#include <linux/export.h>

  #include <linux/bvec.h>

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

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

  #include <linux/splice.h>

  #include <net/checksum.h>

  #define PIPE_PARANOIA /* for now */

  #define iterate_iovec(i, n, __v, __p, skip, STEP) {	\
  	size_t left;					\
  	size_t wanted = n;				\
  	__p = i->iov;					\
  	__v.iov_len = min(n, __p->iov_len - skip);	\
  	if (likely(__v.iov_len)) {			\
  		__v.iov_base = __p->iov_base + skip;	\
  		left = (STEP);				\
  		__v.iov_len -= left;			\
  		skip += __v.iov_len;			\
  		n -= __v.iov_len;			\
  	} else {					\
  		left = 0;				\
  	}						\
  	while (unlikely(!left && n)) {			\
  		__p++;					\
  		__v.iov_len = min(n, __p->iov_len);	\
  		if (unlikely(!__v.iov_len))		\
  			continue;			\
  		__v.iov_base = __p->iov_base;		\
  		left = (STEP);				\
  		__v.iov_len -= left;			\
  		skip = __v.iov_len;			\
  		n -= __v.iov_len;			\
  	}						\
  	n = wanted - n;					\
  }

  #define iterate_kvec(i, n, __v, __p, skip, STEP) {	\
  	size_t wanted = n;				\
  	__p = i->kvec;					\
  	__v.iov_len = min(n, __p->iov_len - skip);	\
  	if (likely(__v.iov_len)) {			\
  		__v.iov_base = __p->iov_base + skip;	\
  		(void)(STEP);				\
  		skip += __v.iov_len;			\
  		n -= __v.iov_len;			\
  	}						\
  	while (unlikely(n)) {				\
  		__p++;					\
  		__v.iov_len = min(n, __p->iov_len);	\
  		if (unlikely(!__v.iov_len))		\
  			continue;			\
  		__v.iov_base = __p->iov_base;		\
  		(void)(STEP);				\
  		skip = __v.iov_len;			\
  		n -= __v.iov_len;			\
  	}						\
  	n = wanted;					\
  }

  #define iterate_bvec(i, n, __v, __bi, skip, STEP) {	\
  	struct bvec_iter __start;			\
  	__start.bi_size = n;				\
  	__start.bi_bvec_done = skip;			\
  	__start.bi_idx = 0;				\
  	for_each_bvec(__v, i->bvec, __bi, __start) {	\
  		if (!__v.bv_len)			\

  			continue;			\

  		(void)(STEP);				\

  	}						\

  }

  #define iterate_all_kinds(i, n, v, I, B, K) {			\

  	if (likely(n)) {					\
  		size_t skip = i->iov_offset;			\
  		if (unlikely(i->type & ITER_BVEC)) {		\
  			struct bio_vec v;			\
  			struct bvec_iter __bi;			\
  			iterate_bvec(i, n, v, __bi, skip, (B))	\
  		} else if (unlikely(i->type & ITER_KVEC)) {	\
  			const struct kvec *kvec;		\
  			struct kvec v;				\
  			iterate_kvec(i, n, v, kvec, skip, (K))	\
  		} else {					\
  			const struct iovec *iov;		\
  			struct iovec v;				\
  			iterate_iovec(i, n, v, iov, skip, (I))	\
  		}						\

  	}							\
  }

  #define iterate_and_advance(i, n, v, I, B, K) {			\

  	if (unlikely(i->count < n))				\
  		n = i->count;					\

  	if (i->count) {						\

  		size_t skip = i->iov_offset;			\
  		if (unlikely(i->type & ITER_BVEC)) {		\

  			const struct bio_vec *bvec = i->bvec;	\

  			struct bio_vec v;			\

  			struct bvec_iter __bi;			\
  			iterate_bvec(i, n, v, __bi, skip, (B))	\
  			i->bvec = __bvec_iter_bvec(i->bvec, __bi);	\
  			i->nr_segs -= i->bvec - bvec;		\
  			skip = __bi.bi_bvec_done;		\

  		} else if (unlikely(i->type & ITER_KVEC)) {	\
  			const struct kvec *kvec;		\
  			struct kvec v;				\
  			iterate_kvec(i, n, v, kvec, skip, (K))	\
  			if (skip == kvec->iov_len) {		\
  				kvec++;				\
  				skip = 0;			\
  			}					\
  			i->nr_segs -= kvec - i->kvec;		\
  			i->kvec = kvec;				\
  		} else {					\
  			const struct iovec *iov;		\
  			struct iovec v;				\
  			iterate_iovec(i, n, v, iov, skip, (I))	\
  			if (skip == iov->iov_len) {		\
  				iov++;				\
  				skip = 0;			\
  			}					\
  			i->nr_segs -= iov - i->iov;		\
  			i->iov = iov;				\

  		}						\

  		i->count -= n;					\
  		i->iov_offset = skip;				\

  	}							\

  }

  static int copyout(void __user *to, const void *from, size_t n)
  {
  	if (access_ok(VERIFY_WRITE, to, n)) {
  		kasan_check_read(from, n);
  		n = raw_copy_to_user(to, from, n);
  	}
  	return n;
  }
  
  static int copyin(void *to, const void __user *from, size_t n)
  {
  	if (access_ok(VERIFY_READ, from, n)) {
  		kasan_check_write(to, n);
  		n = raw_copy_from_user(to, from, n);
  	}
  	return n;
  }

