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 33 #ifndef VIRTIO_RING_H 34 #define VIRTIO_RING_H 35 36 /* This marks a buffer as continuing via the next field. */ 37 #define VRING_DESC_F_NEXT 1 38 /* This marks a buffer as write-only (otherwise read-only). */ 39 #define VRING_DESC_F_WRITE 2 40 /* This means the buffer contains a list of buffer descriptors. */ 41 #define VRING_DESC_F_INDIRECT 4 42 43 /* The Host uses this in used->flags to advise the Guest: don't kick me 44 * when you add a buffer. It's unreliable, so it's simply an 45 * optimization. Guest will still kick if it's out of buffers. */ 46 #define VRING_USED_F_NO_NOTIFY 1 47 /* The Guest uses this in avail->flags to advise the Host: don't 48 * interrupt me when you consume a buffer. It's unreliable, so it's 49 * simply an optimization. */ 50 #define VRING_AVAIL_F_NO_INTERRUPT 1 51 52 /* VirtIO ring descriptors: 16 bytes. 53 * These can chain together via "next". */ 54 struct vring_desc { 55 /* Address (guest-physical). */ 56 uint64_t addr; 57 /* Length. */ 58 uint32_t len; 59 /* The flags as indicated above. */ 60 uint16_t flags; 61 /* We chain unused descriptors via this, too. */ 62 uint16_t next; 63 }; 64 65 struct vring_avail { 66 uint16_t flags; 67 uint16_t idx; 68 uint16_t ring[0]; 69 }; 70 71 /* uint32_t is used here for ids for padding reasons. */ 72 struct vring_used_elem { 73 /* Index of start of used descriptor chain. */ 74 uint32_t id; 75 /* Total length of the descriptor chain which was written to. */ 76 uint32_t len; 77 }; 78 79 struct vring_used { 80 uint16_t flags; 81 uint16_t idx; 82 struct vring_used_elem ring[0]; 83 }; 84 85 struct vring { 86 unsigned int num; 87 88 struct vring_desc *desc; 89 struct vring_avail *avail; 90 struct vring_used *used; 91 }; 92 93 /* Alignment requirements for vring elements. 94 * When using pre-virtio 1.0 layout, these fall out naturally. 95 */ 96 #define VRING_AVAIL_ALIGN_SIZE 2 97 #define VRING_USED_ALIGN_SIZE 4 98 #define VRING_DESC_ALIGN_SIZE 16 99 100 /* The standard layout for the ring is a continuous chunk of memory which 101 * looks like this. We assume num is a power of 2. 102 * 103 * struct vring { 104 * // The actual descriptors (16 bytes each) 105 * struct vring_desc desc[num]; 106 * 107 * // A ring of available descriptor heads with free-running index. 108 * __u16 avail_flags; 109 * __u16 avail_idx; 110 * __u16 available[num]; 111 * __u16 used_event_idx; 112 * 113 * // Padding to the next align boundary. 114 * char pad[]; 115 * 116 * // A ring of used descriptor heads with free-running index. 117 * __u16 used_flags; 118 * __u16 used_idx; 119 * struct vring_used_elem used[num]; 120 * __u16 avail_event_idx; 121 * }; 122 * 123 * NOTE: for VirtIO PCI, align is 4096. 124 */ 125 126 /* 127 * We publish the used event index at the end of the available ring, and vice 128 * versa. They are at the end for backwards compatibility. 129 */ 130 #define vring_used_event(vr) ((vr)->avail->ring[(vr)->num]) 131 #define vring_avail_event(vr) (*(uint16_t *)&(vr)->used->ring[(vr)->num]) 132 133 static inline int 134 vring_size(unsigned int num, unsigned long align) 135 { 136 int size; 137 138 size = num * sizeof(struct vring_desc); 139 size += sizeof(struct vring_avail) + (num * sizeof(uint16_t)) + 140 sizeof(uint16_t); 141 size = (size + align - 1) & ~(align - 1); 142 size += sizeof(struct vring_used) + 143 (num * sizeof(struct vring_used_elem)) + sizeof(uint16_t); 144 return (size); 145 } 146 147 static inline void 148 vring_init(struct vring *vr, unsigned int num, uint8_t *p, 149 unsigned long align) 150 { 151 vr->num = num; 152 vr->desc = (struct vring_desc *) p; 153 vr->avail = (struct vring_avail *) (p + 154 num * sizeof(struct vring_desc)); 155 vr->used = (void *) 156 (((unsigned long) &vr->avail->ring[num] + align-1) & ~(align-1)); 157 } 158 159 /* 160 * The following is used with VIRTIO_RING_F_EVENT_IDX. 161 * 162 * Assuming a given event_idx value from the other size, if we have 163 * just incremented index from old to new_idx, should we trigger an 164 * event? 165 */ 166 static inline int 167 vring_need_event(uint16_t event_idx, uint16_t new_idx, uint16_t old) 168 { 169 170 return (uint16_t)(new_idx - event_idx - 1) < (uint16_t)(new_idx - old); 171 } 172 #endif /* VIRTIO_RING_H */ 173