include/linux/uio.h - linux - Git at Google

 /* SPDX-License-Identifier: GPL-2.0-or-later */
 /*
  *	Berkeley style UIO structures	-	Alan Cox 1994.
  */
 #ifndef __LINUX_UIO_H
 #define __LINUX_UIO_H

 #include <linux/kernel.h>
 #include <linux/thread_info.h>
 #include <linux/mm_types.h>
 #include <uapi/linux/uio.h>

 struct page;
 struct folio_queue;

 typedef unsigned int __bitwise iov_iter_extraction_t;

 struct kvec {
 	void *iov_base; /* and that should *never* hold a userland pointer */
 	size_t iov_len;
 };

 enum iter_type {
 	/* iter types */
 	ITER_UBUF,
 	ITER_IOVEC,
 	ITER_BVEC,
 	ITER_KVEC,
 	ITER_FOLIOQ,
 	ITER_XARRAY,
 	ITER_DISCARD,
 };

 #define ITER_SOURCE	1	// == WRITE
 #define ITER_DEST	0	// == READ

 struct iov_iter_state {
 	size_t iov_offset;
 	size_t count;
 	unsigned long nr_segs;
 };

 struct iov_iter {
 	u8 iter_type;
 	bool nofault;
 	bool data_source;
 	size_t iov_offset;
 	/*
 	 * Hack alert: overlay ubuf_iovec with iovec + count, so
 	 * that the members resolve correctly regardless of the type
 	 * of iterator used. This means that you can use:
 	 *
 	 * &iter->__ubuf_iovec or iter->__iov
 	 *
 	 * interchangably for the user_backed cases, hence simplifying
 	 * some of the cases that need to deal with both.
 	 */
 	union {
 		/*
 		 * This really should be a const, but we cannot do that without
 		 * also modifying any of the zero-filling iter init functions.
 		 * Leave it non-const for now, but it should be treated as such.
 		 */
 		struct iovec __ubuf_iovec;
 		struct {
 			union {
 				/* use iter_iov() to get the current vec */
 				const struct iovec *__iov;
 				const struct kvec *kvec;
 				const struct bio_vec *bvec;
 				const struct folio_queue *folioq;
 				struct xarray *xarray;
 				void __user *ubuf;
 			};
 			size_t count;
 		};
 	};
 	union {
 		unsigned long nr_segs;
 		u8 folioq_slot;
 		loff_t xarray_start;
 	};
 };

 static inline const struct iovec *iter_iov(const struct iov_iter *iter)
 {
 	if (iter->iter_type == ITER_UBUF)
 		return (const struct iovec *) &iter->__ubuf_iovec;
 	return iter->__iov;
 }

 #define iter_iov_addr(iter)	(iter_iov(iter)->iov_base + (iter)->iov_offset)
 #define iter_iov_len(iter)	(iter_iov(iter)->iov_len - (iter)->iov_offset)

 static inline enum iter_type iov_iter_type(const struct iov_iter *i)
 {
 	return i->iter_type;
 }

 static inline void iov_iter_save_state(struct iov_iter *iter,
 				       struct iov_iter_state *state)
 {
 	state->iov_offset = iter->iov_offset;
 	state->count = iter->count;
 	state->nr_segs = iter->nr_segs;
 }

 static inline bool iter_is_ubuf(const struct iov_iter *i)
 {
 	return iov_iter_type(i) == ITER_UBUF;
 }

 static inline bool iter_is_iovec(const struct iov_iter *i)
 {
 	return iov_iter_type(i) == ITER_IOVEC;
 }

 static inline bool iov_iter_is_kvec(const struct iov_iter *i)
 {
 	return iov_iter_type(i) == ITER_KVEC;
 }

 static inline bool iov_iter_is_bvec(const struct iov_iter *i)
 {
 	return iov_iter_type(i) == ITER_BVEC;
 }

