#include <linux/export.h>
  #include <linux/uio.h>
  #include <linux/pagemap.h>

  #include <linux/slab.h>
  #include <linux/vmalloc.h>

  static size_t copy_to_iter_iovec(void *from, size_t bytes, struct iov_iter *i)
  {
  	size_t skip, copy, left, wanted;
  	const struct iovec *iov;
  	char __user *buf;
  
  	if (unlikely(bytes > i->count))
  		bytes = i->count;
  
  	if (unlikely(!bytes))
  		return 0;
  
  	wanted = bytes;
  	iov = i->iov;
  	skip = i->iov_offset;
  	buf = iov->iov_base + skip;
  	copy = min(bytes, iov->iov_len - skip);
  
  	left = __copy_to_user(buf, from, copy);
  	copy -= left;
  	skip += copy;
  	from += copy;
  	bytes -= copy;
  	while (unlikely(!left && bytes)) {
  		iov++;
  		buf = iov->iov_base;
  		copy = min(bytes, iov->iov_len);
  		left = __copy_to_user(buf, from, copy);
  		copy -= left;
  		skip = copy;
  		from += copy;
  		bytes -= copy;
  	}
  
  	if (skip == iov->iov_len) {
  		iov++;
  		skip = 0;
  	}
  	i->count -= wanted - bytes;
  	i->nr_segs -= iov - i->iov;
  	i->iov = iov;
  	i->iov_offset = skip;
  	return wanted - bytes;
  }
  
  static size_t copy_from_iter_iovec(void *to, size_t bytes, struct iov_iter *i)
  {
  	size_t skip, copy, left, wanted;
  	const struct iovec *iov;
  	char __user *buf;
  
  	if (unlikely(bytes > i->count))
  		bytes = i->count;
  
  	if (unlikely(!bytes))
  		return 0;
  
  	wanted = bytes;
  	iov = i->iov;
  	skip = i->iov_offset;
  	buf = iov->iov_base + skip;
  	copy = min(bytes, iov->iov_len - skip);
  
  	left = __copy_from_user(to, buf, copy);
  	copy -= left;
  	skip += copy;
  	to += copy;
  	bytes -= copy;
  	while (unlikely(!left && bytes)) {
  		iov++;
  		buf = iov->iov_base;
  		copy = min(bytes, iov->iov_len);
  		left = __copy_from_user(to, buf, copy);
  		copy -= left;
  		skip = copy;
  		to += copy;
  		bytes -= copy;
  	}
  
  	if (skip == iov->iov_len) {
  		iov++;
  		skip = 0;
  	}
  	i->count -= wanted - bytes;
  	i->nr_segs -= iov - i->iov;
  	i->iov = iov;
  	i->iov_offset = skip;
  	return wanted - bytes;
  }

  static size_t copy_page_to_iter_iovec(struct page *page, size_t offset, size_t bytes,

  			 struct iov_iter *i)
  {
  	size_t skip, copy, left, wanted;
  	const struct iovec *iov;
  	char __user *buf;
  	void *kaddr, *from;
  
  	if (unlikely(bytes > i->count))
  		bytes = i->count;
  
  	if (unlikely(!bytes))
  		return 0;
  
  	wanted = bytes;
  	iov = i->iov;
  	skip = i->iov_offset;
  	buf = iov->iov_base + skip;
  	copy = min(bytes, iov->iov_len - skip);
  
  	if (!fault_in_pages_writeable(buf, copy)) {
  		kaddr = kmap_atomic(page);
  		from = kaddr + offset;
  
  		/* first chunk, usually the only one */
  		left = __copy_to_user_inatomic(buf, from, copy);
  		copy -= left;
  		skip += copy;
  		from += copy;
  		bytes -= copy;
  
  		while (unlikely(!left && bytes)) {
  			iov++;
  			buf = iov->iov_base;
  			copy = min(bytes, iov->iov_len);
  			left = __copy_to_user_inatomic(buf, from, copy);
  			copy -= left;
  			skip = copy;
  			from += copy;
  			bytes -= copy;
  		}
  		if (likely(!bytes)) {
  			kunmap_atomic(kaddr);
  			goto done;
  		}
  		offset = from - kaddr;
  		buf += copy;
  		kunmap_atomic(kaddr);
  		copy = min(bytes, iov->iov_len - skip);
  	}
  	/* Too bad - revert to non-atomic kmap */
  	kaddr = kmap(page);
  	from = kaddr + offset;
  	left = __copy_to_user(buf, from, copy);
  	copy -= left;
  	skip += copy;
  	from += copy;
  	bytes -= copy;
  	while (unlikely(!left && bytes)) {
  		iov++;
  		buf = iov->iov_base;
  		copy = min(bytes, iov->iov_len);
  		left = __copy_to_user(buf, from, copy);
  		copy -= left;
  		skip = copy;
  		from += copy;
  		bytes -= copy;
  	}
  	kunmap(page);
  done:

