1 #ifndef _LINUX_VIRTIO_RING_H 2 #define _LINUX_VIRTIO_RING_H 3 /* An interface for efficient virtio implementation, currently for use by KVM, 4 * 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 #include "standard-headers/linux/types.h" 36 #include "standard-headers/linux/virtio_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 when 46 * you add a buffer. It's unreliable, so it's simply an optimization. Guest 47 * 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 interrupt me 50 * when you consume a buffer. It's unreliable, so it's simply an 51 * optimization. */ 52 #define VRING_AVAIL_F_NO_INTERRUPT 1 53 54 /* We support indirect buffer descriptors */ 55 #define VIRTIO_RING_F_INDIRECT_DESC 28 56 57 /* The Guest publishes the used index for which it expects an interrupt 58 * at the end of the avail ring. Host should ignore the avail->flags field. */ 59 /* The Host publishes the avail index for which it expects a kick 60 * at the end of the used ring. Guest should ignore the used->flags field. */ 61 #define VIRTIO_RING_F_EVENT_IDX 29 62 63 /* Virtio ring descriptors: 16 bytes. These can chain together via "next". */ 64 struct vring_desc { 65 /* Address (guest-physical). */ 66 __virtio64 addr; 67 /* Length. */ 68 __virtio32 len; 69 /* The flags as indicated above. */ 70 __virtio16 flags; 71 /* We chain unused descriptors via this, too */ 72 __virtio16 next; 73 }; 74 75 struct vring_avail { 76 __virtio16 flags; 77 __virtio16 idx; 78 __virtio16 ring[]; 79 }; 80 81 /* uint32_t is used here for ids for padding reasons. */ 82 struct vring_used_elem { 83 /* Index of start of used descriptor chain. */ 84 __virtio32 id; 85 /* Total length of the descriptor chain which was used (written to) */ 86 __virtio32 len; 87 }; 88 89 struct vring_used { 90 __virtio16 flags; 91 __virtio16 idx; 92 struct vring_used_elem ring[]; 93 }; 94 95 struct vring { 96 unsigned int num; 97 98 struct vring_desc *desc; 99 100 struct vring_avail *avail; 101 102 struct vring_used *used; 103 }; 104 105 /* Alignment requirements for vring elements. 106 * When using pre-virtio 1.0 layout, these fall out naturally. 107 */ 108 #define VRING_AVAIL_ALIGN_SIZE 2 109 #define VRING_USED_ALIGN_SIZE 4 110 #define VRING_DESC_ALIGN_SIZE 16 111 112 /* The standard layout for the ring is a continuous chunk of memory which looks 113 * like this. We assume num is a power of 2. 114 * 115 * struct vring 116 * { 117 * // The actual descriptors (16 bytes each) 118 * struct vring_desc desc[num]; 119 * 120 * // A ring of available descriptor heads with free-running index. 121 * __virtio16 avail_flags; 122 * __virtio16 avail_idx; 123 * __virtio16 available[num]; 124 * __virtio16 used_event_idx; 125 * 126 * // Padding to the next align boundary. 127 * char pad[]; 128 * 129 * // A ring of used descriptor heads with free-running index. 130 * __virtio16 used_flags; 131 * __virtio16 used_idx; 132 * struct vring_used_elem used[num]; 133 * __virtio16 avail_event_idx; 134 * }; 135 */ 136 /* We publish the used event index at the end of the available ring, and vice 137 * versa. They are at the end for backwards compatibility. */ 138 #define vring_used_event(vr) ((vr)->avail->ring[(vr)->num]) 139 #define vring_avail_event(vr) (*(__virtio16 *)&(vr)->used->ring[(vr)->num]) 140 141 static inline void vring_init(struct vring *vr, unsigned int num, void *p, 142 unsigned long align) 143 { 144 vr->num = num; 145 vr->desc = p; 146 vr->avail = p + num*sizeof(struct vring_desc); 147 vr->used = (void *)(((uintptr_t)&vr->avail->ring[num] + sizeof(__virtio16) 148 + align-1) & ~(align - 1)); 149 } 150 151 static inline unsigned vring_size(unsigned int num, unsigned long align) 152 { 153 return ((sizeof(struct vring_desc) * num + sizeof(__virtio16) * (3 + num) 154 + align - 1) & ~(align - 1)) 155 + sizeof(__virtio16) * 3 + sizeof(struct vring_used_elem) * num; 156 } 157 158 /* The following is used with USED_EVENT_IDX and AVAIL_EVENT_IDX */ 159 /* Assuming a given event_idx value from the other side, if 160 * we have just incremented index from old to new_idx, 161 * should we trigger an event? */ 162 static inline int vring_need_event(uint16_t event_idx, uint16_t new_idx, uint16_t old) 163 { 164 /* Note: Xen has similar logic for notification hold-off 165 * in include/xen/interface/io/ring.h with req_event and req_prod 166 * corresponding to event_idx + 1 and new_idx respectively. 167 * Note also that req_event and req_prod in Xen start at 1, 168 * event indexes in virtio start at 0. */ 169 return (uint16_t)(new_idx - event_idx - 1) < (uint16_t)(new_idx - old); 170 } 171 172 #endif /* _LINUX_VIRTIO_RING_H */ 173