/*
   * Helpers for the host side of a virtio ring.
   *
   * Since these may be in userspace, we use (inline) accessors.
   */

  #include <linux/module.h>

  #include <linux/vringh.h>
  #include <linux/virtio_ring.h>
  #include <linux/kernel.h>
  #include <linux/ratelimit.h>
  #include <linux/uaccess.h>
  #include <linux/slab.h>
  #include <linux/export.h>

  #include <uapi/linux/virtio_config.h>

  
  static __printf(1,2) __cold void vringh_bad(const char *fmt, ...)
  {
  	static DEFINE_RATELIMIT_STATE(vringh_rs,
  				      DEFAULT_RATELIMIT_INTERVAL,
  				      DEFAULT_RATELIMIT_BURST);
  	if (__ratelimit(&vringh_rs)) {
  		va_list ap;
  		va_start(ap, fmt);
  		printk(KERN_NOTICE "vringh:");
  		vprintk(fmt, ap);
  		va_end(ap);
  	}
  }
  
  /* Returns vring->num if empty, -ve on error. */
  static inline int __vringh_get_head(const struct vringh *vrh,

  				    int (*getu16)(const struct vringh *vrh,
  						  u16 *val, const __virtio16 *p),

  				    u16 *last_avail_idx)
  {
  	u16 avail_idx, i, head;
  	int err;

  	err = getu16(vrh, &avail_idx, &vrh->vring.avail->idx);

  	if (err) {
  		vringh_bad("Failed to access avail idx at %p",
  			   &vrh->vring.avail->idx);
  		return err;
  	}
  
  	if (*last_avail_idx == avail_idx)
  		return vrh->vring.num;
  
  	/* Only get avail ring entries after they have been exposed by guest. */
  	virtio_rmb(vrh->weak_barriers);
  
  	i = *last_avail_idx & (vrh->vring.num - 1);

  	err = getu16(vrh, &head, &vrh->vring.avail->ring[i]);

  	if (err) {
  		vringh_bad("Failed to read head: idx %d address %p",
  			   *last_avail_idx, &vrh->vring.avail->ring[i]);
  		return err;
  	}
  
  	if (head >= vrh->vring.num) {
  		vringh_bad("Guest says index %u > %u is available",
  			   head, vrh->vring.num);
  		return -EINVAL;
  	}
  
  	(*last_avail_idx)++;
  	return head;
  }
  
  /* Copy some bytes to/from the iovec.  Returns num copied. */
  static inline ssize_t vringh_iov_xfer(struct vringh_kiov *iov,
  				      void *ptr, size_t len,
  				      int (*xfer)(void *addr, void *ptr,
  						  size_t len))
  {
  	int err, done = 0;
  
  	while (len && iov->i < iov->used) {
  		size_t partlen;
  
  		partlen = min(iov->iov[iov->i].iov_len, len);
  		err = xfer(iov->iov[iov->i].iov_base, ptr, partlen);
  		if (err)
  			return err;
  		done += partlen;
  		len -= partlen;
  		ptr += partlen;
  		iov->consumed += partlen;
  		iov->iov[iov->i].iov_len -= partlen;
  		iov->iov[iov->i].iov_base += partlen;
  
  		if (!iov->iov[iov->i].iov_len) {
  			/* Fix up old iov element then increment. */
  			iov->iov[iov->i].iov_len = iov->consumed;
  			iov->iov[iov->i].iov_base -= iov->consumed;
  			
  			iov->consumed = 0;
  			iov->i++;
  		}
  	}
  	return done;
  }
  
  /* May reduce *len if range is shorter. */
  static inline bool range_check(struct vringh *vrh, u64 addr, size_t *len,
  			       struct vringh_range *range,
  			       bool (*getrange)(struct vringh *,
  						u64, struct vringh_range *))
  {
  	if (addr < range->start || addr > range->end_incl) {
  		if (!getrange(vrh, addr, range))
  			return false;
  	}
  	BUG_ON(addr < range->start || addr > range->end_incl);
  
  	/* To end of memory? */
  	if (unlikely(addr + *len == 0)) {
  		if (range->end_incl == -1ULL)
  			return true;
  		goto truncate;
  	}
  
  	/* Otherwise, don't wrap. */
  	if (addr + *len < addr) {
  		vringh_bad("Wrapping descriptor %zu@0x%llx",
  			   *len, (unsigned long long)addr);
  		return false;
  	}
  
  	if (unlikely(addr + *len - 1 > range->end_incl))
  		goto truncate;
  	return true;
  
  truncate:
  	*len = range->end_incl + 1 - addr;
  	return true;
  }
  
  static inline bool no_range_check(struct vringh *vrh, u64 addr, size_t *len,
  				  struct vringh_range *range,
  				  bool (*getrange)(struct vringh *,
  						   u64, struct vringh_range *))
  {
  	return true;
  }
  
