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 22 '' AND 23 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 24 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 25 * ARE DISCLAIMED. IN NO EVENT SHALL IBM OR CONTRIBUTORS BE LIABLE 26 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 27 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 28 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 29 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 30 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 31 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 32 * SUCH DAMAGE. 33 * 34 * Copyright Rusty Russell IBM Corporation 2007. */ 35 #ifndef __KERNEL__ 36 #include <stdint.h> 37 #endif 38 #include <linux/types.h> 39 #include <linux/virtio_types.h> 40 41 /* This marks a buffer as continuing via the next field. */ 42 #define VRING_DESC_F_NEXT 1 43 /* This marks a buffer as write-only (otherwise read-only). */ 44 #define VRING_DESC_F_WRITE 2 45 /* This means the buffer contains a list of buffer descriptors. */ 46 #define VRING_DESC_F_INDIRECT 4 47 48 /* 49 * Mark a descriptor as available or used in packed ring. 50 * Notice: they are defined as shifts instead of shifted values. 51 */ 52 #define VRING_PACKED_DESC_F_AVAIL 7 53 #define VRING_PACKED_DESC_F_USED 15 54 55 /* The Host uses this in used->flags to advise the Guest: don't kick me when 56 * you add a buffer. It's unreliable, so it's simply an optimization. Guest 57 * will still kick if it's out of buffers. */ 58 #define VRING_USED_F_NO_NOTIFY 1 59 /* The Guest uses this in avail->flags to advise the Host: don't interrupt me 60 * when you consume a buffer. It's unreliable, so it's simply an 61 * optimization. */ 62 #define VRING_AVAIL_F_NO_INTERRUPT 1 63 64 /* Enable events in packed ring. */ 65 #define VRING_PACKED_EVENT_FLAG_ENABLE 0x0 66 /* Disable events in packed ring. */ 67 #define VRING_PACKED_EVENT_FLAG_DISABLE 0x1 68 /* 69 * Enable events for a specific descriptor in packed ring. 70 * (as specified by Descriptor Ring Change Event Offset/Wrap Counter). 71 * Only valid if VIRTIO_RING_F_EVENT_IDX has been negotiated. 72 */ 73 #define VRING_PACKED_EVENT_FLAG_DESC 0x2 74 75 /* 76 * Wrap counter bit shift in event suppression structure 77 * of packed ring. 78 */ 79 #define VRING_PACKED_EVENT_F_WRAP_CTR 15 80 81 /* We support indirect buffer descriptors */ 82 #define VIRTIO_RING_F_INDIRECT_DESC 28 83 84 /* The Guest publishes the used index for which it expects an interrupt 85 * at the end of the avail ring. Host should ignore the avail->flags field. */ 86 /* The Host publishes the avail index for which it expects a kick 87 * at the end of the used ring. Guest should ignore the used->flags field. */ 88 #define VIRTIO_RING_F_EVENT_IDX 29 89 90 /* Virtio ring descriptors: 16 bytes. These can chain together via "next". */ 91 struct vring_desc { 92 /* Address (guest-physical). */ 93 __virtio64 addr; 94 /* Length. */ 95 __virtio32 len; 96 /* The flags as indicated above. */ 97 __virtio16 flags; 98 /* We chain unused descriptors via this, too */ 99 __virtio16 next; 100 }; 101 102 struct vring_avail { 103 __virtio16 flags; 104 __virtio16 idx; 105 __virtio16 ring[]; 106 }; 107 108 /* u32 is used here for ids for padding reasons. */ 109 struct vring_used_elem { 110 /* Index of start of used descriptor chain. */ 111 __virtio32 id; 112 /* Total length of the descriptor chain which was used (written to) */ 113 __virtio32 len; 114 }; 115 116 struct vring_used { 117 __virtio16 flags; 118 __virtio16 idx; 119 struct vring_used_elem ring[]; 120 }; 121 122 struct vring { 123 unsigned int num; 124 125 struct vring_desc *desc; 126 127 struct vring_avail *avail; 128 129 struct vring_used *used; 130 }; 131 132 /* Alignment requirements for vring elements. 133 * When using pre-virtio 1.0 layout, these fall out naturally. 134 */ 135 #define VRING_AVAIL_ALIGN_SIZE 2 136 #define VRING_USED_ALIGN_SIZE 4 137 #define VRING_DESC_ALIGN_SIZE 16 138 139 /* The standard layout for the ring is a continuous chunk of memory which looks 140 * like this. We assume num is a power of 2. 141 * 142 * struct vring 143 * { 144 * The actual descriptors (16 bytes each) 145 * struct vring_desc desc[num]; 146 * 147 * A ring of available descriptor heads with free-running index. 148 * __virtio16 avail_flags; 149 * __virtio16 avail_idx; 150 * __virtio16 available[num]; 151 * __virtio16 used_event_idx; 152 * 153 * Padding to the next align boundary. 154 * char pad[]; 155 * 156 * A ring of used descriptor heads with free-running index. 157 * __virtio16 used_flags; 158 * __virtio16 used_idx; 159 * struct vring_used_elem used[num]; 160 * __virtio16 avail_event_idx; 161 * }; 162 */ 163 /* We publish the used event index at the end of the available ring, and vice 164 * versa. They are at the end for backwards compatibility. */ 165 #define vring_used_event(vr) ((vr)->avail->ring[(vr)->num]) 166 #define vring_avail_event(vr) (*(__virtio16 *)&(vr)->used->ring[(vr)->num]) 167 168 static inline void 169 vring_init(struct vring *vr, unsigned int num, void *p, 170 unsigned long align) 171 { 172 vr->num = num; 173 vr->desc = p; 174 vr->avail = (struct vring_avail *)((char *)p + num * sizeof(struct vring_desc 175 )); 176 vr->used = (void *)(((uintptr_t)&vr->avail->ring[num] + sizeof(__virtio16) 177 + align - 1) & ~(align - 1)); 178 } 179 180 static inline unsigned 181 vring_size(unsigned int num, unsigned long align) 182 { 183 return ((sizeof(struct vring_desc) * num + sizeof(__virtio16) * (3 + num) 184 + align - 1) & ~(align - 1)) 185 + sizeof(__virtio16) * 3 + sizeof(struct vring_used_elem) * num; 186 } 187 188 /* The following is used with USED_EVENT_IDX and AVAIL_EVENT_IDX */ 189 /* Assuming a given event_idx value from the other side, if 190 * we have just incremented index from old to new_idx, 191 * should we trigger an event? */ 192 static inline int 193 vring_need_event(__u16 event_idx, __u16 new_idx, __u16 old) 194 { 195 /* Note: Xen has similar logic for notification hold-off 196 * in include/xen/interface/io/ring.h with req_event and req_prod 197 * corresponding to event_idx + 1 and new_idx respectively. 198 * Note also that req_event and req_prod in Xen start at 1, 199 * event indexes in virtio start at 0. */ 200 return (__u16)(new_idx - event_idx - 1) < (__u16)(new_idx - old); 201 } 202 203 struct vring_packed_desc_event { 204 /* Descriptor Ring Change Event Offset/Wrap Counter. */ 205 __le16 off_wrap; 206 /* Descriptor Ring Change Event Flags. */ 207 __le16 flags; 208 }; 209 210 struct vring_packed_desc { 211 /* Buffer Address. */ 212 __le64 addr; 213 /* Buffer Length. */ 214 __le32 len; 215 /* Buffer ID. */ 216 __le16 id; 217 /* The flags depending on descriptor type. */ 218 __le16 flags; 219 }; 220 221 #endif /* _LINUX_VIRTIO_RING_H */ 222