 static inline bool iov_iter_is_discard(const struct iov_iter *i)
 {
 	return iov_iter_type(i) == ITER_DISCARD;
 }

 static inline bool iov_iter_is_folioq(const struct iov_iter *i)
 {
 	return iov_iter_type(i) == ITER_FOLIOQ;
 }

 static inline bool iov_iter_is_xarray(const struct iov_iter *i)
 {
 	return iov_iter_type(i) == ITER_XARRAY;
 }

 static inline unsigned char iov_iter_rw(const struct iov_iter *i)
 {
 	return i->data_source ? WRITE : READ;
 }

 static inline bool user_backed_iter(const struct iov_iter *i)
 {
 	return iter_is_ubuf(i) || iter_is_iovec(i);
 }

 /*
  * Total number of bytes covered by an iovec.
  *
  * NOTE that it is not safe to use this function until all the iovec's
  * segment lengths have been validated.  Because the individual lengths can
  * overflow a size_t when added together.
  */
 static inline size_t iov_length(const struct iovec *iov, unsigned long nr_segs)
 {
 	unsigned long seg;
 	size_t ret = 0;

 	for (seg = 0; seg < nr_segs; seg++)
 		ret += iov[seg].iov_len;
 	return ret;
 }

 size_t copy_page_from_iter_atomic(struct page *page, size_t offset,
 				  size_t bytes, struct iov_iter *i);
 void iov_iter_advance(struct iov_iter *i, size_t bytes);
 void iov_iter_revert(struct iov_iter *i, size_t bytes);
 size_t fault_in_iov_iter_readable(const struct iov_iter *i, size_t bytes);
 size_t fault_in_iov_iter_writeable(const struct iov_iter *i, size_t bytes);
 size_t iov_iter_single_seg_count(const struct iov_iter *i);
 size_t copy_page_to_iter(struct page *page, size_t offset, size_t bytes,
 			 struct iov_iter *i);
 size_t copy_page_from_iter(struct page *page, size_t offset, size_t bytes,
 			 struct iov_iter *i);

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

 static inline size_t copy_folio_to_iter(struct folio *folio, size_t offset,
 		size_t bytes, struct iov_iter *i)
 {
 	return copy_page_to_iter(&folio->page, offset, bytes, i);
 }

 static inline size_t copy_folio_from_iter(struct folio *folio, size_t offset,
 					  size_t bytes, struct iov_iter *i)
 {
 	return copy_page_from_iter(&folio->page, offset, bytes, i);
 }

 static inline size_t copy_folio_from_iter_atomic(struct folio *folio,
 		size_t offset, size_t bytes, struct iov_iter *i)
 {
 	return copy_page_from_iter_atomic(&folio->page, offset, bytes, i);
 }

 size_t copy_page_to_iter_nofault(struct page *page, unsigned offset,
 				 size_t bytes, struct iov_iter *i);

 static __always_inline __must_check
 size_t copy_to_iter(const void *addr, size_t bytes, struct iov_iter *i)
 {
 	if (check_copy_size(addr, bytes, true))
 		return _copy_to_iter(addr, bytes, i);
 	return 0;
 }

 static __always_inline __must_check
 size_t copy_from_iter(void *addr, size_t bytes, struct iov_iter *i)
 {
 	if (check_copy_size(addr, bytes, false))
 		return _copy_from_iter(addr, bytes, i);
 	return 0;
 }

 static __always_inline __must_check
 bool copy_to_iter_full(const void *addr, size_t bytes, struct iov_iter *i)
 {
 	size_t copied = copy_to_iter(addr, bytes, i);
 	if (likely(copied == bytes))
 		return true;
 	iov_iter_revert(i, copied);
 	return false;
 }

 static __always_inline __must_check
 bool copy_from_iter_full(void *addr, size_t bytes, struct iov_iter *i)
 {
 	size_t copied = copy_from_iter(addr, bytes, i);
 	if (likely(copied == bytes))
 		return true;
 	iov_iter_revert(i, copied);
 	return false;
 }