  /* No reason for this code to be inline. */

  static int move_to_indirect(const struct vringh *vrh,
  			    int *up_next, u16 *i, void *addr,

  			    const struct vring_desc *desc,
  			    struct vring_desc **descs, int *desc_max)
  {

  	u32 len;

  	/* Indirect tables can't have indirect. */
  	if (*up_next != -1) {
  		vringh_bad("Multilevel indirect %u->%u", *up_next, *i);
  		return -EINVAL;
  	}

  	len = vringh32_to_cpu(vrh, desc->len);
  	if (unlikely(len % sizeof(struct vring_desc))) {

  		vringh_bad("Strange indirect len %u", desc->len);
  		return -EINVAL;
  	}
  
  	/* We will check this when we follow it! */

  	if (desc->flags & cpu_to_vringh16(vrh, VRING_DESC_F_NEXT))
  		*up_next = vringh16_to_cpu(vrh, desc->next);

  	else
  		*up_next = -2;
  	*descs = addr;

  	*desc_max = len / sizeof(struct vring_desc);

  
  	/* Now, start at the first indirect. */
  	*i = 0;
  	return 0;
  }
  
  static int resize_iovec(struct vringh_kiov *iov, gfp_t gfp)
  {
  	struct kvec *new;
  	unsigned int flag, new_num = (iov->max_num & ~VRINGH_IOV_ALLOCATED) * 2;
  
  	if (new_num < 8)
  		new_num = 8;
  
  	flag = (iov->max_num & VRINGH_IOV_ALLOCATED);
  	if (flag)
  		new = krealloc(iov->iov, new_num * sizeof(struct iovec), gfp);
  	else {
  		new = kmalloc(new_num * sizeof(struct iovec), gfp);
  		if (new) {
  			memcpy(new, iov->iov,
  			       iov->max_num * sizeof(struct iovec));
  			flag = VRINGH_IOV_ALLOCATED;
  		}
  	}
  	if (!new)
  		return -ENOMEM;
  	iov->iov = new;
  	iov->max_num = (new_num | flag);
  	return 0;
  }
  
  static u16 __cold return_from_indirect(const struct vringh *vrh, int *up_next,
  				       struct vring_desc **descs, int *desc_max)
  {
  	u16 i = *up_next;
  
  	*up_next = -1;
  	*descs = vrh->vring.desc;
  	*desc_max = vrh->vring.num;
  	return i;
  }
  
  static int slow_copy(struct vringh *vrh, void *dst, const void *src,
  		     bool (*rcheck)(struct vringh *vrh, u64 addr, size_t *len,
  				    struct vringh_range *range,
  				    bool (*getrange)(struct vringh *vrh,
  						     u64,
  						     struct vringh_range *)),
  		     bool (*getrange)(struct vringh *vrh,
  				      u64 addr,
  				      struct vringh_range *r),
  		     struct vringh_range *range,
  		     int (*copy)(void *dst, const void *src, size_t len))
  {
  	size_t part, len = sizeof(struct vring_desc);
  
  	do {
  		u64 addr;
  		int err;
  
  		part = len;
  		addr = (u64)(unsigned long)src - range->offset;
  
  		if (!rcheck(vrh, addr, &part, range, getrange))
  			return -EINVAL;
  
  		err = copy(dst, src, part);
  		if (err)
  			return err;
  
  		dst += part;
  		src += part;
  		len -= part;
  	} while (len);
  	return 0;
  }
  
  static inline int
  __vringh_iov(struct vringh *vrh, u16 i,
  	     struct vringh_kiov *riov,
  	     struct vringh_kiov *wiov,
  	     bool (*rcheck)(struct vringh *vrh, u64 addr, size_t *len,
  			    struct vringh_range *range,
  			    bool (*getrange)(struct vringh *, u64,
  					     struct vringh_range *)),
  	     bool (*getrange)(struct vringh *, u64, struct vringh_range *),
  	     gfp_t gfp,
  	     int (*copy)(void *dst, const void *src, size_t len))
  {
  	int err, count = 0, up_next, desc_max;
  	struct vring_desc desc, *descs;
  	struct vringh_range range = { -1ULL, 0 }, slowrange;
  	bool slow = false;
  