  	if (skip == iov->iov_len) {
  		iov++;
  		skip = 0;
  	}

  	i->count -= wanted - bytes;
  	i->nr_segs -= iov - i->iov;
  	i->iov = iov;
  	i->iov_offset = skip;
  	return wanted - bytes;
  }

  static size_t copy_page_from_iter_iovec(struct page *page, size_t offset, size_t bytes,

  			 struct iov_iter *i)
  {
  	size_t skip, copy, left, wanted;
  	const struct iovec *iov;
  	char __user *buf;
  	void *kaddr, *to;
  
  	if (unlikely(bytes > i->count))
  		bytes = i->count;
  
  	if (unlikely(!bytes))
  		return 0;
  
  	wanted = bytes;
  	iov = i->iov;
  	skip = i->iov_offset;
  	buf = iov->iov_base + skip;
  	copy = min(bytes, iov->iov_len - skip);
  
  	if (!fault_in_pages_readable(buf, copy)) {
  		kaddr = kmap_atomic(page);
  		to = kaddr + offset;
  
  		/* first chunk, usually the only one */
  		left = __copy_from_user_inatomic(to, buf, copy);
  		copy -= left;
  		skip += copy;
  		to += copy;
  		bytes -= copy;
  
  		while (unlikely(!left && bytes)) {
  			iov++;
  			buf = iov->iov_base;
  			copy = min(bytes, iov->iov_len);
  			left = __copy_from_user_inatomic(to, buf, copy);
  			copy -= left;
  			skip = copy;
  			to += copy;
  			bytes -= copy;
  		}
  		if (likely(!bytes)) {
  			kunmap_atomic(kaddr);
  			goto done;
  		}
  		offset = to - kaddr;
  		buf += copy;
  		kunmap_atomic(kaddr);
  		copy = min(bytes, iov->iov_len - skip);
  	}
  	/* Too bad - revert to non-atomic kmap */
  	kaddr = kmap(page);
  	to = kaddr + offset;
  	left = __copy_from_user(to, buf, copy);
  	copy -= left;
  	skip += copy;
  	to += copy;
  	bytes -= copy;
  	while (unlikely(!left && bytes)) {
  		iov++;
  		buf = iov->iov_base;
  		copy = min(bytes, iov->iov_len);
  		left = __copy_from_user(to, buf, copy);
  		copy -= left;
  		skip = copy;
  		to += copy;
  		bytes -= copy;
  	}
  	kunmap(page);
  done:

  	if (skip == iov->iov_len) {
  		iov++;
  		skip = 0;
  	}

  	i->count -= wanted - bytes;
  	i->nr_segs -= iov - i->iov;
  	i->iov = iov;
  	i->iov_offset = skip;
  	return wanted - bytes;
  }

  static size_t zero_iovec(size_t bytes, struct iov_iter *i)
  {
  	size_t skip, copy, left, wanted;
  	const struct iovec *iov;
  	char __user *buf;
  
  	if (unlikely(bytes > i->count))
  		bytes = i->count;
  
  	if (unlikely(!bytes))
  		return 0;
  
  	wanted = bytes;
  	iov = i->iov;
  	skip = i->iov_offset;
  	buf = iov->iov_base + skip;
  	copy = min(bytes, iov->iov_len - skip);
  
  	left = __clear_user(buf, copy);
  	copy -= left;
  	skip += copy;
  	bytes -= copy;
  
  	while (unlikely(!left && bytes)) {
  		iov++;
  		buf = iov->iov_base;
  		copy = min(bytes, iov->iov_len);
  		left = __clear_user(buf, copy);
  		copy -= left;
  		skip = copy;
  		bytes -= copy;
  	}
  
  	if (skip == iov->iov_len) {
  		iov++;
  		skip = 0;
  	}
  	i->count -= wanted - bytes;
  	i->nr_segs -= iov - i->iov;
  	i->iov = iov;
  	i->iov_offset = skip;
  	return wanted - bytes;
  }