 static __always_inline __must_check
 size_t copy_from_iter_nocache(void *addr, size_t bytes, struct iov_iter *i)
 {
 	if (check_copy_size(addr, bytes, false))
 		return _copy_from_iter_nocache(addr, bytes, i);
 	return 0;
 }

 static __always_inline __must_check
 bool copy_from_iter_full_nocache(void *addr, size_t bytes, struct iov_iter *i)
 {
 	size_t copied = copy_from_iter_nocache(addr, bytes, i);
 	if (likely(copied == bytes))
 		return true;
 	iov_iter_revert(i, copied);
 	return false;
 }

 #ifdef CONFIG_ARCH_HAS_UACCESS_FLUSHCACHE
 /*
  * Note, users like pmem that depend on the stricter semantics of
  * _copy_from_iter_flushcache() than _copy_from_iter_nocache() must check for
  * IS_ENABLED(CONFIG_ARCH_HAS_UACCESS_FLUSHCACHE) before assuming that the
  * destination is flushed from the cache on return.
  */
 size_t _copy_from_iter_flushcache(void *addr, size_t bytes, struct iov_iter *i);
 #else
 #define _copy_from_iter_flushcache _copy_from_iter_nocache
 #endif

 #ifdef CONFIG_ARCH_HAS_COPY_MC
 size_t _copy_mc_to_iter(const void *addr, size_t bytes, struct iov_iter *i);
 #else
 #define _copy_mc_to_iter _copy_to_iter
 #endif

 size_t iov_iter_zero(size_t bytes, struct iov_iter *);
 bool iov_iter_is_aligned(const struct iov_iter *i, unsigned addr_mask,
 			unsigned len_mask);
 unsigned long iov_iter_alignment(const struct iov_iter *i);
 unsigned long iov_iter_gap_alignment(const struct iov_iter *i);
 void iov_iter_init(struct iov_iter *i, unsigned int direction, const struct iovec *iov,
 			unsigned long nr_segs, size_t count);
 void iov_iter_kvec(struct iov_iter *i, unsigned int direction, const struct kvec *kvec,
 			unsigned long nr_segs, size_t count);
 void iov_iter_bvec(struct iov_iter *i, unsigned int direction, const struct bio_vec *bvec,
 			unsigned long nr_segs, size_t count);
 void iov_iter_discard(struct iov_iter *i, unsigned int direction, size_t count);
 void iov_iter_folio_queue(struct iov_iter *i, unsigned int direction,
 			  const struct folio_queue *folioq,
 			  unsigned int first_slot, unsigned int offset, size_t count);
 void iov_iter_xarray(struct iov_iter *i, unsigned int direction, struct xarray *xarray,
 		     loff_t start, size_t count);
 ssize_t iov_iter_get_pages2(struct iov_iter *i, struct page **pages,
 			size_t maxsize, unsigned maxpages, size_t *start);
 ssize_t iov_iter_get_pages_alloc2(struct iov_iter *i, struct page ***pages,
 			size_t maxsize, size_t *start);
 int iov_iter_npages(const struct iov_iter *i, int maxpages);
 void iov_iter_restore(struct iov_iter *i, struct iov_iter_state *state);

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

 static inline size_t iov_iter_count(const struct iov_iter *i)
 {
 	return i->count;
 }

 /*
  * Cap the iov_iter by given limit; note that the second argument is
  * *not* the new size - it's upper limit for such.  Passing it a value
  * greater than the amount of data in iov_iter is fine - it'll just do
  * nothing in that case.
  */
 static inline void iov_iter_truncate(struct iov_iter *i, u64 count)
 {
 	/*
 	 * count doesn't have to fit in size_t - comparison extends both
 	 * operands to u64 here and any value that would be truncated by
 	 * conversion in assignement is by definition greater than all
 	 * values of size_t, including old i->count.
 	 */
 	if (i->count > count)
 		i->count = count;
 }

