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