  static size_t __iovec_copy_from_user_inatomic(char *vaddr,
  			const struct iovec *iov, size_t base, size_t bytes)
  {
  	size_t copied = 0, left = 0;
  
  	while (bytes) {
  		char __user *buf = iov->iov_base + base;
  		int copy = min(bytes, iov->iov_len - base);
  
  		base = 0;
  		left = __copy_from_user_inatomic(vaddr, buf, copy);
  		copied += copy;
  		bytes -= copy;
  		vaddr += copy;
  		iov++;
  
  		if (unlikely(left))
  			break;
  	}
  	return copied - left;
  }
  
  /*
   * Copy as much as we can into the page and return the number of bytes which
   * were successfully copied.  If a fault is encountered then return the number of
   * bytes which were copied.
   */

  static size_t copy_from_user_atomic_iovec(struct page *page,

  		struct iov_iter *i, unsigned long offset, size_t bytes)
  {
  	char *kaddr;
  	size_t copied;
  
  	kaddr = kmap_atomic(page);
  	if (likely(i->nr_segs == 1)) {
  		int left;
  		char __user *buf = i->iov->iov_base + i->iov_offset;
  		left = __copy_from_user_inatomic(kaddr + offset, buf, bytes);
  		copied = bytes - left;
  	} else {
  		copied = __iovec_copy_from_user_inatomic(kaddr + offset,
  						i->iov, i->iov_offset, bytes);
  	}
  	kunmap_atomic(kaddr);
  
  	return copied;
  }

  static void advance_iovec(struct iov_iter *i, size_t bytes)

  {
  	BUG_ON(i->count < bytes);
  
  	if (likely(i->nr_segs == 1)) {
  		i->iov_offset += bytes;
  		i->count -= bytes;
  	} else {
  		const struct iovec *iov = i->iov;
  		size_t base = i->iov_offset;
  		unsigned long nr_segs = i->nr_segs;
  
  		/*
  		 * The !iov->iov_len check ensures we skip over unlikely
  		 * zero-length segments (without overruning the iovec).
  		 */
  		while (bytes || unlikely(i->count && !iov->iov_len)) {
  			int copy;
  
  			copy = min(bytes, iov->iov_len - base);
  			BUG_ON(!i->count || i->count < copy);
  			i->count -= copy;
  			bytes -= copy;
  			base += copy;
  			if (iov->iov_len == base) {
  				iov++;
  				nr_segs--;
  				base = 0;
  			}
  		}
  		i->iov = iov;
  		i->iov_offset = base;
  		i->nr_segs = nr_segs;
  	}
  }

  
  /*
   * Fault in the first iovec of the given iov_iter, to a maximum length
   * of bytes. Returns 0 on success, or non-zero if the memory could not be
   * accessed (ie. because it is an invalid address).
   *
   * writev-intensive code may want this to prefault several iovecs -- that
   * would be possible (callers must not rely on the fact that _only_ the
   * first iovec will be faulted with the current implementation).
   */
  int iov_iter_fault_in_readable(struct iov_iter *i, size_t bytes)
  {

  	if (!(i->type & ITER_BVEC)) {
  		char __user *buf = i->iov->iov_base + i->iov_offset;
  		bytes = min(bytes, i->iov->iov_len - i->iov_offset);
  		return fault_in_pages_readable(buf, bytes);
  	}
  	return 0;

  }
  EXPORT_SYMBOL(iov_iter_fault_in_readable);

  static unsigned long alignment_iovec(const struct iov_iter *i)

  {
  	const struct iovec *iov = i->iov;
  	unsigned long res;
  	size_t size = i->count;
  	size_t n;
  
  	if (!size)
  		return 0;
  
  	res = (unsigned long)iov->iov_base + i->iov_offset;
  	n = iov->iov_len - i->iov_offset;
  	if (n >= size)
  		return res | size;
  	size -= n;
  	res |= n;
  	while (size > (++iov)->iov_len) {
  		res |= (unsigned long)iov->iov_base | iov->iov_len;
  		size -= iov->iov_len;
  	}
  	res |= (unsigned long)iov->iov_base | size;
  	return res;
  }

  
  void iov_iter_init(struct iov_iter *i, int direction,
  			const struct iovec *iov, unsigned long nr_segs,
  			size_t count)
  {
  	/* It will get better.  Eventually... */
  	if (segment_eq(get_fs(), KERNEL_DS))