 /*
  * reexpand a previously truncated iterator; count must be no more than how much
  * we had shrunk it.
  */
 static inline void iov_iter_reexpand(struct iov_iter *i, size_t count)
 {
 	i->count = count;
 }

 static inline int
 iov_iter_npages_cap(struct iov_iter *i, int maxpages, size_t max_bytes)
 {
 	size_t shorted = 0;
 	int npages;

 	if (iov_iter_count(i) > max_bytes) {
 		shorted = iov_iter_count(i) - max_bytes;
 		iov_iter_truncate(i, max_bytes);
 	}
 	npages = iov_iter_npages(i, maxpages);
 	if (shorted)
 		iov_iter_reexpand(i, iov_iter_count(i) + shorted);

 	return npages;
 }

 struct iovec *iovec_from_user(const struct iovec __user *uvector,
 		unsigned long nr_segs, unsigned long fast_segs,
 		struct iovec *fast_iov, bool compat);
 ssize_t import_iovec(int type, const struct iovec __user *uvec,
 		 unsigned nr_segs, unsigned fast_segs, struct iovec **iovp,
 		 struct iov_iter *i);
 ssize_t __import_iovec(int type, const struct iovec __user *uvec,
 		 unsigned nr_segs, unsigned fast_segs, struct iovec **iovp,
 		 struct iov_iter *i, bool compat);
 int import_ubuf(int type, void __user *buf, size_t len, struct iov_iter *i);

 static inline void iov_iter_ubuf(struct iov_iter *i, unsigned int direction,
 			void __user *buf, size_t count)
 {
 	WARN_ON(direction & ~(READ | WRITE));
 	*i = (struct iov_iter) {
 		.iter_type = ITER_UBUF,
 		.data_source = direction,
 		.ubuf = buf,
 		.count = count,
 		.nr_segs = 1
 	};
 }
 /* Flags for iov_iter_get/extract_pages*() */
 /* Allow P2PDMA on the extracted pages */
 #define ITER_ALLOW_P2PDMA	((__force iov_iter_extraction_t)0x01)

 ssize_t iov_iter_extract_pages(struct iov_iter *i, struct page ***pages,
 			       size_t maxsize, unsigned int maxpages,
 			       iov_iter_extraction_t extraction_flags,
 			       size_t *offset0);

 /**
  * iov_iter_extract_will_pin - Indicate how pages from the iterator will be retained
  * @iter: The iterator
  *
  * Examine the iterator and indicate by returning true or false as to how, if
  * at all, pages extracted from the iterator will be retained by the extraction
  * function.
  *
  * %true indicates that the pages will have a pin placed in them that the
  * caller must unpin.  This is must be done for DMA/async DIO to force fork()
  * to forcibly copy a page for the child (the parent must retain the original
  * page).
  *
  * %false indicates that no measures are taken and that it's up to the caller
  * to retain the pages.
  */
 static inline bool iov_iter_extract_will_pin(const struct iov_iter *iter)
 {
 	return user_backed_iter(iter);
 }

 struct sg_table;
 ssize_t extract_iter_to_sg(struct iov_iter *iter, size_t len,
 			   struct sg_table *sgtable, unsigned int sg_max,
 			   iov_iter_extraction_t extraction_flags);

 #endif
	/* SPDX-License-Identifier: GPL-2.0-or-later */
	/*
	* Berkeley style UIO structures - Alan Cox 1994.
	*/
	#ifndef __LINUX_UIO_H
	#define __LINUX_UIO_H

	#include <linux/kernel.h>
	#include <linux/thread_info.h>
	#include <linux/mm_types.h>
	#include <uapi/linux/uio.h>

	struct page;
	struct folio_queue;

	typedef unsigned int __bitwise iov_iter_extraction_t;

	struct kvec {
	void iov_base; / and that should never hold a userland pointer */
	size_t iov_len;
	};

	enum iter_type {
	/* iter types */
	ITER_UBUF,
	ITER_IOVEC,
	ITER_BVEC,
	ITER_KVEC,
	ITER_FOLIOQ,
	ITER_XARRAY,
	ITER_DISCARD,
	};

