include/linux/virtio_ring.h

   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
  18 /* The Host uses this in used->flags to advise the Guest: don't kick me when
  19  * you add a buffer.  It's unreliable, so it's simply an optimization.  Guest
  20  * will still kick if it's out of buffers. */
  21 #define VRING_USED_F_NO_NOTIFY  1
  22 /* The Guest uses this in avail->flags to advise the Host: don't interrupt me
  23  * when you consume a buffer.  It's unreliable, so it's simply an
  24  * optimization.  */
  25 #define VRING_AVAIL_F_NO_INTERRUPT      1
  26
  27 /* Virtio ring descriptors: 16 bytes.  These can chain together via "next". */
  28 struct vring_desc
  29 {
  30         /* Address (guest-physical). */
  31         __u64 addr;
  32         /* Length. */
  33         __u32 len;
  34         /* The flags as indicated above. */
  35         __u16 flags;
  36         /* We chain unused descriptors via this, too */
  37         __u16 next;
  38 };
  39
  40 struct vring_avail
  41 {
  42         __u16 flags;
  43         __u16 idx;
  44         __u16 ring[];
  45 };
  46
  47 /* u32 is used here for ids for padding reasons. */
  48 struct vring_used_elem
  49 {
  50         /* Index of start of used descriptor chain. */
  51         __u32 id;
  52         /* Total length of the descriptor chain which was used (written to) */
  53         __u32 len;
  54 };
  55
  56 struct vring_used
  57 {
  58         __u16 flags;
  59         __u16 idx;
  60         struct vring_used_elem ring[];
  61 };
  62
  63 struct vring {
  64         unsigned int num;
  65
  66         struct vring_desc *desc;
  67
  68         struct vring_avail *avail;
  69
  70         struct vring_used *used;
  71 };
  72
  73 /* The standard layout for the ring is a continuous chunk of memory which looks
  74  * like this.  We assume num is a power of 2.
  75  *
  76  * struct vring
  77  * {
  78  *      // The actual descriptors (16 bytes each)
  79  *      struct vring_desc desc[num];
  80  *
  81  *      // A ring of available descriptor heads with free-running index.
  82  *      __u16 avail_flags;
  83  *      __u16 avail_idx;
  84  *      __u16 available[num];
  85  *
  86  *      // Padding to the next page boundary.
  87  *      char pad[];
  88  *
  89  *      // A ring of used descriptor heads with free-running index.
  90  *      __u16 used_flags;
  91  *      __u16 used_idx;
  92  *      struct vring_used_elem used[num];
  93  * };
  94  */
  95 static inline void vring_init(struct vring *vr, unsigned int num, void *p,
  96                               unsigned long pagesize)
  97 {
  98         vr->num = num;
  99         vr->desc = p;
 100         vr->avail = p + num*sizeof(struct vring_desc);
 101         vr->used = (void *)(((unsigned long)&vr->avail->ring[num] + pagesize-1)
 102                             & ~(pagesize - 1));
 103 }
 104
 105 static inline unsigned vring_size(unsigned int num, unsigned long pagesize)
 106 {
 107         return ((sizeof(struct vring_desc) * num + sizeof(__u16) * (2 + num)
 108                  + pagesize - 1) & ~(pagesize - 1))
 109                 + sizeof(__u16) * 2 + sizeof(struct vring_used_elem) * num;
 110 }
 111
 112 #ifdef __KERNEL__
 113 #include <linux/irqreturn.h>
 114 struct virtio_device;
 115 struct virtqueue;
 116
 117 struct virtqueue *vring_new_virtqueue(unsigned int num,
 118                                       struct virtio_device *vdev,
 119                                       void *pages,
 120                                       void (*notify)(struct virtqueue *vq),
 121                                       void (*callback)(struct virtqueue *vq));
 122 void vring_del_virtqueue(struct virtqueue *vq);
 123 /* Filter out transport-specific feature bits. */
 124 void vring_transport_features(struct virtio_device *vdev);
 125
 126 irqreturn_t vring_interrupt(int irq, void *_vq);
 127 #endif /* __KERNEL__ */
 128 #endif /* _LINUX_VIRTIO_RING_H */