  		direction |= ITER_KVEC;

  	i->type = direction;
  	i->iov = iov;
  	i->nr_segs = nr_segs;
  	i->iov_offset = 0;
  	i->count = count;
  }
  EXPORT_SYMBOL(iov_iter_init);

  static ssize_t get_pages_iovec(struct iov_iter *i,

  		   struct page **pages, size_t maxsize, unsigned maxpages,

  		   size_t *start)
  {
  	size_t offset = i->iov_offset;
  	const struct iovec *iov = i->iov;
  	size_t len;
  	unsigned long addr;
  	int n;
  	int res;
  
  	len = iov->iov_len - offset;
  	if (len > i->count)
  		len = i->count;

  	if (len > maxsize)
  		len = maxsize;

  	addr = (unsigned long)iov->iov_base + offset;
  	len += *start = addr & (PAGE_SIZE - 1);

  	if (len > maxpages * PAGE_SIZE)
  		len = maxpages * PAGE_SIZE;

  	addr &= ~(PAGE_SIZE - 1);
  	n = (len + PAGE_SIZE - 1) / PAGE_SIZE;
  	res = get_user_pages_fast(addr, n, (i->type & WRITE) != WRITE, pages);
  	if (unlikely(res < 0))
  		return res;
  	return (res == n ? len : res * PAGE_SIZE) - *start;
  }

  static ssize_t get_pages_alloc_iovec(struct iov_iter *i,

  		   struct page ***pages, size_t maxsize,
  		   size_t *start)
  {
  	size_t offset = i->iov_offset;
  	const struct iovec *iov = i->iov;
  	size_t len;
  	unsigned long addr;
  	void *p;
  	int n;
  	int res;
  
  	len = iov->iov_len - offset;
  	if (len > i->count)
  		len = i->count;
  	if (len > maxsize)
  		len = maxsize;
  	addr = (unsigned long)iov->iov_base + offset;
  	len += *start = addr & (PAGE_SIZE - 1);
  	addr &= ~(PAGE_SIZE - 1);
  	n = (len + PAGE_SIZE - 1) / PAGE_SIZE;
  	
  	p = kmalloc(n * sizeof(struct page *), GFP_KERNEL);
  	if (!p)
  		p = vmalloc(n * sizeof(struct page *));
  	if (!p)
  		return -ENOMEM;
  
  	res = get_user_pages_fast(addr, n, (i->type & WRITE) != WRITE, p);
  	if (unlikely(res < 0)) {
  		kvfree(p);
  		return res;
  	}
  	*pages = p;
  	return (res == n ? len : res * PAGE_SIZE) - *start;
  }

  static int iov_iter_npages_iovec(const struct iov_iter *i, int maxpages)

  {
  	size_t offset = i->iov_offset;
  	size_t size = i->count;
  	const struct iovec *iov = i->iov;
  	int npages = 0;
  	int n;
  
  	for (n = 0; size && n < i->nr_segs; n++, iov++) {
  		unsigned long addr = (unsigned long)iov->iov_base + offset;
  		size_t len = iov->iov_len - offset;
  		offset = 0;
  		if (unlikely(!len))	/* empty segment */
  			continue;
  		if (len > size)
  			len = size;
  		npages += (addr + len + PAGE_SIZE - 1) / PAGE_SIZE
  			  - addr / PAGE_SIZE;
  		if (npages >= maxpages)	/* don't bother going further */
  			return maxpages;
  		size -= len;
  		offset = 0;
  	}
  	return min(npages, maxpages);
  }

  
  static void memcpy_from_page(char *to, struct page *page, size_t offset, size_t len)
  {
  	char *from = kmap_atomic(page);
  	memcpy(to, from + offset, len);
  	kunmap_atomic(from);
  }
  
  static void memcpy_to_page(struct page *page, size_t offset, char *from, size_t len)
  {
  	char *to = kmap_atomic(page);
  	memcpy(to + offset, from, len);
  	kunmap_atomic(to);
  }

  static void memzero_page(struct page *page, size_t offset, size_t len)
  {
  	char *addr = kmap_atomic(page);
  	memset(addr + offset, 0, len);
  	kunmap_atomic(addr);
  }
  
  static size_t copy_to_iter_bvec(void *from, size_t bytes, struct iov_iter *i)