  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;

  	might_fault();

  	wanted = bytes;
  	iov = i->iov;
  	skip = i->iov_offset;
  	buf = iov->iov_base + skip;
  	copy = min(bytes, iov->iov_len - skip);

  	if (IS_ENABLED(CONFIG_HIGHMEM) && !fault_in_pages_writeable(buf, copy)) {

  		kaddr = kmap_atomic(page);
  		from = kaddr + offset;
  
  		/* first chunk, usually the only one */

  		left = copyout(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 = copyout(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 = copyout(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 = copyout(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;

  	might_fault();

  	wanted = bytes;
  	iov = i->iov;
  	skip = i->iov_offset;
  	buf = iov->iov_base + skip;
  	copy = min(bytes, iov->iov_len - skip);

  	if (IS_ENABLED(CONFIG_HIGHMEM) && !fault_in_pages_readable(buf, copy)) {

  		kaddr = kmap_atomic(page);
  		to = kaddr + offset;
  
  		/* first chunk, usually the only one */

  		left = copyin(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 = copyin(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 = copyin(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 = copyin(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;
  }

  #ifdef PIPE_PARANOIA
  static bool sanity(const struct iov_iter *i)
  {
  	struct pipe_inode_info *pipe = i->pipe;
  	int idx = i->idx;
  	int next = pipe->curbuf + pipe->nrbufs;
  	if (i->iov_offset) {
  		struct pipe_buffer *p;
  		if (unlikely(!pipe->nrbufs))
  			goto Bad;	// pipe must be non-empty
  		if (unlikely(idx != ((next - 1) & (pipe->buffers - 1))))
  			goto Bad;	// must be at the last buffer...
  
  		p = &pipe->bufs[idx];
  		if (unlikely(p->offset + p->len != i->iov_offset))
  			goto Bad;	// ... at the end of segment
  	} else {
  		if (idx != (next & (pipe->buffers - 1)))
  			goto Bad;	// must be right after the last buffer
  	}
  	return true;
  Bad:
  	printk(KERN_ERR "idx = %d, offset = %zd
  ", i->idx, i->iov_offset);
  	printk(KERN_ERR "curbuf = %d, nrbufs = %d, buffers = %d
  ",
  			pipe->curbuf, pipe->nrbufs, pipe->buffers);
  	for (idx = 0; idx < pipe->buffers; idx++)
  		printk(KERN_ERR "[%p %p %d %d]
  ",
  			pipe->bufs[idx].ops,
  			pipe->bufs[idx].page,
  			pipe->bufs[idx].offset,
  			pipe->bufs[idx].len);
  	WARN_ON(1);
  	return false;
  }
  #else
  #define sanity(i) true
  #endif
  
  static inline int next_idx(int idx, struct pipe_inode_info *pipe)
  {
  	return (idx + 1) & (pipe->buffers - 1);
  }
  
  static size_t copy_page_to_iter_pipe(struct page *page, size_t offset, size_t bytes,
  			 struct iov_iter *i)
  {
  	struct pipe_inode_info *pipe = i->pipe;
  	struct pipe_buffer *buf;
  	size_t off;
  	int idx;
  
  	if (unlikely(bytes > i->count))
  		bytes = i->count;
  
  	if (unlikely(!bytes))
  		return 0;
  
  	if (!sanity(i))
  		return 0;
  
  	off = i->iov_offset;
  	idx = i->idx;
  	buf = &pipe->bufs[idx];
  	if (off) {
  		if (offset == off && buf->page == page) {
  			/* merge with the last one */
  			buf->len += bytes;
  			i->iov_offset += bytes;
  			goto out;
  		}
  		idx = next_idx(idx, pipe);
  		buf = &pipe->bufs[idx];
  	}
  	if (idx == pipe->curbuf && pipe->nrbufs)
  		return 0;
  	pipe->nrbufs++;
  	buf->ops = &page_cache_pipe_buf_ops;
  	get_page(buf->page = page);
  	buf->offset = offset;
  	buf->len = bytes;
  	i->iov_offset = offset + bytes;
  	i->idx = idx;
  out:
  	i->count -= bytes;
  	return bytes;
  }

  /*

   * Fault in one or more iovecs of the given iov_iter, to a maximum length of
   * bytes.  For each iovec, fault in each page that constitutes the iovec.
   *
   * Return 0 on success, or non-zero if the memory could not be accessed (i.e.
   * because it is an invalid address).
   */

  int iov_iter_fault_in_readable(struct iov_iter *i, size_t bytes)

  {
  	size_t skip = i->iov_offset;
  	const struct iovec *iov;
  	int err;
  	struct iovec v;
  
  	if (!(i->type & (ITER_BVEC|ITER_KVEC))) {
  		iterate_iovec(i, bytes, v, iov, skip, ({

  			err = fault_in_pages_readable(v.iov_base, v.iov_len);

  			if (unlikely(err))
  			return err;
  		0;}))
  	}
  	return 0;
  }

  EXPORT_SYMBOL(iov_iter_fault_in_readable);

  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 (uaccess_kernel()) {

  		direction |= ITER_KVEC;

  		i->type = direction;
  		i->kvec = (struct kvec *)iov;
  	} else {
  		i->type = direction;
  		i->iov = iov;
  	}

