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 /* Alignment requirements for vring elements. 90 * When using pre-virtio 1.0 layout, these fall out naturally. 91 */ 92 #define VRING_AVAIL_ALIGN_SIZE 2 93 #define VRING_USED_ALIGN_SIZE 4 94 #define VRING_DESC_ALIGN_SIZE 16 95 96 /** 97 * struct vring_desc - Virtio ring descriptors, 98 * 16 bytes long. These can chain together via @next. 99 * 100 * @addr: buffer address (guest-physical) 101 * @len: buffer length 102 * @flags: descriptor flags 103 * @next: index of the next descriptor in the chain, 104 * if the VRING_DESC_F_NEXT flag is set. We chain unused 105 * descriptors via this, too. 106 */ 107 struct vring_desc { 108 __virtio64 addr; 109 __virtio32 len; 110 __virtio16 flags; 111 __virtio16 next; 112 }; 113 114 struct vring_avail { 115 __virtio16 flags; 116 __virtio16 idx; 117 __virtio16 ring[]; 118 }; 119 120 /* u32 is used here for ids for padding reasons. */ 121 struct vring_used_elem { 122 /* Index of start of used descriptor chain. */ 123 __virtio32 id; 124 /* Total length of the descriptor chain which was used (written to) */ 125 __virtio32 len; 126 }; 127 128 typedef struct vring_used_elem __attribute__((aligned(VRING_USED_ALIGN_SIZE))) 129 vring_used_elem_t; 130 131 struct vring_used { 132 __virtio16 flags; 133 __virtio16 idx; 134 vring_used_elem_t ring[]; 135 }; 136 137 /* 138 * The ring element addresses are passed between components with different 139 * alignments assumptions. Thus, we might need to decrease the compiler-selected 140 * alignment, and so must use a typedef to make sure the aligned attribute 141 * actually takes hold: 142 * 143 * https://gcc.gnu.org/onlinedocs//gcc/Common-Type-Attributes.html#Common-Type-Attributes 144 * 145 * When used on a struct, or struct member, the aligned attribute can only 146 * increase the alignment; in order to decrease it, the packed attribute must 147 * be specified as well. When used as part of a typedef, the aligned attribute 148 * can both increase and decrease alignment, and specifying the packed 149 * attribute generates a warning. 150 */ 151 typedef struct vring_desc __attribute__((aligned(VRING_DESC_ALIGN_SIZE))) 152 vring_desc_t; 153 typedef struct vring_avail __attribute__((aligned(VRING_AVAIL_ALIGN_SIZE))) 154 vring_avail_t; 155 typedef struct vring_used __attribute__((aligned(VRING_USED_ALIGN_SIZE))) 156 vring_used_t; 157 158 struct vring { 159 unsigned int num; 160 161 vring_desc_t *desc; 162 163 vring_avail_t *avail; 164 165 vring_used_t *used; 166 }; 167 168 #ifndef VIRTIO_RING_NO_LEGACY 169 170 /* The standard layout for the ring is a continuous chunk of memory which looks 171 * like this. We assume num is a power of 2. 172 * 173 * struct vring 174 * { 175 * // The actual descriptors (16 bytes each) 176 * struct vring_desc desc[num]; 177 * 178 * // A ring of available descriptor heads with free-running index. 179 * __virtio16 avail_flags; 180 * __virtio16 avail_idx; 181 * __virtio16 available[num]; 182 * __virtio16 used_event_idx; 183 * 184 * // Padding to the next align boundary. 185 * char pad[]; 186 * 187 * // A ring of used descriptor heads with free-running index. 188 * __virtio16 used_flags; 189 * __virtio16 used_idx; 190 * struct vring_used_elem used[num]; 191 * __virtio16 avail_event_idx; 192 * }; 193 */ 194 /* We publish the used event index at the end of the available ring, and vice 195 * versa. They are at the end for backwards compatibility. */ 196 #define vring_used_event(vr) ((vr)->avail->ring[(vr)->num]) 197 #define vring_avail_event(vr) (*(__virtio16 *)&(vr)->used->ring[(vr)->num]) 198 199 static inline void vring_init(struct vring *vr, unsigned int num, void *p, 200 unsigned long align) 201 { 202 vr->num = num; 203 vr->desc = p; 204 vr->avail = (struct vring_avail *)((char *)p + num * sizeof(struct vring_desc)); 205 vr->used = (void *)(((uintptr_t)&vr->avail->ring[num] + sizeof(__virtio16) 206 + align-1) & ~(align - 1)); 207 } 208 209 static inline unsigned vring_size(unsigned int num, unsigned long align) 210 { 211 return ((sizeof(struct vring_desc) * num + sizeof(__virtio16) * (3 + num) 212 + align - 1) & ~(align - 1)) 213 + sizeof(__virtio16) * 3 + sizeof(struct vring_used_elem) * num; 214 } 215 216 #endif /* VIRTIO_RING_NO_LEGACY */ 217 218 /* The following is used with USED_EVENT_IDX and AVAIL_EVENT_IDX */ 219 /* Assuming a given event_idx value from the other side, if 220 * we have just incremented index from old to new_idx, 221 * should we trigger an event? */ 222 static inline int vring_need_event(__u16 event_idx, __u16 new_idx, __u16 old) 223 { 224 /* Note: Xen has similar logic for notification hold-off 225 * in include/xen/interface/io/ring.h with req_event and req_prod 226 * corresponding to event_idx + 1 and new_idx respectively. 227 * Note also that req_event and req_prod in Xen start at 1, 228 * event indexes in virtio start at 0. */ 229 return (__u16)(new_idx - event_idx - 1) < (__u16)(new_idx - old); 230 } 231 232 struct vring_packed_desc_event { 233 /* Descriptor Ring Change Event Offset/Wrap Counter. */ 234 __le16 off_wrap; 235 /* Descriptor Ring Change Event Flags. */ 236 __le16 flags; 237 }; 238 239 struct vring_packed_desc { 240 /* Buffer Address. */ 241 __le64 addr; 242 /* Buffer Length. */ 243 __le32 len; 244 /* Buffer ID. */ 245 __le16 id; 246 /* The flags depending on descriptor type. */ 247 __le16 flags; 248 }; 249 250 #endif /* _UAPI_LINUX_VIRTIO_RING_H */ 251