1 /*- 2 * SPDX-License-Identifier: BSD-3-Clause 3 * 4 * Copyright Rusty Russell IBM Corporation 2007. 5 * 6 * This header is BSD licensed so anyone can use the definitions to implement 7 * compatible drivers/servers. 8 * 9 * Redistribution and use in source and binary forms, with or without 10 * modification, are permitted provided that the following conditions 11 * are met: 12 * 1. Redistributions of source code must retain the above copyright 13 * notice, this list of conditions and the following disclaimer. 14 * 2. Redistributions in binary form must reproduce the above copyright 15 * notice, this list of conditions and the following disclaimer in the 16 * documentation and/or other materials provided with the distribution. 17 * 3. Neither the name of IBM nor the names of its contributors 18 * may be used to endorse or promote products derived from this software 19 * without specific prior written permission. 20 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 21 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED 22 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 23 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL IBM OR CONTRIBUTORS BE LIABLE 24 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30 * SUCH DAMAGE. 31 * 32 * $FreeBSD$ 33 */ 34 35 #ifndef VIRTIO_RING_H 36 #define VIRTIO_RING_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 /* The Host uses this in used->flags to advise the Guest: don't kick me 46 * when you add a buffer. It's unreliable, so it's simply an 47 * optimization. Guest will still kick if it's out of buffers. */ 48 #define VRING_USED_F_NO_NOTIFY 1 49 /* The Guest uses this in avail->flags to advise the Host: don't 50 * interrupt me when you consume a buffer. It's unreliable, so it's 51 * simply an optimization. */ 52 #define VRING_AVAIL_F_NO_INTERRUPT 1 53 54 /* VirtIO ring descriptors: 16 bytes. 55 * These can chain together via "next". */ 56 struct vring_desc { 57 /* Address (guest-physical). */ 58 uint64_t addr; 59 /* Length. */ 60 uint32_t len; 61 /* The flags as indicated above. */ 62 uint16_t flags; 63 /* We chain unused descriptors via this, too. */ 64 uint16_t next; 65 }; 66 67 struct vring_avail { 68 uint16_t flags; 69 uint16_t idx; 70 uint16_t ring[0]; 71 }; 72 73 /* uint32_t is used here for ids for padding reasons. */ 74 struct vring_used_elem { 75 /* Index of start of used descriptor chain. */ 76 uint32_t id; 77 /* Total length of the descriptor chain which was written to. */ 78 uint32_t len; 79 }; 80 81 struct vring_used { 82 uint16_t flags; 83 uint16_t idx; 84 struct vring_used_elem ring[0]; 85 }; 86 87 struct vring { 88 unsigned int num; 89 90 struct vring_desc *desc; 91 struct vring_avail *avail; 92 struct vring_used *used; 93 }; 94 95 /* Alignment requirements for vring elements. 96 * When using pre-virtio 1.0 layout, these fall out naturally. 97 */ 98 #define VRING_AVAIL_ALIGN_SIZE 2 99 #define VRING_USED_ALIGN_SIZE 4 100 #define VRING_DESC_ALIGN_SIZE 16 101 102 /* The standard layout for the ring is a continuous chunk of memory which 103 * looks like this. We assume num is a power of 2. 104 * 105 * struct vring { 106 * // The actual descriptors (16 bytes each) 107 * struct vring_desc desc[num]; 108 * 109 * // A ring of available descriptor heads with free-running index. 110 * __u16 avail_flags; 111 * __u16 avail_idx; 112 * __u16 available[num]; 113 * __u16 used_event_idx; 114 * 115 * // Padding to the next align boundary. 116 * char pad[]; 117 * 118 * // A ring of used descriptor heads with free-running index. 119 * __u16 used_flags; 120 * __u16 used_idx; 121 * struct vring_used_elem used[num]; 122 * __u16 avail_event_idx; 123 * }; 124 * 125 * NOTE: for VirtIO PCI, align is 4096. 126 */ 127 128 /* 129 * We publish the used event index at the end of the available ring, and vice 130 * versa. They are at the end for backwards compatibility. 131 */ 132 #define vring_used_event(vr) ((vr)->avail->ring[(vr)->num]) 133 #define vring_avail_event(vr) (*(uint16_t *)&(vr)->used->ring[(vr)->num]) 134 135 static inline int 136 vring_size(unsigned int num, unsigned long align) 137 { 138 int size; 139 140 size = num * sizeof(struct vring_desc); 141 size += sizeof(struct vring_avail) + (num * sizeof(uint16_t)) + 142 sizeof(uint16_t); 143 size = (size + align - 1) & ~(align - 1); 144 size += sizeof(struct vring_used) + 145 (num * sizeof(struct vring_used_elem)) + sizeof(uint16_t); 146 return (size); 147 } 148 149 static inline void 150 vring_init(struct vring *vr, unsigned int num, uint8_t *p, 151 unsigned long align) 152 { 153 vr->num = num; 154 vr->desc = (struct vring_desc *) p; 155 vr->avail = (struct vring_avail *) (p + 156 num * sizeof(struct vring_desc)); 157 vr->used = (void *) 158 (((unsigned long) &vr->avail->ring[num] + align-1) & ~(align-1)); 159 } 160 161 /* 162 * The following is used with VIRTIO_RING_F_EVENT_IDX. 163 * 164 * Assuming a given event_idx value from the other size, if we have 165 * just incremented index from old to new_idx, should we trigger an 166 * event? 167 */ 168 static inline int 169 vring_need_event(uint16_t event_idx, uint16_t new_idx, uint16_t old) 170 { 171 172 return (uint16_t)(new_idx - event_idx - 1) < (uint16_t)(new_idx - old); 173 } 174 #endif /* VIRTIO_RING_H */ 175