1#ifndef _VIRTIO_RING_H 2#define _VIRTIO_RING_H 3/* An interface for efficient virtio implementation, currently for use by KVM 4 * and lguest, but hopefully others soon. Do NOT change this since it will 5 * break existing servers and clients. 6 * 7 * This header is BSD licensed so anyone can use the definitions to implement 8 * compatible drivers/servers. 9 * 10 * Redistribution and use in source and binary forms, with or without 11 * modification, are permitted provided that the following conditions 12 * are met: 13 * 1. Redistributions of source code must retain the above copyright 14 * notice, this list of conditions and the following disclaimer. 15 * 2. Redistributions in binary form must reproduce the above copyright 16 * notice, this list of conditions and the following disclaimer in the 17 * documentation and/or other materials provided with the distribution. 18 * 3. Neither the name of IBM nor the names of its contributors 19 * may be used to endorse or promote products derived from this software 20 * without specific prior written permission. 21 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS ``AS IS'' AND 22 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 23 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 24 * ARE DISCLAIMED. IN NO EVENT SHALL IBM OR CONTRIBUTORS BE LIABLE 25 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 26 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 27 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 28 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 29 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 30 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 31 * SUCH DAMAGE. 32 * 33 * Copyright Rusty Russell IBM Corporation 2007. */ 34#include <stdint.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 when 44 * you add a buffer. It's unreliable, so it's simply an optimization. Guest 45 * 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 interrupt me 48 * when you consume a buffer. It's unreliable, so it's simply an 49 * optimization. */ 50#define VRING_AVAIL_F_NO_INTERRUPT 1 51 52/* We support indirect buffer descriptors */ 53#define VIRTIO_RING_F_INDIRECT_DESC 28 54 55/* The Guest publishes the used index for which it expects an interrupt 56 * at the end of the avail ring. Host should ignore the avail->flags field. */ 57/* The Host publishes the avail index for which it expects a kick 58 * at the end of the used ring. Guest should ignore the used->flags field. */ 59#define VIRTIO_RING_F_EVENT_IDX 29 60 61/* Virtio ring descriptors: 16 bytes. These can chain together via "next". */ 62struct vring_desc { 63 /* Address (guest-physical). */ 64 uint64_t addr; 65 /* Length. */ 66 uint32_t len; 67 /* The flags as indicated above. */ 68 uint16_t flags; 69 /* We chain unused descriptors via this, too */ 70 uint16_t next; 71}; 72 73struct vring_avail { 74 uint16_t flags; 75 uint16_t idx; 76 uint16_t ring[]; 77}; 78 79/* u32 is used here for ids for padding reasons. */ 80struct vring_used_elem { 81 /* Index of start of used descriptor chain. */ 82 uint32_t id; 83 /* Total length of the descriptor chain which was used (written to) */ 84 uint32_t len; 85}; 86 87struct vring_used { 88 uint16_t flags; 89 uint16_t idx; 90 struct vring_used_elem ring[]; 91}; 92 93struct vring { 94 unsigned int num; 95 96 struct vring_desc *desc; 97 98 struct vring_avail *avail; 99 100 struct vring_used *used; 101}; 102 103/* The standard layout for the ring is a continuous chunk of memory which looks 104 * like this. We assume num is a power of 2. 105 * 106 * struct vring 107 * { 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 * uint16_t avail_flags; 113 * uint16_t avail_idx; 114 * uint16_t available[num]; 115 * uint16_t 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 * uint16_t used_flags; 122 * uint16_t used_idx; 123 * struct vring_used_elem used[num]; 124 * uint16_t avail_event_idx; 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#define vring_used_event(vr) ((vr)->avail->ring[(vr)->num]) 130#define vring_avail_event(vr) (*(uint16_t *)&(vr)->used->ring[(vr)->num]) 131 132static inline void vring_init(struct vring *vr, unsigned int num, void *p, 133 unsigned long align) 134{ 135 vr->num = num; 136 vr->desc = (struct vring_desc *)p; 137 vr->avail = (struct vring_avail *)((uint8_t*)p + num*sizeof(struct vring_desc)); 138 vr->used = (struct vring_used *)(((unsigned long)&vr->avail->ring[num] + sizeof(uint16_t) 139 + align-1) & ~(align - 1)); 140} 141 142static inline unsigned vring_size(unsigned int num, unsigned long align) 143{ 144 return ((sizeof(struct vring_desc) * num + sizeof(uint16_t) * (3 + num) 145 + align - 1) & ~(align - 1)) 146 + sizeof(uint16_t) * 3 + sizeof(struct vring_used_elem) * num; 147} 148 149/* The following is used with USED_EVENT_IDX and AVAIL_EVENT_IDX */ 150/* Assuming a given event_idx value from the other size, if 151 * we have just incremented index from old to new_idx, 152 * should we trigger an event? */ 153static inline int vring_need_event(uint16_t event_idx, uint16_t new_idx, uint16_t old) 154{ 155 /* Note: Xen has similar logic for notification hold-off 156 * in include/xen/interface/io/ring.h with req_event and req_prod 157 * corresponding to event_idx + 1 and new_idx respectively. 158 * Note also that req_event and req_prod in Xen start at 1, 159 * event indexes in virtio start at 0. */ 160 return (uint16_t)(new_idx - event_idx - 1) < (uint16_t)(new_idx - old); 161} 162 163#endif /* _VIRTIO_RING_H */ 164