1 /*- 2 * Copyright Rusty Russell IBM Corporation 2007. 3 * 4 * This header is BSD licensed so anyone can use the definitions to implement 5 * compatible drivers/servers. 6 * 7 * Redistribution and use in source and binary forms, with or without 8 * modification, are permitted provided that the following conditions 9 * are met: 10 * 1. Redistributions of source code must retain the above copyright 11 * notice, this list of conditions and the following disclaimer. 12 * 2. Redistributions in binary form must reproduce the above copyright 13 * notice, this list of conditions and the following disclaimer in the 14 * documentation and/or other materials provided with the distribution. 15 * 3. Neither the name of IBM nor the names of its contributors 16 * may be used to endorse or promote products derived from this software 17 * without specific prior written permission. 18 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 19 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED 20 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 21 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL IBM OR CONTRIBUTORS BE LIABLE 22 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 23 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 24 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 25 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 26 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 27 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 28 * SUCH DAMAGE. 29 * 30 * $FreeBSD: src/sys/dev/virtio/virtio_ring.h,v 1.3 2012/04/14 05:48:04 grehan Exp $ 31 */ 32 33 #ifndef VIRTIO_RING_H 34 #define VIRTIO_RING_H 35 36 #include <sys/types.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 /* The standard layout for the ring is a continuous chunk of memory which 96 * looks like this. We assume num is a power of 2. 97 * 98 * struct vring { 99 * // The actual descriptors (16 bytes each) 100 * struct vring_desc desc[num]; 101 * 102 * // A ring of available descriptor heads with free-running index. 103 * __u16 avail_flags; 104 * __u16 avail_idx; 105 * __u16 available[num]; 106 * __u16 used_event_idx; 107 * 108 * // Padding to the next align boundary. 109 * char pad[]; 110 * 111 * // A ring of used descriptor heads with free-running index. 112 * __u16 used_flags; 113 * __u16 used_idx; 114 * struct vring_used_elem used[num]; 115 * __u16 avail_event_idx; 116 * }; 117 * 118 * NOTE: for VirtIO PCI, align is 4096. 119 */ 120 121 /* 122 * We publish the used event index at the end of the available ring, and vice 123 * versa. They are at the end for backwards compatibility. 124 */ 125 #define vring_used_event(vr) ((vr)->avail->ring[(vr)->num]) 126 #define vring_avail_event(vr) (*(uint16_t *)&(vr)->used->ring[(vr)->num]) 127 128 static inline int 129 vring_size(unsigned int num, unsigned long align) 130 { 131 int size; 132 133 size = num * sizeof(struct vring_desc); 134 size += sizeof(struct vring_avail) + (num * sizeof(uint16_t)); 135 size = roundup2(size, align); 136 size += sizeof(struct vring_used) + 137 (num * sizeof(struct vring_used_elem)); 138 return (size); 139 } 140 141 static inline void 142 vring_init(struct vring *vr, unsigned int num, uint8_t *p, 143 unsigned long align) 144 { 145 vr->num = num; 146 vr->desc = (struct vring_desc *) p; 147 vr->avail = (struct vring_avail *) (p + 148 num * sizeof(struct vring_desc)); 149 vr->used = 150 (void *)roundup2((unsigned long)&vr->avail->ring[num], align); 151 } 152 153 /* 154 * The following is used with VIRTIO_RING_F_EVENT_IDX. 155 * 156 * Assuming a given event_idx value from the other size, if we have 157 * just incremented index from old to new_idx, should we trigger an 158 * event? 159 */ 160 static inline int 161 vring_need_event(uint16_t event_idx, uint16_t new_idx, uint16_t old) 162 { 163 164 return (uint16_t)(new_idx - event_idx - 1) < (uint16_t)(new_idx - old); 165 } 166 #endif /* VIRTIO_RING_H */ 167