a buffer.  It's unreliable, so it's simply an
58  * optimization.  */
59 #define VRING_AVAIL_F_NO_INTERRUPT	1
60 
61 /* Enable events in packed ring. */
62 #define VRING_PACKED_EVENT_FLAG_ENABLE	0x0
63 /* Disable events in packed ring. */
64 #define VRING_PACKED_EVENT_FLAG_DISABLE	0x1
65 /*
66  * Enable events for a specific descriptor in packed ring.
67  * (as specified by Descriptor Ring Change Event Offset/Wrap Counter).
68  * Only valid if VIRTIO_RING_F_EVENT_IDX has been negotiated.
69  */
70 #define VRING_PACKED_EVENT_FLAG_DESC	0x2
71 
72 /*
73  * Wrap counter bit shift in event suppression structure
74  * of packed ring.
75  */
76 #define VRING_PACKED_EVENT_F_WRAP_CTR	15
77 
78 /* We support indirect buffer descriptors */
79 #define VIRTIO_RING_F_INDIRECT_DESC	28
80 
81 /* The Guest publishes the used index for which it expects an interrupt
82  * at the end of the avail ring. Host should ignore the avail->flags field. */
83 /* The Host publishes the avail index for which it expects a kick
84  * at the end of the used ring. Guest should ignore the used->flags field. */
85 #define VIRTIO_RING_F_EVENT_IDX		29
86 
87 /* Alignment requirements for vring elements.
88  * When using pre-virtio 1.0 layout, these fall out naturally.
89  */
90 #define VRING_AVAIL_ALIGN_SIZE 2
91 #define VRING_USED_ALIGN_SIZE 4
92 #define VRING_DESC_ALIGN_SIZE 16
93 
94 /**
95  * struct vring_desc - Virtio ring descriptors,
96  * 16 bytes long. These can chain together via @next.
97  *
98  * @addr: buffer address (guest-physical)
99  * @len: buffer length
100  * @flags: descriptor flags
101  * @next: index of the next descriptor in the chain,
102  *        if the VRING_DESC_F_NEXT flag is set. We chain unused
103  *        descriptors via this, too.
104  */
105 struct vring_desc {
106 	__virtio64 addr;
107 	__virtio32 len;
108 	__virtio16 flags;
109 	__virtio16 next;
110 };
111 
112 struct vring_avail {
113 	__virtio16 flags;
114 	__virtio16 idx;
115 	__virtio16 ring[];
116 };
117 
118 /* uint32_t is used here for ids for padding reasons. */
119 struct vring_used_elem {
120 	/* Index of start of used descriptor chain. */
121 	__virtio32 id;
122 	/* Total length of the descriptor chain which was used (written to) */
123 	__virtio32 len;
124 };
125 
126 typedef struct vring_used_elem __attribute__((aligned(VRING_USED_ALIGN_SIZE)))
127 	vring_used_elem_t;
128 
129 struct vring_used {
130 	__virtio16 flags;
131 	__virtio16 idx;
132 	vring_used_elem_t ring[];
133 };
134 
135 /*
136  * The ring element addresses are passed between components with different
137  * alignments assumptions. Thus, we might need to decrease the compiler-selected
138  * alignment, and so must use a typedef to make sure the aligned attribute
139  * actually takes hold:
140  *
141  * https://gcc.gnu.org/onlinedocs//gcc/Common-Type-Attributes.html#Common-Type-Attributes
142  *
143  * When used on a struct, or struct member, the aligned attribute can only
144  * increase the alignment; in order to decrease it, the packed attribute must
145  * be specified as well. When used as part of a typedef, the aligned attribute
146  * can both increase and decrease alignment, and specifying the packed
147  * attribute generates a warning.