  {
  	size_t skip, copy, wanted;
  	const struct bio_vec *bvec;

  
  	if (unlikely(bytes > i->count))
  		bytes = i->count;
  
  	if (unlikely(!bytes))
  		return 0;
  
  	wanted = bytes;
  	bvec = i->bvec;
  	skip = i->iov_offset;
  	copy = min_t(size_t, bytes, bvec->bv_len - skip);

  	memcpy_to_page(bvec->bv_page, skip + bvec->bv_offset, from, copy);
  	skip += copy;
  	from += copy;
  	bytes -= copy;
  	while (bytes) {
  		bvec++;
  		copy = min(bytes, (size_t)bvec->bv_len);
  		memcpy_to_page(bvec->bv_page, bvec->bv_offset, from, copy);
  		skip = copy;
  		from += copy;
  		bytes -= copy;
  	}

  	if (skip == bvec->bv_len) {
  		bvec++;
  		skip = 0;
  	}
  	i->count -= wanted - bytes;
  	i->nr_segs -= bvec - i->bvec;
  	i->bvec = bvec;
  	i->iov_offset = skip;
  	return wanted - bytes;
  }

  static size_t copy_from_iter_bvec(void *to, size_t bytes, struct iov_iter *i)

  {
  	size_t skip, copy, wanted;
  	const struct bio_vec *bvec;

  
  	if (unlikely(bytes > i->count))
  		bytes = i->count;
  
  	if (unlikely(!bytes))
  		return 0;
  
  	wanted = bytes;
  	bvec = i->bvec;
  	skip = i->iov_offset;

  	copy = min(bytes, bvec->bv_len - skip);
  
  	memcpy_from_page(to, bvec->bv_page, bvec->bv_offset + skip, copy);
  
  	to += copy;
  	skip += copy;
  	bytes -= copy;
  
  	while (bytes) {
  		bvec++;
  		copy = min(bytes, (size_t)bvec->bv_len);
  		memcpy_from_page(to, bvec->bv_page, bvec->bv_offset, copy);
  		skip = copy;
  		to += copy;
  		bytes -= copy;
  	}

  	if (skip == bvec->bv_len) {
  		bvec++;
  		skip = 0;
  	}
  	i->count -= wanted;
  	i->nr_segs -= bvec - i->bvec;
  	i->bvec = bvec;
  	i->iov_offset = skip;
  	return wanted;
  }

  static size_t copy_page_to_iter_bvec(struct page *page, size_t offset,
  					size_t bytes, struct iov_iter *i)
  {
  	void *kaddr = kmap_atomic(page);
  	size_t wanted = copy_to_iter_bvec(kaddr + offset, bytes, i);
  	kunmap_atomic(kaddr);
  	return wanted;
  }
  
  static size_t copy_page_from_iter_bvec(struct page *page, size_t offset,
  					size_t bytes, struct iov_iter *i)
  {
  	void *kaddr = kmap_atomic(page);
  	size_t wanted = copy_from_iter_bvec(kaddr + offset, bytes, i);
  	kunmap_atomic(kaddr);
  	return wanted;
  }
  
  static size_t zero_bvec(size_t bytes, struct iov_iter *i)
  {
  	size_t skip, copy, wanted;
  	const struct bio_vec *bvec;
  
  	if (unlikely(bytes > i->count))
  		bytes = i->count;
  
  	if (unlikely(!bytes))
  		return 0;
  
  	wanted = bytes;
  	bvec = i->bvec;
  	skip = i->iov_offset;
  	copy = min_t(size_t, bytes, bvec->bv_len - skip);
  
  	memzero_page(bvec->bv_page, skip + bvec->bv_offset, copy);
  	skip += copy;
  	bytes -= copy;
  	while (bytes) {
  		bvec++;
  		copy = min(bytes, (size_t)bvec->bv_len);
  		memzero_page(bvec->bv_page, bvec->bv_offset, copy);
  		skip = copy;
  		bytes -= copy;
  	}
  	if (skip == bvec->bv_len) {
  		bvec++;
  		skip = 0;
  	}
  	i->count -= wanted - bytes;
  	i->nr_segs -= bvec - i->bvec;
  	i->bvec = bvec;
  	i->iov_offset = skip;
  	return wanted - bytes;
  }

  static size_t copy_from_user_bvec(struct page *page,
  		struct iov_iter *i, unsigned long offset, size_t bytes)
  {
  	char *kaddr;
  	size_t left;
  	const struct bio_vec *bvec;
  	size_t base = i->iov_offset;
  
