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 vm_paddr_t desc_paddr; 93 vm_paddr_t avail_paddr; 94 vm_paddr_t used_paddr; 95 }; 96 97 /* Alignment requirements for vring elements. 98 * When using pre-virtio 1.0 layout, these fall out naturally. 99 */ 100 #define VRING_AVAIL_ALIGN_SIZE 2 101 #define VRING_USED_ALIGN_SIZE 4 102 #define VRING_DESC_ALIGN_SIZE 16 103 104 /* The standard layout for the ring is a continuous chunk of memory which 105 * looks like this. We assume num is a power of 2. 106 * 107 * struct vring { 108 * // The actual descriptors (16 bytes each) 109 * struct vring_desc desc[num]; 110 * 111 * // A ring of available descriptor heads with free-running index. 112 * __u16 avail_flags; 113 * __u16 avail_idx; 114 * __u16 available[num]; 115 * __u16 used_event_idx; 116 * 117 * // Padding to the next align boundary. 118 * char pad[]; 119 * 120 * // A ring of used descriptor heads with free-running index. 121 * __u16 used_flags; 122 * __u16 used_idx; 123 * struct vring_used_elem used[num]; 124 * __u16 avail_event_idx; 125 * }; 126 * 127 * NOTE: for VirtIO PCI, align is 4096. 128 */ 129 130 /* 131 * We publish the used event index at the end of the available ring, and vice 132 * versa. They are at the end for backwards compatibility. 133 */ 134 #define vring_used_event(vr) ((vr)->avail->ring[(vr)->num]) 135 #define vring_avail_event(vr) (*(uint16_t *)&(vr)->used->ring[(vr)->num]) 136 137 static inline int 138 vring_size(unsigned int num, unsigned long align) 139 { 140 int size; 141 142 size = num * sizeof(struct vring_desc); 143 size += sizeof(struct vring_avail) + (num * sizeof(uint16_t)) + 144 sizeof(uint16_t); 145 size = (size + align - 1) & ~(align - 1); 146 size += sizeof(struct vring_used) + 147 (num * sizeof(struct vring_used_elem)) + sizeof(uint16_t); 148 return (size); 149 } 150 151 static inline void 152 vring_init(struct vring *vr, unsigned int num, uint8_t *p, vm_paddr_t paddr, 153 unsigned long align) 154 { 155 unsigned long avail_offset; 156 unsigned long used_offset; 157 158 avail_offset = num * sizeof(struct vring_desc); 159 used_offset = (avail_offset + sizeof(struct vring_avail) + 160 sizeof(uint16_t) * num + align - 1) & ~(align - 1); 161 162 vr->num = num; 163 vr->desc = (struct vring_desc *) p; 164 vr->avail = (struct vring_avail *) (p + avail_offset); 165 vr->used = (struct vring_used *) (p + used_offset); 166 167 vr->desc_paddr = paddr; 168 vr->avail_paddr = paddr + avail_offset; 169 vr->used_paddr = paddr + used_offset; 170 } 171 172 /* 173 * The following is used with VIRTIO_RING_F_EVENT_IDX. 174 * 175 * Assuming a given event_idx value from the other size, if we have 176 * just incremented index from old to new_idx, should we trigger an 177 * event? 178 */ 179 static inline int 180 vring_need_event(uint16_t event_idx, uint16_t new_idx, uint16_t old) 181 { 182 183 return (uint16_t)(new_idx - event_idx - 1) < (uint16_t)(new_idx - old); 184 } 185 #endif /* VIRTIO_RING_H */ 186