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 * 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 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". */ 62 struct vring_desc { 63 /* Address (guest-physical). */ 64 __u64 addr; 65 /* Length. */ 66 __u32 len; 67 /* The flags as indicated above. */ 68 __u16 flags; 69 /* We chain unused descriptors via this, too */ 70 __u16 next; 71 }; 72 73 struct vring_avail { 74 __u16 flags; 75 __u16 idx; 76 __u16 ring[]; 77 }; 78 79 /* u32 is used here for ids for padding reasons. */ 80 struct vring_used_elem { 81 /* Index of start of used descriptor chain. */ 82 __u32 id; 83 /* Total length of the descriptor chain which was used (written to) */ 84 __u32 len; 85 }; 86 87 struct vring_used { 88 __u16 flags; 89 __u16 idx; 90 struct vring_used_elem ring[]; 91 }; 92 93 struct 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 * __u16 avail_flags; 113 * __u16 avail_idx; 114 * __u16 available[num]; 115 * __u16 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 * __u16 used_flags; 122 * __u16 used_idx; 123 * struct vring_used_elem used[num]; 124 * __u16 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) (*(__u16 *)&(vr)->used->ring[(vr)->num]) 131 132 static __inline__ void vring_init(struct vring *vr, unsigned int num, void *p, 133 unsigned long align) 134 { 135 vr->num = num; 136 vr->desc = p; 137 vr->avail = p + num*sizeof(struct vring_desc); 138 vr->used = (void *)(((unsigned long)&vr->avail->ring[num] + sizeof(__u16) 139 + align-1) & ~(align - 1)); 140 } 141 142 static __inline__ unsigned vring_size(unsigned int num, unsigned long align) 143 { 144 return ((sizeof(struct vring_desc) * num + sizeof(__u16) * (3 + num) 145 + align - 1) & ~(align - 1)) 146 + sizeof(__u16) * 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? */ 153 static __inline__ int vring_need_event(__u16 event_idx, __u16 new_idx, __u16 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 (__u16)(new_idx - event_idx - 1) < (__u16)(new_idx - old); 161 } 162 163 #endif /* _LINUX_VIRTIO_RING_H */ 164