  	/* We start traversing vring's descriptor table. */
  	descs = vrh->vring.desc;
  	desc_max = vrh->vring.num;
  	up_next = -1;
  
  	if (riov)
  		riov->i = riov->used = 0;
  	else if (wiov)
  		wiov->i = wiov->used = 0;
  	else
  		/* You must want something! */
  		BUG();
  
  	for (;;) {
  		void *addr;
  		struct vringh_kiov *iov;
  		size_t len;
  
  		if (unlikely(slow))
  			err = slow_copy(vrh, &desc, &descs[i], rcheck, getrange,
  					&slowrange, copy);
  		else
  			err = copy(&desc, &descs[i], sizeof(desc));
  		if (unlikely(err))
  			goto fail;

  		if (unlikely(desc.flags &
  			     cpu_to_vringh16(vrh, VRING_DESC_F_INDIRECT))) {
  			u64 a = vringh64_to_cpu(vrh, desc.addr);

  			/* Make sure it's OK, and get offset. */

  			len = vringh32_to_cpu(vrh, desc.len);
  			if (!rcheck(vrh, a, &len, &range, getrange)) {

  				err = -EINVAL;
  				goto fail;
  			}

  			if (unlikely(len != vringh32_to_cpu(vrh, desc.len))) {

  				slow = true;
  				/* We need to save this range to use offset */
  				slowrange = range;
  			}

  			addr = (void *)(long)(a + range.offset);
  			err = move_to_indirect(vrh, &up_next, &i, addr, &desc,

  					       &descs, &desc_max);
  			if (err)
  				goto fail;
  			continue;
  		}
  
  		if (count++ == vrh->vring.num) {
  			vringh_bad("Descriptor loop in %p", descs);
  			err = -ELOOP;
  			goto fail;
  		}

  		if (desc.flags & cpu_to_vringh16(vrh, VRING_DESC_F_WRITE))

  			iov = wiov;
  		else {
  			iov = riov;
  			if (unlikely(wiov && wiov->i)) {
  				vringh_bad("Readable desc %p after writable",
  					   &descs[i]);
  				err = -EINVAL;
  				goto fail;
  			}
  		}
  
  		if (!iov) {
  			vringh_bad("Unexpected %s desc",
  				   !wiov ? "writable" : "readable");
  			err = -EPROTO;
  			goto fail;
  		}
  
  	again:
  		/* Make sure it's OK, and get offset. */

  		len = vringh32_to_cpu(vrh, desc.len);
  		if (!rcheck(vrh, vringh64_to_cpu(vrh, desc.addr), &len, &range,
  			    getrange)) {

  			err = -EINVAL;
  			goto fail;
  		}

  		addr = (void *)(unsigned long)(vringh64_to_cpu(vrh, desc.addr) +
  					       range.offset);

  
  		if (unlikely(iov->used == (iov->max_num & ~VRINGH_IOV_ALLOCATED))) {
  			err = resize_iovec(iov, gfp);
  			if (err)
  				goto fail;
  		}
  
  		iov->iov[iov->used].iov_base = addr;
  		iov->iov[iov->used].iov_len = len;
  		iov->used++;

  		if (unlikely(len != vringh32_to_cpu(vrh, desc.len))) {
  			desc.len = cpu_to_vringh32(vrh,
  				   vringh32_to_cpu(vrh, desc.len) - len);
  			desc.addr = cpu_to_vringh64(vrh,
  				    vringh64_to_cpu(vrh, desc.addr) + len);

  			goto again;
  		}

  		if (desc.flags & cpu_to_vringh16(vrh, VRING_DESC_F_NEXT)) {
  			i = vringh16_to_cpu(vrh, desc.next);

  		} else {
  			/* Just in case we need to finish traversing above. */
  			if (unlikely(up_next > 0)) {
  				i = return_from_indirect(vrh, &up_next,
  							 &descs, &desc_max);
  				slow = false;
  			} else
  				break;
  		}
  
  		if (i >= desc_max) {
  			vringh_bad("Chained index %u > %u", i, desc_max);
  			err = -EINVAL;
  			goto fail;
  		}
  	}
  
  	return 0;
  
  fail:
  	return err;
  }
  
  static inline int __vringh_complete(struct vringh *vrh,
  				    const struct vring_used_elem *used,
  				    unsigned int num_used,

  				    int (*putu16)(const struct vringh *vrh,
  						  __virtio16 *p, u16 val),

  				    int (*putused)(struct vring_used_elem *dst,
  						   const struct vring_used_elem
  						   *src, unsigned num))
  {
  	struct vring_used *used_ring;
  	int err;
  	u16 used_idx, off;
  
  	used_ring = vrh->vring.used;
  	used_idx = vrh->last_used_idx + vrh->completed;
  
  	off = used_idx % vrh->vring.num;
  