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

  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, const 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 inline bool allocated(struct pipe_buffer *buf)
  {
  	return buf->ops == &default_pipe_buf_ops;
  }
  
  static inline void data_start(const struct iov_iter *i, int *idxp, size_t *offp)
  {
  	size_t off = i->iov_offset;
  	int idx = i->idx;
  	if (off && (!allocated(&i->pipe->bufs[idx]) || off == PAGE_SIZE)) {
  		idx = next_idx(idx, i->pipe);
  		off = 0;
  	}
  	*idxp = idx;
  	*offp = off;
  }
  
  static size_t push_pipe(struct iov_iter *i, size_t size,
  			int *idxp, size_t *offp)
  {
  	struct pipe_inode_info *pipe = i->pipe;
  	size_t off;
  	int idx;
  	ssize_t left;
  
  	if (unlikely(size > i->count))
  		size = i->count;
  	if (unlikely(!size))
  		return 0;
  
  	left = size;
  	data_start(i, &idx, &off);
  	*idxp = idx;
  	*offp = off;
  	if (off) {
  		left -= PAGE_SIZE - off;
  		if (left <= 0) {
  			pipe->bufs[idx].len += size;
  			return size;
  		}
  		pipe->bufs[idx].len = PAGE_SIZE;
  		idx = next_idx(idx, pipe);
  	}
  	while (idx != pipe->curbuf || !pipe->nrbufs) {
  		struct page *page = alloc_page(GFP_USER);
  		if (!page)
  			break;
  		pipe->nrbufs++;
  		pipe->bufs[idx].ops = &default_pipe_buf_ops;
  		pipe->bufs[idx].page = page;
  		pipe->bufs[idx].offset = 0;
  		if (left <= PAGE_SIZE) {
  			pipe->bufs[idx].len = left;
  			return size;
  		}
  		pipe->bufs[idx].len = PAGE_SIZE;
  		left -= PAGE_SIZE;
  		idx = next_idx(idx, pipe);
  	}
  	return size - left;
  }
  
  static size_t copy_pipe_to_iter(const void *addr, size_t bytes,
  				struct iov_iter *i)
  {
  	struct pipe_inode_info *pipe = i->pipe;
  	size_t n, off;
  	int idx;
  
  	if (!sanity(i))
  		return 0;
  
  	bytes = n = push_pipe(i, bytes, &idx, &off);
  	if (unlikely(!n))
  		return 0;
  	for ( ; n; idx = next_idx(idx, pipe), off = 0) {
  		size_t chunk = min_t(size_t, n, PAGE_SIZE - off);
  		memcpy_to_page(pipe->bufs[idx].page, off, addr, chunk);
  		i->idx = idx;
  		i->iov_offset = off + chunk;
  		n -= chunk;
  		addr += chunk;
  	}
  	i->count -= bytes;
  	return bytes;
  }

  size_t _copy_to_iter(const void *addr, size_t bytes, struct iov_iter *i)

  {

  	const char *from = addr;

  	if (unlikely(i->type & ITER_PIPE))
  		return copy_pipe_to_iter(addr, bytes, i);

  	if (iter_is_iovec(i))
  		might_fault();

  	iterate_and_advance(i, bytes, v,

  		copyout(v.iov_base, (from += v.iov_len) - v.iov_len, v.iov_len),

  		memcpy_to_page(v.bv_page, v.bv_offset,

  			       (from += v.bv_len) - v.bv_len, v.bv_len),
  		memcpy(v.iov_base, (from += v.iov_len) - v.iov_len, v.iov_len)

  	)

  	return bytes;

  }

  EXPORT_SYMBOL(_copy_to_iter);

  size_t _copy_from_iter(void *addr, size_t bytes, struct iov_iter *i)

  {

  	char *to = addr;

  	if (unlikely(i->type & ITER_PIPE)) {
  		WARN_ON(1);
  		return 0;
  	}

  	if (iter_is_iovec(i))
  		might_fault();

  	iterate_and_advance(i, bytes, v,

  		copyin((to += v.iov_len) - v.iov_len, v.iov_base, v.iov_len),

  		memcpy_from_page((to += v.bv_len) - v.bv_len, v.bv_page,

  				 v.bv_offset, v.bv_len),
  		memcpy((to += v.iov_len) - v.iov_len, v.iov_base, v.iov_len)

  	)
  
  	return bytes;

  }

  EXPORT_SYMBOL(_copy_from_iter);

  bool _copy_from_iter_full(void *addr, size_t bytes, struct iov_iter *i)

  {
  	char *to = addr;
  	if (unlikely(i->type & ITER_PIPE)) {
  		WARN_ON(1);
  		return false;
  	}

  	if (unlikely(i->count < bytes))

  		return false;

  	if (iter_is_iovec(i))
  		might_fault();

  	iterate_all_kinds(i, bytes, v, ({

  		if (copyin((to += v.iov_len) - v.iov_len,

  				      v.iov_base, v.iov_len))
  			return false;
  		0;}),
  		memcpy_from_page((to += v.bv_len) - v.bv_len, v.bv_page,
  				 v.bv_offset, v.bv_len),
  		memcpy((to += v.iov_len) - v.iov_len, v.iov_base, v.iov_len)
  	)
  
  	iov_iter_advance(i, bytes);
  	return true;
  }

  EXPORT_SYMBOL(_copy_from_iter_full);

  size_t _copy_from_iter_nocache(void *addr, size_t bytes, struct iov_iter *i)

  {
  	char *to = addr;

  	if (unlikely(i->type & ITER_PIPE)) {
  		WARN_ON(1);
  		return 0;
  	}

  	iterate_and_advance(i, bytes, v,

  		__copy_from_user_inatomic_nocache((to += v.iov_len) - v.iov_len,

  					 v.iov_base, v.iov_len),
  		memcpy_from_page((to += v.bv_len) - v.bv_len, v.bv_page,
  				 v.bv_offset, v.bv_len),
  		memcpy((to += v.iov_len) - v.iov_len, v.iov_base, v.iov_len)
  	)
  
  	return bytes;
  }

  EXPORT_SYMBOL(_copy_from_iter_nocache);

