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