  	/* Compiler knows num_used == 1 sometimes, hence extra check */
  	if (num_used > 1 && unlikely(off + num_used >= vrh->vring.num)) {
  		u16 part = vrh->vring.num - off;
  		err = putused(&used_ring->ring[off], used, part);
  		if (!err)
  			err = putused(&used_ring->ring[0], used + part,
  				      num_used - part);
  	} else
  		err = putused(&used_ring->ring[off], used, num_used);
  
  	if (err) {
  		vringh_bad("Failed to write %u used entries %u at %p",
  			   num_used, off, &used_ring->ring[off]);
  		return err;
  	}
  
  	/* Make sure buffer is written before we update index. */
  	virtio_wmb(vrh->weak_barriers);

  	err = putu16(vrh, &vrh->vring.used->idx, used_idx + num_used);

  	if (err) {
  		vringh_bad("Failed to update used index at %p",
  			   &vrh->vring.used->idx);
  		return err;
  	}
  
  	vrh->completed += num_used;
  	return 0;
  }
  
  
  static inline int __vringh_need_notify(struct vringh *vrh,

  				       int (*getu16)(const struct vringh *vrh,
  						     u16 *val,
  						     const __virtio16 *p))

  {
  	bool notify;
  	u16 used_event;
  	int err;
  
  	/* Flush out used index update. This is paired with the
  	 * barrier that the Guest executes when enabling
  	 * interrupts. */
  	virtio_mb(vrh->weak_barriers);
  
  	/* Old-style, without event indices. */
  	if (!vrh->event_indices) {
  		u16 flags;

  		err = getu16(vrh, &flags, &vrh->vring.avail->flags);

  		if (err) {
  			vringh_bad("Failed to get flags at %p",
  				   &vrh->vring.avail->flags);
  			return err;
  		}
  		return (!(flags & VRING_AVAIL_F_NO_INTERRUPT));
  	}
  
  	/* Modern: we know when other side wants to know. */

  	err = getu16(vrh, &used_event, &vring_used_event(&vrh->vring));

  	if (err) {
  		vringh_bad("Failed to get used event idx at %p",
  			   &vring_used_event(&vrh->vring));
  		return err;
  	}
  
  	/* Just in case we added so many that we wrap. */
  	if (unlikely(vrh->completed > 0xffff))
  		notify = true;
  	else
  		notify = vring_need_event(used_event,
  					  vrh->last_used_idx + vrh->completed,
  					  vrh->last_used_idx);
  
  	vrh->last_used_idx += vrh->completed;
  	vrh->completed = 0;
  	return notify;
  }
  
  static inline bool __vringh_notify_enable(struct vringh *vrh,

  					  int (*getu16)(const struct vringh *vrh,
  							u16 *val, const __virtio16 *p),
  					  int (*putu16)(const struct vringh *vrh,
  							__virtio16 *p, u16 val))

  {
  	u16 avail;
  
  	if (!vrh->event_indices) {
  		/* Old-school; update flags. */

  		if (putu16(vrh, &vrh->vring.used->flags, 0) != 0) {

  			vringh_bad("Clearing used flags %p",
  				   &vrh->vring.used->flags);
  			return true;
  		}
  	} else {

  		if (putu16(vrh, &vring_avail_event(&vrh->vring),

  			   vrh->last_avail_idx) != 0) {
  			vringh_bad("Updating avail event index %p",
  				   &vring_avail_event(&vrh->vring));
  			return true;
  		}
  	}
  
  	/* They could have slipped one in as we were doing that: make
  	 * sure it's written, then check again. */
  	virtio_mb(vrh->weak_barriers);

  	if (getu16(vrh, &avail, &vrh->vring.avail->idx) != 0) {

  		vringh_bad("Failed to check avail idx at %p",
  			   &vrh->vring.avail->idx);
  		return true;
  	}
  
  	/* This is unlikely, so we just leave notifications enabled
  	 * (if we're using event_indices, we'll only get one
  	 * notification anyway). */
  	return avail == vrh->last_avail_idx;
  }
  
  static inline void __vringh_notify_disable(struct vringh *vrh,

  					   int (*putu16)(const struct vringh *vrh,
  							 __virtio16 *p, u16 val))

  {
  	if (!vrh->event_indices) {
  		/* Old-school; update flags. */

  		if (putu16(vrh, &vrh->vring.used->flags,
  			   VRING_USED_F_NO_NOTIFY)) {

  			vringh_bad("Setting used flags %p",
  				   &vrh->vring.used->flags);
  		}
  	}
  }
  