  	kaddr = kmap_atomic(page);
  	for (left = bytes, bvec = i->bvec; left; bvec++, base = 0) {
  		size_t copy = min(left, bvec->bv_len - base);
  		if (!bvec->bv_len)
  			continue;
  		memcpy_from_page(kaddr + offset, bvec->bv_page,
  				 bvec->bv_offset + base, copy);
  		offset += copy;
  		left -= copy;
  	}
  	kunmap_atomic(kaddr);
  	return bytes;
  }
  
  static void advance_bvec(struct iov_iter *i, size_t bytes)
  {
  	BUG_ON(i->count < bytes);
  
  	if (likely(i->nr_segs == 1)) {
  		i->iov_offset += bytes;
  		i->count -= bytes;
  	} else {
  		const struct bio_vec *bvec = i->bvec;
  		size_t base = i->iov_offset;
  		unsigned long nr_segs = i->nr_segs;
  
  		/*
  		 * The !iov->iov_len check ensures we skip over unlikely
  		 * zero-length segments (without overruning the iovec).
  		 */
  		while (bytes || unlikely(i->count && !bvec->bv_len)) {
  			int copy;
  
  			copy = min(bytes, bvec->bv_len - base);
  			BUG_ON(!i->count || i->count < copy);
  			i->count -= copy;
  			bytes -= copy;
  			base += copy;
  			if (bvec->bv_len == base) {
  				bvec++;
  				nr_segs--;
  				base = 0;
  			}
  		}
  		i->bvec = bvec;
  		i->iov_offset = base;
  		i->nr_segs = nr_segs;
  	}
  }
  
  static unsigned long alignment_bvec(const struct iov_iter *i)
  {
  	const struct bio_vec *bvec = i->bvec;
  	unsigned long res;
  	size_t size = i->count;
  	size_t n;
  
  	if (!size)
  		return 0;
  
  	res = bvec->bv_offset + i->iov_offset;
  	n = bvec->bv_len - i->iov_offset;
  	if (n >= size)
  		return res | size;
  	size -= n;
  	res |= n;
  	while (size > (++bvec)->bv_len) {
  		res |= bvec->bv_offset | bvec->bv_len;
  		size -= bvec->bv_len;
  	}
  	res |= bvec->bv_offset | size;
  	return res;
  }
  
  static ssize_t get_pages_bvec(struct iov_iter *i,

  		   struct page **pages, size_t maxsize, unsigned maxpages,

  		   size_t *start)
  {
  	const struct bio_vec *bvec = i->bvec;
  	size_t len = bvec->bv_len - i->iov_offset;
  	if (len > i->count)
  		len = i->count;

  	if (len > maxsize)
  		len = maxsize;

  	/* can't be more than PAGE_SIZE */

  	*start = bvec->bv_offset + i->iov_offset;
  
  	get_page(*pages = bvec->bv_page);
  
  	return len;
  }
  
  static ssize_t get_pages_alloc_bvec(struct iov_iter *i,
  		   struct page ***pages, size_t maxsize,
  		   size_t *start)
  {
  	const struct bio_vec *bvec = i->bvec;
  	size_t len = bvec->bv_len - i->iov_offset;
  	if (len > i->count)
  		len = i->count;
  	if (len > maxsize)
  		len = maxsize;
  	*start = bvec->bv_offset + i->iov_offset;
  
  	*pages = kmalloc(sizeof(struct page *), GFP_KERNEL);
  	if (!*pages)
  		return -ENOMEM;
  
  	get_page(**pages = bvec->bv_page);
  
  	return len;
  }
  
  static int iov_iter_npages_bvec(const struct iov_iter *i, int maxpages)
  {
  	size_t offset = i->iov_offset;
  	size_t size = i->count;
  	const struct bio_vec *bvec = i->bvec;
  	int npages = 0;
  	int n;
  
  	for (n = 0; size && n < i->nr_segs; n++, bvec++) {
  		size_t len = bvec->bv_len - offset;
  		offset = 0;
  		if (unlikely(!len))	/* empty segment */
  			continue;
  		if (len > size)
  			len = size;
  		npages++;
  		if (npages >= maxpages)	/* don't bother going further */
  			return maxpages;
  		size -= len;
  		offset = 0;
  	}
  	return min(npages, maxpages);
  }
  
