1 #ifndef _UAPI_LINUX_VIRTIO_RING_H 2 #define _UAPI_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 #ifndef __KERNEL__ 35 #include <stdint.h> 36 #endif 37 #include <linux/types.h> 38 #include <linux/virtio_types.h> 39 40 /* This marks a buffer as continuing via the next field. */ 41 #define VRING_DESC_F_NEXT 1 42 /* This marks a buffer as write-only (otherwise read-only). */ 43 #define VRING_DESC_F_WRITE 2 44 /* This means the buffer contains a list of buffer descriptors. */ 45 #define VRING_DESC_F_INDIRECT 4 46 47 /* The Host uses this in used->flags to advise the Guest: don't kick me when 48 * you add a buffer. It's unreliable, so it's simply an optimization. Guest 49 * will still kick if it's out of buffers. */ 50 #define VRING_USED_F_NO_NOTIFY 1 51 /* The Guest uses this in avail->flags to advise the Host: don't interrupt me 52 * when you consume a buffer. It's unreliable, so it's simply an 53 * optimization. */ 54 #define VRING_AVAIL_F_NO_INTERRUPT 1 55 56 /* We support indirect buffer descriptors */ 57 #define VIRTIO_RING_F_INDIRECT_DESC 28 58 59 /* The Guest publishes the used index for which it expects an interrupt 60 * at the end of the avail ring. Host should ignore the avail->flags field. */ 61 /* The Host publishes the avail index for which it expects a kick 62 * at the end of the used ring. Guest should ignore the used->flags field. */ 63 #define VIRTIO_RING_F_EVENT_IDX 29 64 65 /* Virtio ring descriptors: 16 bytes. These can chain together via "next". */ 66 struct vring_desc { 67 /* Address (guest-physical). */ 68 __virtio64 addr; 69 /* Length. */ 70 __virtio32 len; 71 /* The flags as indicated above. */ 72 __virtio16 flags; 73 /* We chain unused descriptors via this, too */ 74 __virtio16 next; 75 }; 76 77 struct vring_avail { 78 __virtio16 flags; 79 __virtio16 idx; 80 __virtio16 ring[]; 81 }; 82 83 /* u32 is used here for ids for padding reasons. */ 84 struct vring_used_elem { 85 /* Index of start of used descriptor chain. */ 86 __virtio32 id; 87 /* Total length of the descriptor chain which was used (written to) */ 88 __virtio32 len; 89 }; 90 91 struct vring_used { 92 __virtio16 flags; 93 __virtio16 idx; 94 struct vring_used_elem ring[]; 95 }; 96 97 struct vring { 98 unsigned int num; 99 100 struct vring_desc *desc; 101 102 struct vring_avail *avail; 103 104 struct vring_used *used; 105 }; 106 107 /* Alignment requirements for vring elements. 108 * When using pre-virtio 1.0 layout, these fall out naturally. 109 */ 110 #define VRING_AVAIL_ALIGN_SIZE 2 111 #define VRING_USED_ALIGN_SIZE 4 112 #define VRING_DESC_ALIGN_SIZE 16 113 114 /* The standard layout for the ring is a continuous chunk of memory which looks 115 * like this. We assume num is a power of 2. 116 * 117 * struct vring 118 * { 119 * // The actual descriptors (16 bytes each) 120 * struct vring_desc desc[num]; 121 * 122 * // A ring of available descriptor heads with free-running index. 123 * __virtio16 avail_flags; 124 * __virtio16 avail_idx; 125 * __virtio16 available[num]; 126 * __virtio16 used_event_idx; 127 * 128 * // Padding to the next align boundary. 129 * char pad[]; 130 * 131 * // A ring of used descriptor heads with free-running index. 132 * __virtio16 used_flags; 133 * __virtio16 used_idx; 134 * struct vring_used_elem used[num]; 135 * __virtio16 avail_event_idx; 136 * }; 137 */ 138 /* We publish the used event index at the end of the available ring, and vice 139 * versa. They are at the end for backwards compatibility. */ 140 #define vring_used_event(vr) ((vr)->avail->ring[(vr)->num]) 141 #define vring_avail_event(vr) (*(__virtio16 *)&(vr)->used->ring[(vr)->num]) 142 143 static inline void vring_init(struct vring *vr, unsigned int num, void *p, 144 unsigned long align) 145 { 146 vr->num = num; 147 vr->desc = p; 148 vr->avail = p + num*sizeof(struct vring_desc); 149 vr->used = (void *)(((uintptr_t)&vr->avail->ring[num] + sizeof(__virtio16) 150 + align-1) & ~(align - 1)); 151 } 152 153 static inline unsigned vring_size(unsigned int num, unsigned long align) 154 { 155 return ((sizeof(struct vring_desc) * num + sizeof(__virtio16) * (3 + num) 156 + align - 1) & ~(align - 1)) 157 + sizeof(__virtio16) * 3 + sizeof(struct vring_used_elem) * num; 158 } 159 160 /* The following is used with USED_EVENT_IDX and AVAIL_EVENT_IDX */ 161 /* Assuming a given event_idx value from the other side, if 162 * we have just incremented index from old to new_idx, 163 * should we trigger an event? */ 164 static inline int vring_need_event(__u16 event_idx, __u16 new_idx, __u16 old) 165 { 166 /* Note: Xen has similar logic for notification hold-off 167 * in include/xen/interface/io/ring.h with req_event and req_prod 168 * corresponding to event_idx + 1 and new_idx respectively. 169 * Note also that req_event and req_prod in Xen start at 1, 170 * event indexes in virtio start at 0. */ 171 return (__u16)(new_idx - event_idx - 1) < (__u16)(new_idx - old); 172 } 173 174 #endif /* _UAPI_LINUX_VIRTIO_RING_H */ 175