1 /* 2 * This header is BSD licensed so anyone can use the definitions 3 * to implement compatible drivers/servers. 4 * 5 * Copyright Rusty Russell IBM Corporation 2007. 6 */ 7 /* $FreeBSD$ */ 8 9 #ifndef VIRTIO_RING_H 10 #define VIRTIO_RING_H 11 12 #include <sys/types.h> 13 14 /* This marks a buffer as continuing via the next field. */ 15 #define VRING_DESC_F_NEXT 1 16 /* This marks a buffer as write-only (otherwise read-only). */ 17 #define VRING_DESC_F_WRITE 2 18 /* This means the buffer contains a list of buffer descriptors. */ 19 #define VRING_DESC_F_INDIRECT 4 20 21 /* The Host uses this in used->flags to advise the Guest: don't kick me 22 * when you add a buffer. It's unreliable, so it's simply an 23 * optimization. Guest will still kick if it's out of buffers. */ 24 #define VRING_USED_F_NO_NOTIFY 1 25 /* The Guest uses this in avail->flags to advise the Host: don't 26 * interrupt me when you consume a buffer. It's unreliable, so it's 27 * simply an optimization. */ 28 #define VRING_AVAIL_F_NO_INTERRUPT 1 29 30 /* VirtIO ring descriptors: 16 bytes. 31 * These can chain together via "next". */ 32 struct vring_desc { 33 /* Address (guest-physical). */ 34 uint64_t addr; 35 /* Length. */ 36 uint32_t len; 37 /* The flags as indicated above. */ 38 uint16_t flags; 39 /* We chain unused descriptors via this, too. */ 40 uint16_t next; 41 }; 42 43 struct vring_avail { 44 uint16_t flags; 45 uint16_t idx; 46 uint16_t ring[0]; 47 }; 48 49 /* uint32_t is used here for ids for padding reasons. */ 50 struct vring_used_elem { 51 /* Index of start of used descriptor chain. */ 52 uint32_t id; 53 /* Total length of the descriptor chain which was written to. */ 54 uint32_t len; 55 }; 56 57 struct vring_used { 58 uint16_t flags; 59 uint16_t idx; 60 struct vring_used_elem ring[0]; 61 }; 62 63 struct vring { 64 unsigned int num; 65 66 struct vring_desc *desc; 67 struct vring_avail *avail; 68 struct vring_used *used; 69 }; 70 71 /* The standard layout for the ring is a continuous chunk of memory which 72 * looks like this. We assume num is a power of 2. 73 * 74 * struct vring { 75 * // The actual descriptors (16 bytes each) 76 * struct vring_desc desc[num]; 77 * 78 * // A ring of available descriptor heads with free-running index. 79 * __u16 avail_flags; 80 * __u16 avail_idx; 81 * __u16 available[num]; 82 * 83 * // Padding to the next align boundary. 84 * char pad[]; 85 * 86 * // A ring of used descriptor heads with free-running index. 87 * __u16 used_flags; 88 * __u16 used_idx; 89 * struct vring_used_elem used[num]; 90 * }; 91 * 92 * NOTE: for VirtIO PCI, align is 4096. 93 */ 94 95 static inline int 96 vring_size(unsigned int num, unsigned long align) 97 { 98 int size; 99 100 size = num * sizeof(struct vring_desc); 101 size += sizeof(struct vring_avail) + (num * sizeof(uint16_t)); 102 size = (size + align - 1) & ~(align - 1); 103 size += sizeof(struct vring_used) + 104 (num * sizeof(struct vring_used_elem)); 105 return (size); 106 } 107 108 static inline void 109 vring_init(struct vring *vr, unsigned int num, uint8_t *p, 110 unsigned long align) 111 { 112 vr->num = num; 113 vr->desc = (struct vring_desc *) p; 114 vr->avail = (struct vring_avail *) (p + 115 num * sizeof(struct vring_desc)); 116 vr->used = (void *) 117 (((unsigned long) &vr->avail->ring[num] + align-1) & ~(align-1)); 118 } 119 #endif /* VIRTIO_RING_H */ 120