  #ifdef CONFIG_ARCH_HAS_UACCESS_FLUSHCACHE

  size_t _copy_from_iter_flushcache(void *addr, size_t bytes, struct iov_iter *i)

  {
  	char *to = addr;
  	if (unlikely(i->type & ITER_PIPE)) {
  		WARN_ON(1);
  		return 0;
  	}
  	iterate_and_advance(i, bytes, v,
  		__copy_from_user_flushcache((to += v.iov_len) - v.iov_len,
  					 v.iov_base, v.iov_len),
  		memcpy_page_flushcache((to += v.bv_len) - v.bv_len, v.bv_page,
  				 v.bv_offset, v.bv_len),
  		memcpy_flushcache((to += v.iov_len) - v.iov_len, v.iov_base,
  			v.iov_len)
  	)
  
  	return bytes;
  }

  EXPORT_SYMBOL_GPL(_copy_from_iter_flushcache);

  #endif

  bool _copy_from_iter_full_nocache(void *addr, size_t bytes, struct iov_iter *i)

  {
  	char *to = addr;
  	if (unlikely(i->type & ITER_PIPE)) {
  		WARN_ON(1);
  		return false;
  	}

  	if (unlikely(i->count < bytes))

  		return false;
  	iterate_all_kinds(i, bytes, v, ({

  		if (__copy_from_user_inatomic_nocache((to += v.iov_len) - v.iov_len,

  					     v.iov_base, v.iov_len))
  			return false;
  		0;}),
  		memcpy_from_page((to += v.bv_len) - v.bv_len, v.bv_page,
  				 v.bv_offset, v.bv_len),
  		memcpy((to += v.iov_len) - v.iov_len, v.iov_base, v.iov_len)
  	)
  
  	iov_iter_advance(i, bytes);
  	return true;
  }

  EXPORT_SYMBOL(_copy_from_iter_full_nocache);

  static inline bool page_copy_sane(struct page *page, size_t offset, size_t n)
  {

  	struct page *head = compound_head(page);
  	size_t v = n + offset + page_address(page) - page_address(head);
  
  	if (likely(n <= v && v <= (PAGE_SIZE << compound_order(head))))

  		return true;
  	WARN_ON(1);
  	return false;
  }

  size_t copy_page_to_iter(struct page *page, size_t offset, size_t bytes,
  			 struct iov_iter *i)
  {

  	if (unlikely(!page_copy_sane(page, offset, bytes)))
  		return 0;

  	if (i->type & (ITER_BVEC|ITER_KVEC)) {
  		void *kaddr = kmap_atomic(page);
  		size_t wanted = copy_to_iter(kaddr + offset, bytes, i);
  		kunmap_atomic(kaddr);
  		return wanted;

  	} else if (likely(!(i->type & ITER_PIPE)))

  		return copy_page_to_iter_iovec(page, offset, bytes, i);

  	else
  		return copy_page_to_iter_pipe(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 (unlikely(!page_copy_sane(page, offset, bytes)))
  		return 0;

  	if (unlikely(i->type & ITER_PIPE)) {
  		WARN_ON(1);
  		return 0;
  	}

  	if (i->type & (ITER_BVEC|ITER_KVEC)) {

  		void *kaddr = kmap_atomic(page);

  		size_t wanted = _copy_from_iter(kaddr + offset, bytes, i);

  		kunmap_atomic(kaddr);
  		return wanted;
  	} else

  		return copy_page_from_iter_iovec(page, offset, bytes, i);
  }
  EXPORT_SYMBOL(copy_page_from_iter);

  static size_t pipe_zero(size_t bytes, struct iov_iter *i)
  {
  	struct pipe_inode_info *pipe = i->pipe;
  	size_t n, off;
  	int idx;
  
  	if (!sanity(i))
  		return 0;
  
  	bytes = n = push_pipe(i, bytes, &idx, &off);
  	if (unlikely(!n))
  		return 0;
  
  	for ( ; n; idx = next_idx(idx, pipe), off = 0) {
  		size_t chunk = min_t(size_t, n, PAGE_SIZE - off);
  		memzero_page(pipe->bufs[idx].page, off, chunk);
  		i->idx = idx;
  		i->iov_offset = off + chunk;
  		n -= chunk;
  	}
  	i->count -= bytes;
  	return bytes;
  }

  size_t iov_iter_zero(size_t bytes, struct iov_iter *i)
  {

  	if (unlikely(i->type & ITER_PIPE))
  		return pipe_zero(bytes, i);

  	iterate_and_advance(i, bytes, v,

  		clear_user(v.iov_base, v.iov_len),

  		memzero_page(v.bv_page, v.bv_offset, v.bv_len),
  		memset(v.iov_base, 0, v.iov_len)

  	)
  
  	return bytes;

  }
  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)
  {

  	char *kaddr = kmap_atomic(page), *p = kaddr + offset;

  	if (unlikely(!page_copy_sane(page, offset, bytes))) {
  		kunmap_atomic(kaddr);
  		return 0;
  	}

  	if (unlikely(i->type & ITER_PIPE)) {
  		kunmap_atomic(kaddr);
  		WARN_ON(1);
  		return 0;
  	}

  	iterate_all_kinds(i, bytes, v,

  		copyin((p += v.iov_len) - v.iov_len, v.iov_base, v.iov_len),

  		memcpy_from_page((p += v.bv_len) - v.bv_len, v.bv_page,

  				 v.bv_offset, v.bv_len),
  		memcpy((p += v.iov_len) - v.iov_len, v.iov_base, v.iov_len)

