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". */ 33 struct 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 44 struct vring_avail { 45 __u16 flags; 46 __u16 idx; 47 __u16 ring[]; 48 }; 49 50 /* u32 is used here for ids for padding reasons. */ 51 struct 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 58 struct vring_used { 59 __u16 flags; 60 __u16 idx; 61 struct vring_used_elem ring[]; 62 }; 63 64 struct 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 */ 96 static __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 } 105 106 static __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