  /* Userspace access helpers: in this case, addresses are really userspace. */

  static inline int getu16_user(const struct vringh *vrh, u16 *val, const __virtio16 *p)

  {

  	__virtio16 v = 0;
  	int rc = get_user(v, (__force __virtio16 __user *)p);
  	*val = vringh16_to_cpu(vrh, v);
  	return rc;

  }

  static inline int putu16_user(const struct vringh *vrh, __virtio16 *p, u16 val)

  {

  	__virtio16 v = cpu_to_vringh16(vrh, val);
  	return put_user(v, (__force __virtio16 __user *)p);

  }
  
  static inline int copydesc_user(void *dst, const void *src, size_t len)
  {
  	return copy_from_user(dst, (__force void __user *)src, len) ?
  		-EFAULT : 0;
  }
  
  static inline int putused_user(struct vring_used_elem *dst,
  			       const struct vring_used_elem *src,
  			       unsigned int num)
  {
  	return copy_to_user((__force void __user *)dst, src,
  			    sizeof(*dst) * num) ? -EFAULT : 0;
  }
  
  static inline int xfer_from_user(void *src, void *dst, size_t len)
  {
  	return copy_from_user(dst, (__force void __user *)src, len) ?
  		-EFAULT : 0;
  }
  
  static inline int xfer_to_user(void *dst, void *src, size_t len)
  {
  	return copy_to_user((__force void __user *)dst, src, len) ?
  		-EFAULT : 0;
  }
  
  /**
   * vringh_init_user - initialize a vringh for a userspace vring.
   * @vrh: the vringh to initialize.
   * @features: the feature bits for this ring.
   * @num: the number of elements.
   * @weak_barriers: true if we only need memory barriers, not I/O.
   * @desc: the userpace descriptor pointer.
   * @avail: the userpace avail pointer.
   * @used: the userpace used pointer.
   *
   * Returns an error if num is invalid: you should check pointers
   * yourself!
   */

  int vringh_init_user(struct vringh *vrh, u64 features,

  		     unsigned int num, bool weak_barriers,
  		     struct vring_desc __user *desc,
  		     struct vring_avail __user *avail,
  		     struct vring_used __user *used)
  {
  	/* Sane power of 2 please! */
  	if (!num || num > 0xffff || (num & (num - 1))) {
  		vringh_bad("Bad ring size %u", num);
  		return -EINVAL;
  	}

  	vrh->little_endian = (features & (1ULL << VIRTIO_F_VERSION_1));

  	vrh->event_indices = (features & (1 << VIRTIO_RING_F_EVENT_IDX));
  	vrh->weak_barriers = weak_barriers;
  	vrh->completed = 0;
  	vrh->last_avail_idx = 0;
  	vrh->last_used_idx = 0;
  	vrh->vring.num = num;
  	/* vring expects kernel addresses, but only used via accessors. */
  	vrh->vring.desc = (__force struct vring_desc *)desc;
  	vrh->vring.avail = (__force struct vring_avail *)avail;
  	vrh->vring.used = (__force struct vring_used *)used;
  	return 0;
  }
  EXPORT_SYMBOL(vringh_init_user);
  
  /**
   * vringh_getdesc_user - get next available descriptor from userspace ring.
   * @vrh: the userspace vring.
   * @riov: where to put the readable descriptors (or NULL)
   * @wiov: where to put the writable descriptors (or NULL)
   * @getrange: function to call to check ranges.
   * @head: head index we received, for passing to vringh_complete_user().
   *
   * Returns 0 if there was no descriptor, 1 if there was, or -errno.
   *
   * Note that on error return, you can tell the difference between an
   * invalid ring and a single invalid descriptor: in the former case,
   * *head will be vrh->vring.num.  You may be able to ignore an invalid
   * descriptor, but there's not much you can do with an invalid ring.
   *
   * Note that you may need to clean up riov and wiov, even on error!
   */
  int vringh_getdesc_user(struct vringh *vrh,
  			struct vringh_iov *riov,
  			struct vringh_iov *wiov,
  			bool (*getrange)(struct vringh *vrh,
  					 u64 addr, struct vringh_range *r),
  			u16 *head)
  {
  	int err;
  
  	*head = vrh->vring.num;
  	err = __vringh_get_head(vrh, getu16_user, &vrh->last_avail_idx);
  	if (err < 0)
  		return err;
  
  	/* Empty... */
  	if (err == vrh->vring.num)
  		return 0;
  