  	)
  	kunmap_atomic(kaddr);
  	return bytes;

  }
  EXPORT_SYMBOL(iov_iter_copy_from_user_atomic);

  static inline void pipe_truncate(struct iov_iter *i)
  {
  	struct pipe_inode_info *pipe = i->pipe;
  	if (pipe->nrbufs) {
  		size_t off = i->iov_offset;
  		int idx = i->idx;
  		int nrbufs = (idx - pipe->curbuf) & (pipe->buffers - 1);
  		if (off) {
  			pipe->bufs[idx].len = off - pipe->bufs[idx].offset;
  			idx = next_idx(idx, pipe);
  			nrbufs++;
  		}
  		while (pipe->nrbufs > nrbufs) {
  			pipe_buf_release(pipe, &pipe->bufs[idx]);
  			idx = next_idx(idx, pipe);
  			pipe->nrbufs--;
  		}
  	}
  }

  static void pipe_advance(struct iov_iter *i, size_t size)
  {
  	struct pipe_inode_info *pipe = i->pipe;

  	if (unlikely(i->count < size))
  		size = i->count;

  	if (size) {

  		struct pipe_buffer *buf;
  		size_t off = i->iov_offset, left = size;
  		int idx = i->idx;

  		if (off) /* make it relative to the beginning of buffer */

  			left += off - pipe->bufs[idx].offset;

  		while (1) {
  			buf = &pipe->bufs[idx];

  			if (left <= buf->len)

  				break;

  			left -= buf->len;

  			idx = next_idx(idx, pipe);
  		}

  		i->idx = idx;

  		i->iov_offset = buf->offset + left;

  	}

  	i->count -= size;
  	/* ... and discard everything past that point */
  	pipe_truncate(i);

  }

  void iov_iter_advance(struct iov_iter *i, size_t size)
  {

  	if (unlikely(i->type & ITER_PIPE)) {
  		pipe_advance(i, size);
  		return;
  	}

  	iterate_and_advance(i, size, v, 0, 0, 0)

  }
  EXPORT_SYMBOL(iov_iter_advance);

  void iov_iter_revert(struct iov_iter *i, size_t unroll)
  {
  	if (!unroll)
  		return;

  	if (WARN_ON(unroll > MAX_RW_COUNT))
  		return;

  	i->count += unroll;
  	if (unlikely(i->type & ITER_PIPE)) {
  		struct pipe_inode_info *pipe = i->pipe;
  		int idx = i->idx;
  		size_t off = i->iov_offset;
  		while (1) {
  			size_t n = off - pipe->bufs[idx].offset;
  			if (unroll < n) {

  				off -= unroll;

  				break;
  			}
  			unroll -= n;
  			if (!unroll && idx == i->start_idx) {
  				off = 0;
  				break;
  			}
  			if (!idx--)
  				idx = pipe->buffers - 1;
  			off = pipe->bufs[idx].offset + pipe->bufs[idx].len;
  		}
  		i->iov_offset = off;
  		i->idx = idx;
  		pipe_truncate(i);
  		return;
  	}
  	if (unroll <= i->iov_offset) {
  		i->iov_offset -= unroll;
  		return;
  	}
  	unroll -= i->iov_offset;
  	if (i->type & ITER_BVEC) {
  		const struct bio_vec *bvec = i->bvec;
  		while (1) {
  			size_t n = (--bvec)->bv_len;
  			i->nr_segs++;
  			if (unroll <= n) {
  				i->bvec = bvec;
  				i->iov_offset = n - unroll;
  				return;
  			}
  			unroll -= n;
  		}
  	} else { /* same logics for iovec and kvec */
  		const struct iovec *iov = i->iov;
  		while (1) {
  			size_t n = (--iov)->iov_len;
  			i->nr_segs++;
  			if (unroll <= n) {
  				i->iov = iov;
  				i->iov_offset = n - unroll;
  				return;
  			}
  			unroll -= n;
  		}
  	}
  }
  EXPORT_SYMBOL(iov_iter_revert);

  /*
   * Return the count of just the current iov_iter segment.
   */
  size_t iov_iter_single_seg_count(const struct iov_iter *i)
  {

  	if (unlikely(i->type & ITER_PIPE))
  		return i->count;	// it is a silly place, anyway

  	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);

  void iov_iter_kvec(struct iov_iter *i, int direction,

  			const struct kvec *kvec, unsigned long nr_segs,

  			size_t count)
  {
  	BUG_ON(!(direction & ITER_KVEC));
  	i->type = direction;

  	i->kvec = kvec;

  	i->nr_segs = nr_segs;
  	i->iov_offset = 0;
  	i->count = count;
  }
  EXPORT_SYMBOL(iov_iter_kvec);

  void iov_iter_bvec(struct iov_iter *i, int direction,
  			const struct bio_vec *bvec, unsigned long nr_segs,
  			size_t count)
  {
  	BUG_ON(!(direction & ITER_BVEC));
  	i->type = direction;
  	i->bvec = bvec;
  	i->nr_segs = nr_segs;
  	i->iov_offset = 0;
  	i->count = count;
  }
  EXPORT_SYMBOL(iov_iter_bvec);

  void iov_iter_pipe(struct iov_iter *i, int direction,
  			struct pipe_inode_info *pipe,
  			size_t count)
  {
  	BUG_ON(direction != ITER_PIPE);

