1 /*
2 * Copyright Rusty Russell IBM Corporation 2007.
3 *
4 * SPDX-License-Identifier: BSD-3-Clause
5 *
6 * $FreeBSD$
7 */
8
9 #ifndef VIRTIO_RING_H
10 #define VIRTIO_RING_H
11
12 #include <metal/compiler.h>
13
14 #if defined __cplusplus
15 extern "C" {
16 #endif
17
18 /* This marks a buffer as continuing via the next field. */
19 #define VRING_DESC_F_NEXT 1
20 /* This marks a buffer as write-only (otherwise read-only). */
21 #define VRING_DESC_F_WRITE 2
22 /* This means the buffer contains a list of buffer descriptors. */
23 #define VRING_DESC_F_INDIRECT 4
24
25 /* The Host uses this in used->flags to advise the Guest: don't kick me
26 * when you add a buffer. It's unreliable, so it's simply an
27 * optimization. Guest will still kick if it's out of buffers.
28 */
29 #define VRING_USED_F_NO_NOTIFY 1
30 /* The Guest uses this in avail->flags to advise the Host: don't
31 * interrupt me when you consume a buffer. It's unreliable, so it's
32 * simply an optimization.
33 */
34 #define VRING_AVAIL_F_NO_INTERRUPT 1
35
36 /**
37 * @brief VirtIO ring descriptors.
38 *
39 * The descriptor table refers to the buffers the driver is using for the
40 * device. addr is a physical address, and the buffers can be chained via \ref next.
41 * Each descriptor describes a buffer which is read-only for the device
42 * (“device-readable”) or write-only for the device (“device-writable”), but a
43 * chain of descriptors can contain both device-readable and device-writable
44 * buffers.
45 */
46 METAL_PACKED_BEGIN
47 struct vring_desc {
48 /** Address (guest-physical) */
49 uint64_t addr;
50
51 /** Length */
52 uint32_t len;
53
54 /** Flags relevant to the descriptors */
55 uint16_t flags;
56
57 /** We chain unused descriptors via this, too */
58 uint16_t next;
59 } METAL_PACKED_END;
60
61 /**
62 * @brief Used to offer buffers to the device.
63 *
64 * Each ring entry refers to the head of a descriptor chain. It is only
65 * written by the driver and read by the device.
66 */
67 METAL_PACKED_BEGIN
68 struct vring_avail {
69 /** Flag which determines whether device notifications are required */
70 uint16_t flags;
71
72 /**
73 * Indicates where the driver puts the next descriptor entry in the
74 * ring (modulo the queue size)
75 */
76 uint16_t idx;
77
78 /** The ring of descriptors */
79 uint16_t ring[0];
80 } METAL_PACKED_END;
81
82 /* uint32_t is used here for ids for padding reasons. */
83 METAL_PACKED_BEGIN
84 struct vring_used_elem {
85 union {
86 uint16_t event;
87 /* Index of start of used descriptor chain. */
88 uint32_t id;
89 };
90 /* Total length of the descriptor chain which was written to. */
91 uint32_t len;
92 } METAL_PACKED_END;
93
94 /**
95 * @brief The device returns buffers to this structure when done with them
96 *
97 * The structure is only written to by the device, and read by the driver.
98 */
99 METAL_PACKED_BEGIN
100 struct vring_used {
101 /** Flag which determines whether device notifications are required */
102 uint16_t flags;
103
104 /**
105 * Indicates where the driver puts the next descriptor entry in the
106 * ring (modulo the queue size)
107 */
108 uint16_t idx;
109
110 /** The ring of descriptors */
111 struct vring_used_elem ring[0];
112 } METAL_PACKED_END;
113
114 /**
115 * @brief The virtqueue layout structure
116 *
117 * Each virtqueue consists of; descriptor table, available ring, used ring,
118 * where each part is physically contiguous in guest memory.
119 *
120 * When the driver wants to send a buffer to the device, it fills in a slot in
121 * the descriptor table (or chains several together), and writes the descriptor
122 * index into the available ring. It then notifies the device. When the device
123 * has finished a buffer, it writes the descriptor index into the used ring,
124 * and sends an interrupt.
125 *
126 * The standard layout for the ring is a continuous chunk of memory which
127 * looks like this. We assume num is a power of 2.
128 *
129 * struct vring {
130 * // The actual descriptors (16 bytes each)
131 * struct vring_desc desc[num];
132 *
133 * // A ring of available descriptor heads with free-running index.
134 * __u16 avail_flags;
135 * __u16 avail_idx;
136 * __u16 available[num];
137 * __u16 used_event_idx;
138 *
139 * // Padding to the next align boundary.
140 * char pad[];
141 *
142 * // A ring of used descriptor heads with free-running index.
143 * __u16 used_flags;
144 * __u16 used_idx;
145 * struct vring_used_elem used[num];
146 * __u16 avail_event_idx;
147 * };
148 *
149 * NOTE: for VirtIO PCI, align is 4096.
150 */
151 struct vring {
152 /**
153 * The maximum number of buffer descriptors in the virtqueue.
154 * The value is always a power of 2.
155 */
156 unsigned int num;
157
158 /** The actual buffer descriptors, 16 bytes each */
159 struct vring_desc *desc;
160
161 /** A ring of available descriptor heads with free-running index */
162 struct vring_avail *avail;
163
164 /** A ring of used descriptor heads with free-running index */
165 struct vring_used *used;
166 };
167
168 /*
169 * We publish the used event index at the end of the available ring, and vice
170 * versa. They are at the end for backwards compatibility.
171 */
172 #define vring_used_event(vr) ((vr)->avail->ring[(vr)->num])
173 #define vring_avail_event(vr) ((vr)->used->ring[(vr)->num].event)
174
vring_size(unsigned int num,unsigned long align)175 static inline int vring_size(unsigned int num, unsigned long align)
176 {
177 int size;
178
179 size = num * sizeof(struct vring_desc);
180 size += sizeof(struct vring_avail) + (num * sizeof(uint16_t)) +
181 sizeof(uint16_t);
182 size = (size + align - 1) & ~(align - 1);
183 size += sizeof(struct vring_used) +
184 (num * sizeof(struct vring_used_elem)) + sizeof(uint16_t);
185
186 return size;
187 }
188
189 static inline void
vring_init(struct vring * vr,unsigned int num,uint8_t * p,unsigned long align)190 vring_init(struct vring *vr, unsigned int num, uint8_t *p, unsigned long align)
191 {
192 vr->num = num;
193 vr->desc = (struct vring_desc *)p;
194 vr->avail = (struct vring_avail *)(p + num * sizeof(struct vring_desc));
195 vr->used = (struct vring_used *)
196 (((unsigned long)&vr->avail->ring[num] + sizeof(uint16_t) +
197 align - 1) & ~(align - 1));
198 }
199
200 /*
201 * The following is used with VIRTIO_RING_F_EVENT_IDX.
202 *
203 * Assuming a given event_idx value from the other size, if we have
204 * just incremented index from old to new_idx, should we trigger an
205 * event?
206 */
207 static inline int
vring_need_event(uint16_t event_idx,uint16_t new_idx,uint16_t old)208 vring_need_event(uint16_t event_idx, uint16_t new_idx, uint16_t old)
209 {
210 return (uint16_t)(new_idx - event_idx - 1) <
211 (uint16_t)(new_idx - old);
212 }
213
214 #if defined __cplusplus
215 }
216 #endif
217
218 #endif /* VIRTIO_RING_H */
219
