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.
7 * This header is BSD licensed so anyone can use the definitions to implement
8 * compatible drivers/servers.
10 * Redistribution and use in source and binary forms, with or without
11 * modification, are permitted provided that the following conditions
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
33 * Copyright Rusty Russell IBM Corporation 2007. */
37 #include <linux/types.h>
38 #include <linux/virtio_types.h>
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
48 * Mark a descriptor as available or used in packed ring.
49 * Notice: they are defined as shifts instead of shifted values.
51 #define VRING_PACKED_DESC_F_AVAIL 7
52 #define VRING_PACKED_DESC_F_USED 15
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
61 #define VRING_AVAIL_F_NO_INTERRUPT 1
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
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.
72 #define VRING_PACKED_EVENT_FLAG_DESC 0x2
75 * Wrap counter bit shift in event suppression structure
78 #define VRING_PACKED_EVENT_F_WRAP_CTR 15
80 /* We support indirect buffer descriptors */
81 #define VIRTIO_RING_F_INDIRECT_DESC 28
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
89 /* Alignment requirements for vring elements.
90 * When using pre-virtio 1.0 layout, these fall out naturally.
92 #define VRING_AVAIL_ALIGN_SIZE 2
93 #define VRING_USED_ALIGN_SIZE 4
94 #define VRING_DESC_ALIGN_SIZE 16
96 /* Virtio ring descriptors: 16 bytes. These can chain together via "next". */
98 /* Address (guest-physical). */
102 /* The flags as indicated above. */
104 /* We chain unused descriptors via this, too */
114 /* u32 is used here for ids for padding reasons. */
115 struct vring_used_elem {
116 /* Index of start of used descriptor chain. */
118 /* Total length of the descriptor chain which was used (written to) */
122 typedef struct vring_used_elem __attribute__((aligned(VRING_USED_ALIGN_SIZE)))
128 vring_used_elem_t ring[];
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:
137 * https://gcc.gnu.org/onlinedocs//gcc/Common-Type-Attributes.html#Common-Type-Attributes
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.
145 typedef struct vring_desc __attribute__((aligned(VRING_DESC_ALIGN_SIZE)))
147 typedef struct vring_avail __attribute__((aligned(VRING_AVAIL_ALIGN_SIZE)))
149 typedef struct vring_used __attribute__((aligned(VRING_USED_ALIGN_SIZE)))
157 vring_avail_t *avail;
162 #ifndef VIRTIO_RING_NO_LEGACY
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.
169 * // The actual descriptors (16 bytes each)
170 * struct vring_desc desc[num];
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;
178 * // Padding to the next align boundary.
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;
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])
193 static inline void vring_init(struct vring *vr, unsigned int num, void *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));
203 static inline unsigned vring_size(unsigned int num, unsigned long align)
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;
210 #endif /* VIRTIO_RING_NO_LEGACY */
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? */
216 static inline int vring_need_event(__u16 event_idx, __u16 new_idx, __u16 old)
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);
226 struct vring_packed_desc_event {
227 /* Descriptor Ring Change Event Offset/Wrap Counter. */
229 /* Descriptor Ring Change Event Flags. */
233 struct vring_packed_desc {
234 /* Buffer Address. */
240 /* The flags depending on descriptor type. */
244 #endif /* _UAPI_LINUX_VIRTIO_RING_H */