  	WARN_ON(pipe->nrbufs == pipe->buffers);

  	i->type = direction;
  	i->pipe = pipe;
  	i->idx = (pipe->curbuf + pipe->nrbufs) & (pipe->buffers - 1);
  	i->iov_offset = 0;
  	i->count = count;

  	i->start_idx = i->idx;

  }
  EXPORT_SYMBOL(iov_iter_pipe);

  unsigned long iov_iter_alignment(const struct iov_iter *i)
  {

  	unsigned long res = 0;
  	size_t size = i->count;

  	if (unlikely(i->type & ITER_PIPE)) {

  		if (size && i->iov_offset && allocated(&i->pipe->bufs[i->idx]))

  			return size | i->iov_offset;
  		return size;
  	}

  	iterate_all_kinds(i, size, v,
  		(res |= (unsigned long)v.iov_base | v.iov_len, 0),

  		res |= v.bv_offset | v.bv_len,
  		res |= (unsigned long)v.iov_base | v.iov_len

  	)
  	return res;

  }
  EXPORT_SYMBOL(iov_iter_alignment);

  unsigned long iov_iter_gap_alignment(const struct iov_iter *i)
  {

  	unsigned long res = 0;

  	size_t size = i->count;

  	if (unlikely(i->type & ITER_PIPE)) {
  		WARN_ON(1);
  		return ~0U;
  	}

  	iterate_all_kinds(i, size, v,
  		(res |= (!res ? 0 : (unsigned long)v.iov_base) |
  			(size != v.iov_len ? size : 0), 0),
  		(res |= (!res ? 0 : (unsigned long)v.bv_offset) |
  			(size != v.bv_len ? size : 0)),
  		(res |= (!res ? 0 : (unsigned long)v.iov_base) |
  			(size != v.iov_len ? size : 0))
  		);

  	return res;

  }
  EXPORT_SYMBOL(iov_iter_gap_alignment);

  static inline size_t __pipe_get_pages(struct iov_iter *i,
  				size_t maxsize,
  				struct page **pages,
  				int idx,
  				size_t *start)
  {
  	struct pipe_inode_info *pipe = i->pipe;

  	ssize_t n = push_pipe(i, maxsize, &idx, start);

  	if (!n)
  		return -EFAULT;
  
  	maxsize = n;
  	n += *start;

  	while (n > 0) {

  		get_page(*pages++ = pipe->bufs[idx].page);
  		idx = next_idx(idx, pipe);
  		n -= PAGE_SIZE;
  	}
  
  	return maxsize;
  }
  
  static ssize_t pipe_get_pages(struct iov_iter *i,
  		   struct page **pages, size_t maxsize, unsigned maxpages,
  		   size_t *start)
  {
  	unsigned npages;
  	size_t capacity;
  	int idx;

  	if (!maxsize)
  		return 0;

  	if (!sanity(i))
  		return -EFAULT;
  
  	data_start(i, &idx, start);
  	/* some of this one + all after this one */
  	npages = ((i->pipe->curbuf - idx - 1) & (i->pipe->buffers - 1)) + 1;
  	capacity = min(npages,maxpages) * PAGE_SIZE - *start;
  
  	return __pipe_get_pages(i, min(maxsize, capacity), pages, idx, start);
  }

  ssize_t iov_iter_get_pages(struct iov_iter *i,

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

  		   size_t *start)
  {

  	if (maxsize > i->count)
  		maxsize = i->count;

  	if (unlikely(i->type & ITER_PIPE))
  		return pipe_get_pages(i, pages, maxsize, maxpages, start);

  	iterate_all_kinds(i, maxsize, v, ({
  		unsigned long addr = (unsigned long)v.iov_base;
  		size_t len = v.iov_len + (*start = addr & (PAGE_SIZE - 1));
  		int n;
  		int res;
  
  		if (len > maxpages * PAGE_SIZE)
  			len = maxpages * PAGE_SIZE;
  		addr &= ~(PAGE_SIZE - 1);
  		n = DIV_ROUND_UP(len, 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;
  	0;}),({
  		/* can't be more than PAGE_SIZE */
  		*start = v.bv_offset;
  		get_page(*pages = v.bv_page);
  		return v.bv_len;

  	}),({
  		return -EFAULT;

  	})
  	)
  	return 0;

  }
  EXPORT_SYMBOL(iov_iter_get_pages);

  static struct page **get_pages_array(size_t n)
  {

  	return kvmalloc_array(n, sizeof(struct page *), GFP_KERNEL);

  }

  static ssize_t pipe_get_pages_alloc(struct iov_iter *i,
  		   struct page ***pages, size_t maxsize,
  		   size_t *start)
  {
  	struct page **p;
  	size_t n;
  	int idx;
  	int npages;

  	if (!maxsize)
  		return 0;

  	if (!sanity(i))
  		return -EFAULT;
  
  	data_start(i, &idx, start);
  	/* some of this one + all after this one */
  	npages = ((i->pipe->curbuf - idx - 1) & (i->pipe->buffers - 1)) + 1;
  	n = npages * PAGE_SIZE - *start;
  	if (maxsize > n)
  		maxsize = n;
  	else
  		npages = DIV_ROUND_UP(maxsize + *start, PAGE_SIZE);
  	p = get_pages_array(npages);
  	if (!p)
  		return -ENOMEM;
  	n = __pipe_get_pages(i, maxsize, p, idx, start);
  	if (n > 0)
  		*pages = p;
  	else
  		kvfree(p);
  	return n;
  }

