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 /* 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 {
  35         /* Address (guest-physical). */
  36         __u64 addr;
  37         /* Length. */
  38         __u32 len;
  39         /* The flags as indicated above. */
  40         __u16 flags;
  41         /* We chain unused descriptors via this, too */
  42         __u16 next;
  43 };
  44
  45 struct vring_avail
  46 {
  47         __u16 flags;
  48         __u16 idx;
  49         __u16 ring[];
  50 };
  51
  52 /* u32 is used here for ids for padding reasons. */
  53 struct vring_used_elem
  54 {
  55         /* Index of start of used descriptor chain. */
  56         __u32 id;
  57         /* Total length of the descriptor chain which was used (written to) */
  58         __u32 len;
  59 };
  60
  61 struct vring_used
  62 {
  63         __u16 flags;
  64         __u16 idx;
  65         struct vring_used_elem ring[];
  66 };
  67
  68 struct vring {
  69         unsigned int num;
  70
  71         struct vring_desc *desc;
  72
  73         struct vring_avail *avail;
  74
  75         struct vring_used *used;
  76 };
  77
  78 /* The standard layout for the ring is a continuous chunk of memory which looks
  79  * like this.  We assume num is a power of 2.
  80  *
  81  * struct vring
  82  * {
  83  *      // The actual descriptors (16 bytes each)
  84  *      struct vring_desc desc[num];
  85  *
  86  *      // A ring of available descriptor heads with free-running index.
  87  *      __u16 avail_flags;
  88  *      __u16 avail_idx;
  89  *      __u16 available[num];
  90  *
  91  *      // Padding to the next align boundary.
  92  *      char pad[];
  93  *
  94  *      // A ring of used descriptor heads with free-running index.
  95  *      __u16 used_flags;
  96  *      __u16 used_idx;
  97  *      struct vring_used_elem used[num];
  98  * };
  99  */
 100 static inline void vring_init(struct vring *vr, unsigned int num, void *p,
 101                               unsigned long align)
 102 {
 103         vr->num = num;
 104         vr->desc = p;
 105         vr->avail = p + num*sizeof(struct vring_desc);
 106         vr->used = (void *)(((unsigned long)&vr->avail->ring[num] + align-1)
 107                             & ~(align - 1));
 108 }
 109
 110 static inline unsigned vring_size(unsigned int num, unsigned long align)
 111 {
 112         return ((sizeof(struct vring_desc) * num + sizeof(__u16) * (2 + num)
 113                  + align - 1) & ~(align - 1))
 114                 + sizeof(__u16) * 2 + sizeof(struct vring_used_elem) * num;
 115 }
 116
 117 #ifdef __KERNEL__
 118 #include <linux/irqreturn.h>
 119 struct virtio_device;
 120 struct virtqueue;
 121
 122 struct virtqueue *vring_new_virtqueue(unsigned int num,
 123                                       unsigned int vring_align,
 124                                       struct virtio_device *vdev,
 125                                       void *pages,
 126                                       void (*notify)(struct virtqueue *vq),
 127                                       void (*callback)(struct virtqueue *vq),
 128                                       const char *name);
 129 void vring_del_virtqueue(struct virtqueue *vq);
 130 /* Filter out transport-specific feature bits. */
 131 void vring_transport_features(struct virtio_device *vdev);
 132
 133 irqreturn_t vring_interrupt(int irq, void *_vq);
 134 #endif /* __KERNEL__ */
 135 #endif /* _LINUX_VIRTIO_RING_H */