  	/* We need the layouts to be the identical for this to work */
  	BUILD_BUG_ON(sizeof(struct vringh_kiov) != sizeof(struct vringh_iov));
  	BUILD_BUG_ON(offsetof(struct vringh_kiov, iov) !=
  		     offsetof(struct vringh_iov, iov));
  	BUILD_BUG_ON(offsetof(struct vringh_kiov, i) !=
  		     offsetof(struct vringh_iov, i));
  	BUILD_BUG_ON(offsetof(struct vringh_kiov, used) !=
  		     offsetof(struct vringh_iov, used));
  	BUILD_BUG_ON(offsetof(struct vringh_kiov, max_num) !=
  		     offsetof(struct vringh_iov, max_num));
  	BUILD_BUG_ON(sizeof(struct iovec) != sizeof(struct kvec));
  	BUILD_BUG_ON(offsetof(struct iovec, iov_base) !=
  		     offsetof(struct kvec, iov_base));
  	BUILD_BUG_ON(offsetof(struct iovec, iov_len) !=
  		     offsetof(struct kvec, iov_len));
  	BUILD_BUG_ON(sizeof(((struct iovec *)NULL)->iov_base)
  		     != sizeof(((struct kvec *)NULL)->iov_base));
  	BUILD_BUG_ON(sizeof(((struct iovec *)NULL)->iov_len)
  		     != sizeof(((struct kvec *)NULL)->iov_len));
  
  	*head = err;
  	err = __vringh_iov(vrh, *head, (struct vringh_kiov *)riov,
  			   (struct vringh_kiov *)wiov,
  			   range_check, getrange, GFP_KERNEL, copydesc_user);
  	if (err)
  		return err;
  
  	return 1;
  }
  EXPORT_SYMBOL(vringh_getdesc_user);
  
  /**
   * vringh_iov_pull_user - copy bytes from vring_iov.
   * @riov: the riov as passed to vringh_getdesc_user() (updated as we consume)
   * @dst: the place to copy.
   * @len: the maximum length to copy.
   *
   * Returns the bytes copied <= len or a negative errno.
   */
  ssize_t vringh_iov_pull_user(struct vringh_iov *riov, void *dst, size_t len)
  {
  	return vringh_iov_xfer((struct vringh_kiov *)riov,
  			       dst, len, xfer_from_user);
  }
  EXPORT_SYMBOL(vringh_iov_pull_user);
  
  /**
   * vringh_iov_push_user - copy bytes into vring_iov.
   * @wiov: the wiov as passed to vringh_getdesc_user() (updated as we consume)
   * @dst: the place to copy.
   * @len: the maximum length to copy.
   *
   * Returns the bytes copied <= len or a negative errno.
   */
  ssize_t vringh_iov_push_user(struct vringh_iov *wiov,
  			     const void *src, size_t len)
  {
  	return vringh_iov_xfer((struct vringh_kiov *)wiov,
  			       (void *)src, len, xfer_to_user);
  }
  EXPORT_SYMBOL(vringh_iov_push_user);
  
  /**
   * vringh_abandon_user - we've decided not to handle the descriptor(s).
   * @vrh: the vring.
   * @num: the number of descriptors to put back (ie. num
   *	 vringh_get_user() to undo).
   *
   * The next vringh_get_user() will return the old descriptor(s) again.
   */
  void vringh_abandon_user(struct vringh *vrh, unsigned int num)
  {
  	/* We only update vring_avail_event(vr) when we want to be notified,
  	 * so we haven't changed that yet. */
  	vrh->last_avail_idx -= num;
  }
  EXPORT_SYMBOL(vringh_abandon_user);
  
  /**
   * vringh_complete_user - we've finished with descriptor, publish it.
   * @vrh: the vring.
   * @head: the head as filled in by vringh_getdesc_user.
   * @len: the length of data we have written.
   *
   * You should check vringh_need_notify_user() after one or more calls
   * to this function.
   */
  int vringh_complete_user(struct vringh *vrh, u16 head, u32 len)
  {
  	struct vring_used_elem used;

  	used.id = cpu_to_vringh32(vrh, head);
  	used.len = cpu_to_vringh32(vrh, len);

  	return __vringh_complete(vrh, &used, 1, putu16_user, putused_user);
  }
  EXPORT_SYMBOL(vringh_complete_user);
  
  /**
   * vringh_complete_multi_user - we've finished with many descriptors.
   * @vrh: the vring.
   * @used: the head, length pairs.
   * @num_used: the number of used elements.
   *
   * You should check vringh_need_notify_user() after one or more calls
   * to this function.
   */
  int vringh_complete_multi_user(struct vringh *vrh,
  			       const struct vring_used_elem used[],
  			       unsigned num_used)
  {
  	return __vringh_complete(vrh, used, num_used,
  				 putu16_user, putused_user);
  }
  EXPORT_SYMBOL(vringh_complete_multi_user);
  