  ssize_t iov_iter_get_pages_alloc(struct iov_iter *i,
  		   struct page ***pages, size_t maxsize,
  		   size_t *start)
  {

  	struct page **p;
  
  	if (maxsize > i->count)
  		maxsize = i->count;

  	if (unlikely(i->type & ITER_PIPE))
  		return pipe_get_pages_alloc(i, pages, maxsize, start);

  	iterate_all_kinds(i, maxsize, v, ({
  		unsigned long addr = (unsigned long)v.iov_base;
  		size_t len = v.iov_len + (*start = addr & (PAGE_SIZE - 1));
  		int n;
  		int res;
  
  		addr &= ~(PAGE_SIZE - 1);
  		n = DIV_ROUND_UP(len, PAGE_SIZE);
  		p = get_pages_array(n);
  		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;
  	0;}),({
  		/* can't be more than PAGE_SIZE */
  		*start = v.bv_offset;
  		*pages = p = get_pages_array(1);
  		if (!p)
  			return -ENOMEM;
  		get_page(*p = v.bv_page);
  		return v.bv_len;

  	}),({
  		return -EFAULT;

  	})
  	)
  	return 0;

  }
  EXPORT_SYMBOL(iov_iter_get_pages_alloc);

  size_t csum_and_copy_from_iter(void *addr, size_t bytes, __wsum *csum,
  			       struct iov_iter *i)
  {
  	char *to = addr;
  	__wsum sum, next;
  	size_t off = 0;

  	sum = *csum;

  	if (unlikely(i->type & ITER_PIPE)) {
  		WARN_ON(1);
  		return 0;
  	}

  	iterate_and_advance(i, bytes, v, ({
  		int err = 0;

  		next = csum_and_copy_from_user(v.iov_base,

  					       (to += v.iov_len) - v.iov_len,
  					       v.iov_len, 0, &err);
  		if (!err) {
  			sum = csum_block_add(sum, next, off);
  			off += v.iov_len;
  		}
  		err ? v.iov_len : 0;
  	}), ({
  		char *p = kmap_atomic(v.bv_page);
  		next = csum_partial_copy_nocheck(p + v.bv_offset,
  						 (to += v.bv_len) - v.bv_len,
  						 v.bv_len, 0);
  		kunmap_atomic(p);
  		sum = csum_block_add(sum, next, off);
  		off += v.bv_len;
  	}),({
  		next = csum_partial_copy_nocheck(v.iov_base,
  						 (to += v.iov_len) - v.iov_len,
  						 v.iov_len, 0);
  		sum = csum_block_add(sum, next, off);
  		off += v.iov_len;
  	})
  	)
  	*csum = sum;
  	return bytes;
  }
  EXPORT_SYMBOL(csum_and_copy_from_iter);

  bool csum_and_copy_from_iter_full(void *addr, size_t bytes, __wsum *csum,
  			       struct iov_iter *i)
  {
  	char *to = addr;
  	__wsum sum, next;
  	size_t off = 0;
  	sum = *csum;
  	if (unlikely(i->type & ITER_PIPE)) {
  		WARN_ON(1);
  		return false;
  	}
  	if (unlikely(i->count < bytes))
  		return false;
  	iterate_all_kinds(i, bytes, v, ({
  		int err = 0;
  		next = csum_and_copy_from_user(v.iov_base,
  					       (to += v.iov_len) - v.iov_len,
  					       v.iov_len, 0, &err);
  		if (err)
  			return false;
  		sum = csum_block_add(sum, next, off);
  		off += v.iov_len;
  		0;
  	}), ({
  		char *p = kmap_atomic(v.bv_page);
  		next = csum_partial_copy_nocheck(p + v.bv_offset,
  						 (to += v.bv_len) - v.bv_len,
  						 v.bv_len, 0);
  		kunmap_atomic(p);
  		sum = csum_block_add(sum, next, off);
  		off += v.bv_len;
  	}),({
  		next = csum_partial_copy_nocheck(v.iov_base,
  						 (to += v.iov_len) - v.iov_len,
  						 v.iov_len, 0);
  		sum = csum_block_add(sum, next, off);
  		off += v.iov_len;
  	})
  	)
  	*csum = sum;
  	iov_iter_advance(i, bytes);
  	return true;
  }
  EXPORT_SYMBOL(csum_and_copy_from_iter_full);

  size_t csum_and_copy_to_iter(const void *addr, size_t bytes, __wsum *csum,

  			     struct iov_iter *i)
  {

  	const char *from = addr;

  	__wsum sum, next;
  	size_t off = 0;

  	sum = *csum;

  	if (unlikely(i->type & ITER_PIPE)) {
  		WARN_ON(1);	/* for now */
  		return 0;
  	}

  	iterate_and_advance(i, bytes, v, ({
  		int err = 0;
  		next = csum_and_copy_to_user((from += v.iov_len) - v.iov_len,

