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 /* Virtio ring descriptors: 16 bytes. These can chain together via "next". */ 88 struct vring_desc { 89 /* Address (guest-physical). */ 90 __virtio64 addr; 91 /* Length. */ 92 __virtio32 len; 93 /* The flags as indicated above. */ 94 __virtio16 flags; 95 /* We chain unused descriptors via this, too */ 96 __virtio16 next; 97 }; 98 99 struct vring_avail { 100 __virtio16 flags; 101 __virtio16 idx; 102 __virtio16 ring[]; 103 }; 104 105 /* uint32_t is used here for ids for padding reasons. */ 106 struct vring_used_elem { 107 /* Index of start of used descriptor chain. */ 108 __virtio32 id; 109 /* Total length of the descriptor chain which was used (written to) */ 110 __virtio32 len; 111 }; 112 113 struct vring_used { 114 __virtio16 flags; 115 __virtio16 idx; 116 struct vring_used_elem ring[]; 117 }; 118 119 struct vring { 120 unsigned int num; 121 122 struct vring_desc *desc; 123 124 struct vring_avail *avail; 125 126 struct vring_used *used; 127 }; 128 129 /* Alignment requirements for vring elements. 130 * When using pre-virtio 1.0 layout, these fall out naturally. 131 */ 132 #define VRING_AVAIL_ALIGN_SIZE 2 133 #define VRING_USED_ALIGN_SIZE 4 134 #define VRING_DESC_ALIGN_SIZE 16 135 136 /* The standard layout for the ring is a continuous chunk of memory which looks 137 * like this. We assume num is a power of 2. 138 * 139 * struct vring 140 * { 141 * // The actual descriptors (16 bytes each) 142 * struct vring_desc desc[num]; 143 * 144 * // A ring of available descriptor heads with free-running index. 145 * __virtio16 avail_flags; 146 * __virtio16 avail_idx; 147 * __virtio16 available[num]; 148 * __virtio16 used_event_idx; 149 * 150 * // Padding to the next align boundary. 151 * char pad[]; 152 * 153 * // A ring of used descriptor heads with free-running index. 154 * __virtio16 used_flags; 155 * __virtio16 used_idx; 156 * struct vring_used_elem used[num]; 157 * __virtio16 avail_event_idx; 158 * }; 159 */ 160 /* We publish the used event index at the end of the available ring, and vice 161 * versa. They are at the end for backwards compatibility. */ 162 #define vring_used_event(vr) ((vr)->avail->ring[(vr)->num]) 163 #define vring_avail_event(vr) (*(__virtio16 *)&(vr)->used->ring[(vr)->num]) 164 165 static inline void vring_init(struct vring *vr, unsigned int num, void *p, 166 unsigned long align) 167 { 168 vr->num = num; 169 vr->desc = p; 170 vr->avail = p + num*sizeof(struct vring_desc); 171 vr->used = (void *)(((uintptr_t)&vr->avail->ring[num] + sizeof(__virtio16) 172 + align-1) & ~(align - 1)); 173 } 174 175 static inline unsigned vring_size(unsigned int num, unsigned long align) 176 { 177 return ((sizeof(struct vring_desc) * num + sizeof(__virtio16) * (3 + num) 178 + align - 1) & ~(align - 1)) 179 + sizeof(__virtio16) * 3 + sizeof(struct vring_used_elem) * num; 180 } 181 182 /* The following is used with USED_EVENT_IDX and AVAIL_EVENT_IDX */ 183 /* Assuming a given event_idx value from the other side, if 184 * we have just incremented index from old to new_idx, 185 * should we trigger an event? */ 186 static inline int vring_need_event(uint16_t event_idx, uint16_t new_idx, uint16_t old) 187 { 188 /* Note: Xen has similar logic for notification hold-off 189 * in include/xen/interface/io/ring.h with req_event and req_prod 190 * corresponding to event_idx + 1 and new_idx respectively. 191 * Note also that req_event and req_prod in Xen start at 1, 192 * event indexes in virtio start at 0. */ 193 return (uint16_t)(new_idx - event_idx - 1) < (uint16_t)(new_idx - old); 194 } 195 196 struct vring_packed_desc_event { 197 /* Descriptor Ring Change Event Offset/Wrap Counter. */ 198 uint16_t off_wrap; 199 /* Descriptor Ring Change Event Flags. */ 200 uint16_t flags; 201 }; 202 203 struct vring_packed_desc { 204 /* Buffer Address. */ 205 uint64_t addr; 206 /* Buffer Length. */ 207 uint32_t len; 208 /* Buffer ID. */ 209 uint16_t id; 210 /* The flags depending on descriptor type. */ 211 uint16_t flags; 212 }; 213 214 struct vring_packed { 215 unsigned int num; 216 217 struct vring_packed_desc *desc; 218 219 struct vring_packed_desc_event *driver; 220 221 struct vring_packed_desc_event *device; 222 }; 223 224 #endif /* _LINUX_VIRTIO_RING_H */ 225