	#define ITER_SOURCE 1 // == WRITE
	#define ITER_DEST 0 // == READ

	struct iov_iter_state {
	size_t iov_offset;
	size_t count;
	unsigned long nr_segs;
	};

	struct iov_iter {
	u8 iter_type;
	bool nofault;
	bool data_source;
	size_t iov_offset;
	/*
	* Hack alert: overlay ubuf_iovec with iovec + count, so
	* that the members resolve correctly regardless of the type
	* of iterator used. This means that you can use:
	*
	* &iter->__ubuf_iovec or iter->__iov
	*
	* interchangably for the user_backed cases, hence simplifying
	* some of the cases that need to deal with both.
	*/
	union {
	/*
	* This really should be a const, but we cannot do that without
	* also modifying any of the zero-filling iter init functions.
	* Leave it non-const for now, but it should be treated as such.
	*/
	struct iovec __ubuf_iovec;
	struct {
	union {
	/* use iter_iov() to get the current vec */
	const struct iovec *__iov;
	const struct kvec *kvec;
	const struct bio_vec *bvec;
	const struct folio_queue *folioq;
	struct xarray *xarray;
	void __user *ubuf;
	};
	size_t count;
	};
	};
	union {
	unsigned long nr_segs;
	u8 folioq_slot;
	loff_t xarray_start;
	};
	};

	static inline const struct iovec iter_iov(const struct iov_iter iter)
	{
	if (iter->iter_type == ITER_UBUF)
	return (const struct iovec *) &iter->__ubuf_iovec;
	return iter->__iov;
	}

	#define iter_iov_addr(iter) (iter_iov(iter)->iov_base + (iter)->iov_offset)
	#define iter_iov_len(iter) (iter_iov(iter)->iov_len - (iter)->iov_offset)

	static inline enum iter_type iov_iter_type(const struct iov_iter *i)
	{
	return i->iter_type;
	}

	static inline void iov_iter_save_state(struct iov_iter *iter,
	struct iov_iter_state *state)
	{
	state->iov_offset = iter->iov_offset;
	state->count = iter->count;
	state->nr_segs = iter->nr_segs;
	}

	static inline bool iter_is_ubuf(const struct iov_iter *i)
	{
	return iov_iter_type(i) == ITER_UBUF;
	}

	static inline bool iter_is_iovec(const struct iov_iter *i)
	{
	return iov_iter_type(i) == ITER_IOVEC;
	}

	static inline bool iov_iter_is_kvec(const struct iov_iter *i)
	{
	return iov_iter_type(i) == ITER_KVEC;
	}

	static inline bool iov_iter_is_bvec(const struct iov_iter *i)
	{
	return iov_iter_type(i) == ITER_BVEC;
	}

	static inline bool iov_iter_is_discard(const struct iov_iter *i)
	{
	return iov_iter_type(i) == ITER_DISCARD;
	}

	static inline bool iov_iter_is_folioq(const struct iov_iter *i)
	{
	return iov_iter_type(i) == ITER_FOLIOQ;
	}

	static inline bool iov_iter_is_xarray(const struct iov_iter *i)
	{
	return iov_iter_type(i) == ITER_XARRAY;
	}

	static inline unsigned char iov_iter_rw(const struct iov_iter *i)
	{
	return i->data_source ? WRITE : READ;
	}

	static inline bool user_backed_iter(const struct iov_iter *i)
	{
	return iter_is_ubuf(i) \|\| iter_is_iovec(i);
	}