  					     v.iov_base,

  					     v.iov_len, 0, &err);
  		if (!err) {
  			sum = csum_block_add(sum, next, off);
  			off += v.iov_len;
  		}
  		err ? v.iov_len : 0;
  	}), ({
  		char *p = kmap_atomic(v.bv_page);
  		next = csum_partial_copy_nocheck((from += v.bv_len) - v.bv_len,
  						 p + v.bv_offset,
  						 v.bv_len, 0);
  		kunmap_atomic(p);
  		sum = csum_block_add(sum, next, off);
  		off += v.bv_len;
  	}),({
  		next = csum_partial_copy_nocheck((from += v.iov_len) - v.iov_len,
  						 v.iov_base,
  						 v.iov_len, 0);
  		sum = csum_block_add(sum, next, off);
  		off += v.iov_len;
  	})
  	)
  	*csum = sum;
  	return bytes;
  }
  EXPORT_SYMBOL(csum_and_copy_to_iter);

  int iov_iter_npages(const struct iov_iter *i, int maxpages)
  {

  	size_t size = i->count;
  	int npages = 0;
  
  	if (!size)
  		return 0;

  	if (unlikely(i->type & ITER_PIPE)) {
  		struct pipe_inode_info *pipe = i->pipe;
  		size_t off;
  		int idx;
  
  		if (!sanity(i))
  			return 0;
  
  		data_start(i, &idx, &off);
  		/* some of this one + all after this one */
  		npages = ((pipe->curbuf - idx - 1) & (pipe->buffers - 1)) + 1;
  		if (npages >= maxpages)
  			return maxpages;
  	} else iterate_all_kinds(i, size, v, ({

  		unsigned long p = (unsigned long)v.iov_base;
  		npages += DIV_ROUND_UP(p + v.iov_len, PAGE_SIZE)
  			- p / PAGE_SIZE;
  		if (npages >= maxpages)
  			return maxpages;
  	0;}),({
  		npages++;
  		if (npages >= maxpages)
  			return maxpages;

  	}),({
  		unsigned long p = (unsigned long)v.iov_base;
  		npages += DIV_ROUND_UP(p + v.iov_len, PAGE_SIZE)
  			- p / PAGE_SIZE;
  		if (npages >= maxpages)
  			return maxpages;

  	})
  	)
  	return npages;

  }

  EXPORT_SYMBOL(iov_iter_npages);

  
  const void *dup_iter(struct iov_iter *new, struct iov_iter *old, gfp_t flags)
  {
  	*new = *old;

  	if (unlikely(new->type & ITER_PIPE)) {
  		WARN_ON(1);
  		return NULL;
  	}

  	if (new->type & ITER_BVEC)
  		return new->bvec = kmemdup(new->bvec,
  				    new->nr_segs * sizeof(struct bio_vec),
  				    flags);
  	else
  		/* iovec and kvec have identical layout */
  		return new->iov = kmemdup(new->iov,
  				   new->nr_segs * sizeof(struct iovec),
  				   flags);
  }
  EXPORT_SYMBOL(dup_iter);

  /**
   * import_iovec() - Copy an array of &struct iovec from userspace
   *     into the kernel, check that it is valid, and initialize a new
   *     &struct iov_iter iterator to access it.
   *
   * @type: One of %READ or %WRITE.
   * @uvector: Pointer to the userspace array.
   * @nr_segs: Number of elements in userspace array.
   * @fast_segs: Number of elements in @iov.
   * @iov: (input and output parameter) Pointer to pointer to (usually small
   *     on-stack) kernel array.
   * @i: Pointer to iterator that will be initialized on success.
   *
   * If the array pointed to by *@iov is large enough to hold all @nr_segs,
   * then this function places %NULL in *@iov on return. Otherwise, a new
   * array will be allocated and the result placed in *@iov. This means that
   * the caller may call kfree() on *@iov regardless of whether the small
   * on-stack array was used or not (and regardless of whether this function
   * returns an error or not).
   *
   * Return: 0 on success or negative error code on error.
   */

  int import_iovec(int type, const struct iovec __user * uvector,
  		 unsigned nr_segs, unsigned fast_segs,
  		 struct iovec **iov, struct iov_iter *i)
  {
  	ssize_t n;
  	struct iovec *p;
  	n = rw_copy_check_uvector(type, uvector, nr_segs, fast_segs,
  				  *iov, &p);
  	if (n < 0) {
  		if (p != *iov)
  			kfree(p);
  		*iov = NULL;
  		return n;
  	}
  	iov_iter_init(i, type, p, nr_segs, n);
  	*iov = p == *iov ? NULL : p;
  	return 0;
  }
  EXPORT_SYMBOL(import_iovec);
  
  #ifdef CONFIG_COMPAT
  #include <linux/compat.h>
  
  int compat_import_iovec(int type, const struct compat_iovec __user * uvector,
  		 unsigned nr_segs, unsigned fast_segs,
  		 struct iovec **iov, struct iov_iter *i)
  {
  	ssize_t n;
  	struct iovec *p;
  	n = compat_rw_copy_check_uvector(type, uvector, nr_segs, fast_segs,
  				  *iov, &p);
  	if (n < 0) {
  		if (p != *iov)
  			kfree(p);
  		*iov = NULL;
  		return n;
  	}
  	iov_iter_init(i, type, p, nr_segs, n);
  	*iov = p == *iov ? NULL : p;
  	return 0;
  }
  #endif
  
  int import_single_range(int rw, void __user *buf, size_t len,
  		 struct iovec *iov, struct iov_iter *i)
  {
  	if (len > MAX_RW_COUNT)
  		len = MAX_RW_COUNT;
  	if (unlikely(!access_ok(!rw, buf, len)))
  		return -EFAULT;
  
  	iov->iov_base = buf;
  	iov->iov_len = len;
  	iov_iter_init(i, rw, iov, 1, len);
  	return 0;
  }

  EXPORT_SYMBOL(import_single_range);