  /**
   * vringh_notify_enable_user - we want to know if something changes.
   * @vrh: the vring.
   *
   * This always enables notifications, but returns false if there are
   * now more buffers available in the vring.
   */
  bool vringh_notify_enable_user(struct vringh *vrh)
  {
  	return __vringh_notify_enable(vrh, getu16_user, putu16_user);
  }
  EXPORT_SYMBOL(vringh_notify_enable_user);
  
  /**
   * vringh_notify_disable_user - don't tell us if something changes.
   * @vrh: the vring.
   *
   * This is our normal running state: we disable and then only enable when
   * we're going to sleep.
   */
  void vringh_notify_disable_user(struct vringh *vrh)
  {
  	__vringh_notify_disable(vrh, putu16_user);
  }
  EXPORT_SYMBOL(vringh_notify_disable_user);
  
  /**
   * vringh_need_notify_user - must we tell the other side about used buffers?
   * @vrh: the vring we've called vringh_complete_user() on.
   *
   * Returns -errno or 0 if we don't need to tell the other side, 1 if we do.
   */
  int vringh_need_notify_user(struct vringh *vrh)
  {
  	return __vringh_need_notify(vrh, getu16_user);
  }
  EXPORT_SYMBOL(vringh_need_notify_user);
  
  /* Kernelspace access helpers. */

  static inline int getu16_kern(const struct vringh *vrh,
  			      u16 *val, const __virtio16 *p)

  {

  	*val = vringh16_to_cpu(vrh, ACCESS_ONCE(*p));

  	return 0;
  }

  static inline int putu16_kern(const struct vringh *vrh, __virtio16 *p, u16 val)

  {

  	ACCESS_ONCE(*p) = cpu_to_vringh16(vrh, val);

  	return 0;
  }
  
  static inline int copydesc_kern(void *dst, const void *src, size_t len)
  {
  	memcpy(dst, src, len);
  	return 0;
  }
  
  static inline int putused_kern(struct vring_used_elem *dst,
  			       const struct vring_used_elem *src,
  			       unsigned int num)
  {
  	memcpy(dst, src, num * sizeof(*dst));
  	return 0;
  }
  
  static inline int xfer_kern(void *src, void *dst, size_t len)
  {
  	memcpy(dst, src, len);
  	return 0;
  }
  
  /**
   * vringh_init_kern - initialize a vringh for a kernelspace vring.
   * @vrh: the vringh to initialize.
   * @features: the feature bits for this ring.
   * @num: the number of elements.
   * @weak_barriers: true if we only need memory barriers, not I/O.
   * @desc: the userpace descriptor pointer.
   * @avail: the userpace avail pointer.
   * @used: the userpace used pointer.
   *
   * Returns an error if num is invalid.
   */

  int vringh_init_kern(struct vringh *vrh, u64 features,

  		     unsigned int num, bool weak_barriers,
  		     struct vring_desc *desc,
  		     struct vring_avail *avail,
  		     struct vring_used *used)
  {
  	/* Sane power of 2 please! */
  	if (!num || num > 0xffff || (num & (num - 1))) {
  		vringh_bad("Bad ring size %u", num);
  		return -EINVAL;
  	}

  	vrh->little_endian = (features & (1ULL << VIRTIO_F_VERSION_1));

  	vrh->event_indices = (features & (1 << VIRTIO_RING_F_EVENT_IDX));
  	vrh->weak_barriers = weak_barriers;
  	vrh->completed = 0;
  	vrh->last_avail_idx = 0;
  	vrh->last_used_idx = 0;
  	vrh->vring.num = num;
  	vrh->vring.desc = desc;
  	vrh->vring.avail = avail;
  	vrh->vring.used = used;
  	return 0;
  }
  EXPORT_SYMBOL(vringh_init_kern);
  
  /**
   * vringh_getdesc_kern - get next available descriptor from kernelspace ring.
   * @vrh: the kernelspace vring.
   * @riov: where to put the readable descriptors (or NULL)
   * @wiov: where to put the writable descriptors (or NULL)
   * @head: head index we received, for passing to vringh_complete_kern().
   * @gfp: flags for allocating larger riov/wiov.
   *
   * Returns 0 if there was no descriptor, 1 if there was, or -errno.
   *
   * Note that on error return, you can tell the difference between an
   * invalid ring and a single invalid descriptor: in the former case,
   * *head will be vrh->vring.num.  You may be able to ignore an invalid
   * descriptor, but there's not much you can do with an invalid ring.
   *
   * Note that you may need to clean up riov and wiov, even on error!
   */
  int vringh_getdesc_kern(struct vringh *vrh,
  			struct vringh_kiov *riov,
  			struct vringh_kiov *wiov,
  			u16 *head,
  			gfp_t gfp)
  {
  	int err;
  
  	err = __vringh_get_head(vrh, getu16_kern, &vrh->last_avail_idx);
  	if (err < 0)
  		return err;
  