148  */
149 typedef struct vring_desc __attribute__((aligned(VRING_DESC_ALIGN_SIZE)))
150 	vring_desc_t;
151 typedef struct vring_avail __attribute__((aligned(VRING_AVAIL_ALIGN_SIZE)))
152 	vring_avail_t;
153 typedef struct vring_used __attribute__((aligned(VRING_USED_ALIGN_SIZE)))
154 	vring_used_t;
155 
156 struct vring {
157 	unsigned int num;
158 
159 	vring_desc_t *desc;
160 
161 	vring_avail_t *avail;
162 
163 	vring_used_t *used;
164 };
165 
166 #ifndef VIRTIO_RING_NO_LEGACY
167 
168 /* The standard layout for the ring is a continuous chunk of memory which looks
169  * like this.  We assume num is a power of 2.
170  *
171  * struct vring
172  * {
173  *	// The actual descriptors (16 bytes each)
174  *	struct vring_desc desc[num];
175  *
176  *	// A ring of available descriptor heads with free-running index.
177  *	__virtio16 avail_flags;
178  *	__virtio16 avail_idx;
179  *	__virtio16 available[num];
180  *	__virtio16 used_event_idx;
181  *
182  *	// Padding to the next align boundary.
183  *	char pad[];
184  *
185  *	// A ring of used descriptor heads with free-running index.
186  *	__virtio16 used_flags;
187  *	__virtio16 used_idx;
188  *	struct vring_used_elem used[num];
189  *	__virtio16 avail_event_idx;
190  * };
191  */
192 /* We publish the used event index at the end of the available ring, and vice
193  * versa. They are at the end for backwards compatibility. */
194 #define vring_used_event(vr) ((vr)->avail->ring[(vr)->num])
195 #define vring_avail_event(vr) (*(__virtio16 *)&(vr)->used->ring[(vr)->num])
196 
vring_init(struct vring * vr,unsigned int num,void * p,unsigned long align)197 static inline void vring_init(struct vring *vr, unsigned int num, void *p,
198 			      unsigned long align)
199 {
200 	vr->num = num;
201 	vr->desc = p;
202 	vr->avail = (struct vring_avail *)((char *)p + num * sizeof(struct vring_desc));
203 	vr->used = (void *)(((uintptr_t)&vr->avail->ring[num] + sizeof(__virtio16)
204 		+ align-1) & ~(align - 1));
205 }
206 
vring_size(unsigned int num,unsigned long align)207 static inline unsigned vring_size(unsigned int num, unsigned long align)
208 {
209 	return ((sizeof(struct vring_desc) * num + sizeof(__virtio16) * (3 + num)
210 		 + align - 1) & ~(align - 1))
211 		+ sizeof(__virtio16) * 3 + sizeof(struct vring_used_elem) * num;
212 }
213 
214 #endif /* VIRTIO_RING_NO_LEGACY */
215 
216 /* The following is used with USED_EVENT_IDX and AVAIL_EVENT_IDX */
217 /* Assuming a given event_idx value from the other side, if
218  * we have just incremented index from old to new_idx,
219  * should we trigger an event? */
vring_need_event(uint16_t event_idx,uint16_t new_idx,uint16_t old)220 static inline int vring_need_event(uint16_t event_idx, uint16_t new_idx, uint16_t old)
221 {
222 	/* Note: Xen has similar logic for notification hold-off
223 	 * in include/xen/interface/io/ring.h with req_event and req_prod
224 	 * corresponding to event_idx + 1 and new_idx respectively.
225 	 * Note also that req_event and req_prod in Xen start at 1,
226 	 * event indexes in virtio start at 0. */
227 	return (uint16_t)(new_idx - event_idx - 1) < (uint16_t)(new_idx - old);
228 }
229 
230 struct vring_packed_desc_event {
231 	/* Descriptor Ring Change Event Offset/Wrap Counter. */
232 	uint16_t off_wrap;
233 	/* Descriptor Ring Change Event Flags. */
234 	uint16_t flags;
235 };
236 
237 struct vring_packed_desc {
238 	/* Buffer Address. */
239 	uint64_t addr;
240 	/* Buffer Length. */
241 	uint32_t len;
242 	/* Buffer ID. */
243 	uint16_t id;
244 	/* The flags depending on descriptor type. */
245 	uint16_t flags;
246 };
247 
248 #endif /* _LINUX_VIRTIO_RING_H */
249