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 /* Virtio ring descriptors: 16 bytes. These can chain together via "next". */ 95 struct vring_desc { 96 /* Address (guest-physical). */ 97 __virtio64 addr; 98 /* Length. */ 99 __virtio32 len; 100 /* The flags as indicated above. */ 101 __virtio16 flags; 102 /* We chain unused descriptors via this, too */ 103 __virtio16 next; 104 }; 105 106 struct vring_avail { 107 __virtio16 flags; 108 __virtio16 idx; 109 __virtio16 ring[]; 110 }; 111 112 /* uint32_t is used here for ids for padding reasons. */ 113 struct vring_used_elem { 114 /* Index of start of used descriptor chain. */ 115 __virtio32 id; 116 /* Total length of the descriptor chain which was used (written to) */ 117 __virtio32 len; 118 }; 119 120 typedef struct vring_used_elem __attribute__((aligned(VRING_USED_ALIGN_SIZE))) 121 vring_used_elem_t; 122 123 struct vring_used { 124 __virtio16 flags; 125 __virtio16 idx; 126 vring_used_elem_t ring[]; 127 }; 128 129 /* 130 * The ring element addresses are passed between components with different 131 * alignments assumptions. Thus, we might need to decrease the compiler-selected 132 * alignment, and so must use a typedef to make sure the aligned attribute 133 * actually takes hold: 134 * 135 * https://gcc.gnu.org/onlinedocs//gcc/Common-Type-Attributes.html#Common-Type-Attributes 136 * 137 * When used on a struct, or struct member, the aligned attribute can only 138 * increase the alignment; in order to decrease it, the packed attribute must 139 * be specified as well. When used as part of a typedef, the aligned attribute 140 * can both increase and decrease alignment, and specifying the packed 141 * attribute generates a warning. 142 */ 143 typedef struct vring_desc __attribute__((aligned(VRING_DESC_ALIGN_SIZE))) 144 vring_desc_t; 145 typedef struct vring_avail __attribute__((aligned(VRING_AVAIL_ALIGN_SIZE))) 146 vring_avail_t; 147 typedef struct vring_used __attribute__((aligned(VRING_USED_ALIGN_SIZE))) 148 vring_used_t; 149 150 struct vring { 151 unsigned int num; 152 153 vring_desc_t *desc; 154 155 vring_avail_t *avail; 156 157 vring_used_t *used; 158 }; 159 160 #ifndef VIRTIO_RING_NO_LEGACY 161 162 /* The standard layout for the ring is a continuous chunk of memory which looks 163 * like this. We assume num is a power of 2. 164 * 165 * struct vring 166 * { 167 * // The actual descriptors (16 bytes each) 168 * struct vring_desc desc[num]; 169 * 170 * // A ring of available descriptor heads with free-running index. 171 * __virtio16 avail_flags; 172 * __virtio16 avail_idx; 173 * __virtio16 available[num]; 174 * __virtio16 used_event_idx; 175 * 176 * // Padding to the next align boundary. 177 * char pad[]; 178 * 179 * // A ring of used descriptor heads with free-running index. 180 * __virtio16 used_flags; 181 * __virtio16 used_idx; 182 * struct vring_used_elem used[num]; 183 * __virtio16 avail_event_idx; 184 * }; 185 */ 186 /* We publish the used event index at the end of the available ring, and vice 187 * versa. They are at the end for backwards compatibility. */ 188 #define vring_used_event(vr) ((vr)->avail->ring[(vr)->num]) 189 #define vring_avail_event(vr) (*(__virtio16 *)&(vr)->used->ring[(vr)->num]) 190 191 static inline void vring_init(struct vring *vr, unsigned int num, void *p, 192 unsigned long align) 193 { 194 vr->num = num; 195 vr->desc = p; 196 vr->avail = (struct vring_avail *)((char *)p + num * sizeof(struct vring_desc)); 197 vr->used = (void *)(((uintptr_t)&vr->avail->ring[num] + sizeof(__virtio16) 198 + align-1) & ~(align - 1)); 199 } 200 201 static inline unsigned vring_size(unsigned int num, unsigned long align) 202 { 203 return ((sizeof(struct vring_desc) * num + sizeof(__virtio16) * (3 + num) 204 + align - 1) & ~(align - 1)) 205 + sizeof(__virtio16) * 3 + sizeof(struct vring_used_elem) * num; 206 } 207 208 #endif /* VIRTIO_RING_NO_LEGACY */ 209 210 /* The following is used with USED_EVENT_IDX and AVAIL_EVENT_IDX */ 211 /* Assuming a given event_idx value from the other side, if 212 * we have just incremented index from old to new_idx, 213 * should we trigger an event? */ 214 static inline int vring_need_event(uint16_t event_idx, uint16_t new_idx, uint16_t old) 215 { 216 /* Note: Xen has similar logic for notification hold-off 217 * in include/xen/interface/io/ring.h with req_event and req_prod 218 * corresponding to event_idx + 1 and new_idx respectively. 219 * Note also that req_event and req_prod in Xen start at 1, 220 * event indexes in virtio start at 0. */ 221 return (uint16_t)(new_idx - event_idx - 1) < (uint16_t)(new_idx - old); 222 } 223 224 struct vring_packed_desc_event { 225 /* Descriptor Ring Change Event Offset/Wrap Counter. */ 226 uint16_t off_wrap; 227 /* Descriptor Ring Change Event Flags. */ 228 uint16_t flags; 229 }; 230 231 struct vring_packed_desc { 232 /* Buffer Address. */ 233 uint64_t addr; 234 /* Buffer Length. */ 235 uint32_t len; 236 /* Buffer ID. */ 237 uint16_t id; 238 /* The flags depending on descriptor type. */ 239 uint16_t flags; 240 }; 241 242 #endif /* _LINUX_VIRTIO_RING_H */ 243