  size_t copy_page_to_iter(struct page *page, size_t offset, size_t bytes,
  			 struct iov_iter *i)
  {
  	if (i->type & ITER_BVEC)
  		return copy_page_to_iter_bvec(page, offset, bytes, i);
  	else
  		return copy_page_to_iter_iovec(page, offset, bytes, i);
  }
  EXPORT_SYMBOL(copy_page_to_iter);
  
  size_t copy_page_from_iter(struct page *page, size_t offset, size_t bytes,
  			 struct iov_iter *i)
  {
  	if (i->type & ITER_BVEC)
  		return copy_page_from_iter_bvec(page, offset, bytes, i);
  	else
  		return copy_page_from_iter_iovec(page, offset, bytes, i);
  }
  EXPORT_SYMBOL(copy_page_from_iter);

  size_t copy_to_iter(void *addr, size_t bytes, struct iov_iter *i)
  {
  	if (i->type & ITER_BVEC)
  		return copy_to_iter_bvec(addr, bytes, i);
  	else
  		return copy_to_iter_iovec(addr, bytes, i);
  }
  EXPORT_SYMBOL(copy_to_iter);
  
  size_t copy_from_iter(void *addr, size_t bytes, struct iov_iter *i)
  {
  	if (i->type & ITER_BVEC)
  		return copy_from_iter_bvec(addr, bytes, i);
  	else
  		return copy_from_iter_iovec(addr, bytes, i);
  }
  EXPORT_SYMBOL(copy_from_iter);
  
  size_t iov_iter_zero(size_t bytes, struct iov_iter *i)
  {
  	if (i->type & ITER_BVEC) {
  		return zero_bvec(bytes, i);
  	} else {
  		return zero_iovec(bytes, i);
  	}
  }
  EXPORT_SYMBOL(iov_iter_zero);

  size_t iov_iter_copy_from_user_atomic(struct page *page,
  		struct iov_iter *i, unsigned long offset, size_t bytes)
  {
  	if (i->type & ITER_BVEC)
  		return copy_from_user_bvec(page, i, offset, bytes);
  	else
  		return copy_from_user_atomic_iovec(page, i, offset, bytes);
  }
  EXPORT_SYMBOL(iov_iter_copy_from_user_atomic);
  
  void iov_iter_advance(struct iov_iter *i, size_t size)
  {
  	if (i->type & ITER_BVEC)
  		advance_bvec(i, size);
  	else
  		advance_iovec(i, size);
  }
  EXPORT_SYMBOL(iov_iter_advance);
  
  /*
   * Return the count of just the current iov_iter segment.
   */
  size_t iov_iter_single_seg_count(const struct iov_iter *i)
  {
  	if (i->nr_segs == 1)
  		return i->count;
  	else if (i->type & ITER_BVEC)

  		return min(i->count, i->bvec->bv_len - i->iov_offset);

  	else
  		return min(i->count, i->iov->iov_len - i->iov_offset);

  }
  EXPORT_SYMBOL(iov_iter_single_seg_count);
  
  unsigned long iov_iter_alignment(const struct iov_iter *i)
  {
  	if (i->type & ITER_BVEC)
  		return alignment_bvec(i);
  	else
  		return alignment_iovec(i);
  }
  EXPORT_SYMBOL(iov_iter_alignment);
  
  ssize_t iov_iter_get_pages(struct iov_iter *i,

  		   struct page **pages, size_t maxsize, unsigned maxpages,

  		   size_t *start)
  {
  	if (i->type & ITER_BVEC)

  		return get_pages_bvec(i, pages, maxsize, maxpages, start);

  	else

  		return get_pages_iovec(i, pages, maxsize, maxpages, start);

  }
  EXPORT_SYMBOL(iov_iter_get_pages);
  
  ssize_t iov_iter_get_pages_alloc(struct iov_iter *i,
  		   struct page ***pages, size_t maxsize,
  		   size_t *start)
  {
  	if (i->type & ITER_BVEC)
  		return get_pages_alloc_bvec(i, pages, maxsize, start);
  	else
  		return get_pages_alloc_iovec(i, pages, maxsize, start);
  }
  EXPORT_SYMBOL(iov_iter_get_pages_alloc);
  
  int iov_iter_npages(const struct iov_iter *i, int maxpages)
  {
  	if (i->type & ITER_BVEC)
  		return iov_iter_npages_bvec(i, maxpages);
  	else
  		return iov_iter_npages_iovec(i, maxpages);
  }

  EXPORT_SYMBOL(iov_iter_npages);