  	/* Empty... */
  	if (err == vrh->vring.num)
  		return 0;
  
  	*head = err;
  	err = __vringh_iov(vrh, *head, riov, wiov, no_range_check, NULL,
  			   gfp, copydesc_kern);
  	if (err)
  		return err;
  
  	return 1;
  }
  EXPORT_SYMBOL(vringh_getdesc_kern);
  
  /**
   * vringh_iov_pull_kern - copy bytes from vring_iov.
   * @riov: the riov as passed to vringh_getdesc_kern() (updated as we consume)
   * @dst: the place to copy.
   * @len: the maximum length to copy.
   *
   * Returns the bytes copied <= len or a negative errno.
   */
  ssize_t vringh_iov_pull_kern(struct vringh_kiov *riov, void *dst, size_t len)
  {
  	return vringh_iov_xfer(riov, dst, len, xfer_kern);
  }
  EXPORT_SYMBOL(vringh_iov_pull_kern);
  
  /**
   * vringh_iov_push_kern - copy bytes into vring_iov.
   * @wiov: the wiov as passed to vringh_getdesc_kern() (updated as we consume)
   * @dst: the place to copy.
   * @len: the maximum length to copy.
   *
   * Returns the bytes copied <= len or a negative errno.
   */
  ssize_t vringh_iov_push_kern(struct vringh_kiov *wiov,
  			     const void *src, size_t len)
  {
  	return vringh_iov_xfer(wiov, (void *)src, len, xfer_kern);
  }
  EXPORT_SYMBOL(vringh_iov_push_kern);
  
  /**
   * vringh_abandon_kern - we've decided not to handle the descriptor(s).
   * @vrh: the vring.
   * @num: the number of descriptors to put back (ie. num
   *	 vringh_get_kern() to undo).
   *
   * The next vringh_get_kern() will return the old descriptor(s) again.
   */
  void vringh_abandon_kern(struct vringh *vrh, unsigned int num)
  {
  	/* We only update vring_avail_event(vr) when we want to be notified,
  	 * so we haven't changed that yet. */
  	vrh->last_avail_idx -= num;
  }
  EXPORT_SYMBOL(vringh_abandon_kern);
  
  /**
   * vringh_complete_kern - we've finished with descriptor, publish it.
   * @vrh: the vring.
   * @head: the head as filled in by vringh_getdesc_kern.
   * @len: the length of data we have written.
   *
   * You should check vringh_need_notify_kern() after one or more calls
   * to this function.
   */
  int vringh_complete_kern(struct vringh *vrh, u16 head, u32 len)
  {
  	struct vring_used_elem used;

  	used.id = cpu_to_vringh32(vrh, head);
  	used.len = cpu_to_vringh32(vrh, len);

  
  	return __vringh_complete(vrh, &used, 1, putu16_kern, putused_kern);
  }
  EXPORT_SYMBOL(vringh_complete_kern);
  
  /**
   * vringh_notify_enable_kern - we want to know if something changes.
   * @vrh: the vring.
   *
   * This always enables notifications, but returns false if there are
   * now more buffers available in the vring.
   */
  bool vringh_notify_enable_kern(struct vringh *vrh)
  {
  	return __vringh_notify_enable(vrh, getu16_kern, putu16_kern);
  }
  EXPORT_SYMBOL(vringh_notify_enable_kern);
  
  /**
   * vringh_notify_disable_kern - don't tell us if something changes.
   * @vrh: the vring.
   *
   * This is our normal running state: we disable and then only enable when
   * we're going to sleep.
   */
  void vringh_notify_disable_kern(struct vringh *vrh)
  {
  	__vringh_notify_disable(vrh, putu16_kern);
  }
  EXPORT_SYMBOL(vringh_notify_disable_kern);
  
  /**
   * vringh_need_notify_kern - must we tell the other side about used buffers?
   * @vrh: the vring we've called vringh_complete_kern() on.
   *
   * Returns -errno or 0 if we don't need to tell the other side, 1 if we do.
   */
  int vringh_need_notify_kern(struct vringh *vrh)
  {
  	return __vringh_need_notify(vrh, getu16_kern);
  }
  EXPORT_SYMBOL(vringh_need_notify_kern);

  
  MODULE_LICENSE("GPL");