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 * Copyright Rusty Russell IBM Corporation 2007. */ 11#include <linux/types.h> 12 13/* This marks a buffer as continuing via the next field. */ 14#define VRING_DESC_F_NEXT 1 15/* This marks a buffer as write-only (otherwise read-only). */ 16#define VRING_DESC_F_WRITE 2 17/* This means the buffer contains a list of buffer descriptors. */ 18#define VRING_DESC_F_INDIRECT 4 19 20/* The Host uses this in used->flags to advise the Guest: don't kick me when 21 * you add a buffer. It's unreliable, so it's simply an optimization. Guest 22 * will still kick if it's out of buffers. */ 23#define VRING_USED_F_NO_NOTIFY 1 24/* The Guest uses this in avail->flags to advise the Host: don't interrupt me 25 * when you consume a buffer. It's unreliable, so it's simply an 26 * optimization. */ 27#define VRING_AVAIL_F_NO_INTERRUPT 1 28 29/* We support indirect buffer descriptors */ 30#define VIRTIO_RING_F_INDIRECT_DESC 28 31 32/* Virtio ring descriptors: 16 bytes. These can chain together via "next". */ 33struct vring_desc { 34 /* Address (guest-physical). */ 35 __u64 addr; 36 /* Length. */ 37 __u32 len; 38 /* The flags as indicated above. */ 39 __u16 flags; 40 /* We chain unused descriptors via this, too */ 41 __u16 next; 42}; 43 44struct vring_avail { 45 __u16 flags; 46 __u16 idx; 47 __u16 ring[]; 48}; 49 50/* u32 is used here for ids for padding reasons. */ 51struct vring_used_elem { 52 /* Index of start of used descriptor chain. */ 53 __u32 id; 54 /* Total length of the descriptor chain which was used (written to) */ 55 __u32 len; 56}; 57 58struct vring_used { 59 __u16 flags; 60 __u16 idx; 61 struct vring_used_elem ring[]; 62}; 63 64struct vring { 65 unsigned int num; 66 67 struct vring_desc *desc; 68 69 struct vring_avail *avail; 70 71 struct vring_used *used; 72}; 73 74/* The standard layout for the ring is a continuous chunk of memory which looks 75 * like this. We assume num is a power of 2. 76 * 77 * struct vring 78 * { 79 * // The actual descriptors (16 bytes each) 80 * struct vring_desc desc[num]; 81 * 82 * // A ring of available descriptor heads with free-running index. 83 * __u16 avail_flags; 84 * __u16 avail_idx; 85 * __u16 available[num]; 86 * 87 * // Padding to the next align boundary. 88 * char pad[]; 89 * 90 * // A ring of used descriptor heads with free-running index. 91 * __u16 used_flags; 92 * __u16 used_idx; 93 * struct vring_used_elem used[num]; 94 * }; 95 */ 96static __inline__ void vring_init(struct vring *vr, unsigned int num, void *p, 97 unsigned long align) 98{ 99 vr->num = num; 100 vr->desc = p; 101 vr->avail = p + num*sizeof(struct vring_desc); 102 vr->used = (void *)(((unsigned long)&vr->avail->ring[num] + align-1) 103 & ~(align - 1)); 104} 105 106static __inline__ unsigned vring_size(unsigned int num, unsigned long align) 107{ 108 return ((sizeof(struct vring_desc) * num + sizeof(__u16) * (2 + num) 109 + align - 1) & ~(align - 1)) 110 + sizeof(__u16) * 2 + sizeof(struct vring_used_elem) * num; 111} 112 113#endif /* _LINUX_VIRTIO_RING_H */ 114