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. 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 #ifndef __KERNEL__ 35 #include <stdint.h> 36 #endif 37 #include <linux/types.h> 38 #include <linux/virtio_types.h> 39 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 46 47 /* 48 * Mark a descriptor as available or used in packed ring. 49 * Notice: they are defined as shifts instead of shifted values. 50 */ 51 #define VRING_PACKED_DESC_F_AVAIL 7 52 #define VRING_PACKED_DESC_F_USED 15 53 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 60 * optimization. */ 61 #define VRING_AVAIL_F_NO_INTERRUPT 1 62 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 67 /* 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. 71 */ 72 #define VRING_PACKED_EVENT_FLAG_DESC 0x2 73 74 /* 75 * Wrap counter bit shift in event suppression structure 76 * of packed ring. 77 */ 78 #define VRING_PACKED_EVENT_F_WRAP_CTR 15 79 80 /* We support indirect buffer descriptors */ 81 #define VIRTIO_RING_F_INDIRECT_DESC 28 82 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 88 89 /* Virtio ring descriptors: 16 bytes. These can chain together via "next". */ 90 struct vring_desc { 91 /* Address (guest-physical). */ 92 __virtio64 addr; 93 /* Length. */ 94 __virtio32 len; 95 /* The flags as indicated above. */ 96 __virtio16 flags; 97 /* We chain unused descriptors via this, too */ 98 __virtio16 next; 99 }; 100 101 struct vring_avail { 102 __virtio16 flags; 103 __virtio16 idx; 104 __virtio16 ring[]; 105 }; 106 107 /* u32 is used here for ids for padding reasons. */ 108 struct vring_used_elem { 109 /* Index of start of used descriptor chain. */ 110 __virtio32 id; 111 /* Total length of the descriptor chain which was used (written to) */ 112 __virtio32 len; 113 }; 114 115 struct vring_used { 116 __virtio16 flags; 117 __virtio16 idx; 118 struct vring_used_elem ring[]; 119 }; 120 121 struct vring { 122 unsigned int num; 123 124 struct vring_desc *desc; 125 126 struct vring_avail *avail; 127 128 struct vring_used *used; 129 }; 130 131 /* Alignment requirements for vring elements. 132 * When using pre-virtio 1.0 layout, these fall out naturally. 133 */ 134 #define VRING_AVAIL_ALIGN_SIZE 2 135 #define VRING_USED_ALIGN_SIZE 4 136 #define VRING_DESC_ALIGN_SIZE 16 137 138 /* The standard layout for the ring is a continuous chunk of memory which looks 139 * like this. We assume num is a power of 2. 140 * 141 * struct vring 142 * { 143 * // The actual descriptors (16 bytes each) 144 * struct vring_desc desc[num]; 145 * 146 * // A ring of available descriptor heads with free-running index. 147 * __virtio16 avail_flags; 148 * __virtio16 avail_idx; 149 * __virtio16 available[num]; 150 * __virtio16 used_event_idx; 151 * 152 * // Padding to the next align boundary. 153 * char pad[]; 154 * 155 * // A ring of used descriptor heads with free-running index. 156 * __virtio16 used_flags; 157 * __virtio16 used_idx; 158 * struct vring_used_elem used[num]; 159 * __virtio16 avail_event_idx; 160 * }; 161 */ 162 /* We publish the used event index at the end of the available ring, and vice 163 * versa. They are at the end for backwards compatibility. */ 164 #define vring_used_event(vr) ((vr)->avail->ring[(vr)->num]) 165 #define vring_avail_event(vr) (*(__virtio16 *)&(vr)->used->ring[(vr)->num]) 166 167 static inline void vring_init(struct vring *vr, unsigned int num, void *p, 168 unsigned long align) 169 { 170 vr->num = num; 171 vr->desc = p; 172 vr->avail = p + num*sizeof(struct vring_desc); 173 vr->used = (void *)(((uintptr_t)&vr->avail->ring[num] + sizeof(__virtio16) 174 + align-1) & ~(align - 1)); 175 } 176 177 static inline unsigned vring_size(unsigned int num, unsigned long align) 178 { 179 return ((sizeof(struct vring_desc) * num + sizeof(__virtio16) * (3 + num) 180 + align - 1) & ~(align - 1)) 181 + sizeof(__virtio16) * 3 + sizeof(struct vring_used_elem) * num; 182 } 183 184 /* The following is used with USED_EVENT_IDX and AVAIL_EVENT_IDX */ 185 /* Assuming a given event_idx value from the other side, if 186 * we have just incremented index from old to new_idx, 187 * should we trigger an event? */ 188 static inline int vring_need_event(__u16 event_idx, __u16 new_idx, __u16 old) 189 { 190 /* Note: Xen has similar logic for notification hold-off 191 * in include/xen/interface/io/ring.h with req_event and req_prod 192 * corresponding to event_idx + 1 and new_idx respectively. 193 * Note also that req_event and req_prod in Xen start at 1, 194 * event indexes in virtio start at 0. */ 195 return (__u16)(new_idx - event_idx - 1) < (__u16)(new_idx - old); 196 } 197 198 struct vring_packed_desc_event { 199 /* Descriptor Ring Change Event Offset/Wrap Counter. */ 200 __le16 off_wrap; 201 /* Descriptor Ring Change Event Flags. */ 202 __le16 flags; 203 }; 204 205 struct vring_packed_desc { 206 /* Buffer Address. */ 207 __le64 addr; 208 /* Buffer Length. */ 209 __le32 len; 210 /* Buffer ID. */ 211 __le16 id; 212 /* The flags depending on descriptor type. */ 213 __le16 flags; 214 }; 215 216 struct vring_packed { 217 unsigned int num; 218 219 struct vring_packed_desc *desc; 220 221 struct vring_packed_desc_event *driver; 222 223 struct vring_packed_desc_event *device; 224 }; 225 226 #endif /* _UAPI_LINUX_VIRTIO_RING_H */ 227