	/*
	* Total number of bytes covered by an iovec.
	*
	* NOTE that it is not safe to use this function until all the iovec's
	* segment lengths have been validated. Because the individual lengths can
	* overflow a size_t when added together.
	*/
	static inline size_t iov_length(const struct iovec *iov, unsigned long nr_segs)
	{
	unsigned long seg;
	size_t ret = 0;

	for (seg = 0; seg < nr_segs; seg++)
	ret += iov[seg].iov_len;
	return ret;
	}

	size_t copy_page_from_iter_atomic(struct page *page, size_t offset,
	size_t bytes, struct iov_iter *i);
	void iov_iter_advance(struct iov_iter *i, size_t bytes);
	void iov_iter_revert(struct iov_iter *i, size_t bytes);
	size_t fault_in_iov_iter_readable(const struct iov_iter *i, size_t bytes);
	size_t fault_in_iov_iter_writeable(const struct iov_iter *i, size_t bytes);
	size_t iov_iter_single_seg_count(const struct iov_iter *i);
	size_t copy_page_to_iter(struct page *page, size_t offset, size_t bytes,
	struct iov_iter *i);
	size_t copy_page_from_iter(struct page *page, size_t offset, size_t bytes,
	struct iov_iter *i);

	size_t _copy_to_iter(const void addr, size_t bytes, struct iov_iter i);
	size_t _copy_from_iter(void addr, size_t bytes, struct iov_iter i);
	size_t _copy_from_iter_nocache(void addr, size_t bytes, struct iov_iter i);

	static inline size_t copy_folio_to_iter(struct folio *folio, size_t offset,
	size_t bytes, struct iov_iter *i)
	{
	return copy_page_to_iter(&folio->page, offset, bytes, i);
	}

	static inline size_t copy_folio_from_iter(struct folio *folio, size_t offset,
	size_t bytes, struct iov_iter *i)
	{
	return copy_page_from_iter(&folio->page, offset, bytes, i);
	}

	static inline size_t copy_folio_from_iter_atomic(struct folio *folio,
	size_t offset, size_t bytes, struct iov_iter *i)
	{
	return copy_page_from_iter_atomic(&folio->page, offset, bytes, i);
	}

	size_t copy_page_to_iter_nofault(struct page *page, unsigned offset,
	size_t bytes, struct iov_iter *i);

	static __always_inline __must_check
	size_t copy_to_iter(const void addr, size_t bytes, struct iov_iter i)
	{
	if (check_copy_size(addr, bytes, true))
	return _copy_to_iter(addr, bytes, i);
	return 0;
	}

	static __always_inline __must_check
	size_t copy_from_iter(void addr, size_t bytes, struct iov_iter i)
	{
	if (check_copy_size(addr, bytes, false))
	return _copy_from_iter(addr, bytes, i);
	return 0;
	}

	static __always_inline __must_check
	bool copy_to_iter_full(const void addr, size_t bytes, struct iov_iter i)
	{
	size_t copied = copy_to_iter(addr, bytes, i);
	if (likely(copied == bytes))
	return true;
	iov_iter_revert(i, copied);
	return false;
	}

	static __always_inline __must_check
	bool copy_from_iter_full(void addr, size_t bytes, struct iov_iter i)
	{
	size_t copied = copy_from_iter(addr, bytes, i);
	if (likely(copied == bytes))
	return true;
	iov_iter_revert(i, copied);
	return false;
	}

	static __always_inline __must_check
	size_t copy_from_iter_nocache(void addr, size_t bytes, struct iov_iter i)
	{
	if (check_copy_size(addr, bytes, false))
	return _copy_from_iter_nocache(addr, bytes, i);
	return 0;
	}

	static __always_inline __must_check
	bool copy_from_iter_full_nocache(void addr, size_t bytes, struct iov_iter i)
	{
	size_t copied = copy_from_iter_nocache(addr, bytes, i);
	if (likely(copied == bytes))
	return true;
	iov_iter_revert(i, copied);
	return false;
	}

	#ifdef CONFIG_ARCH_HAS_UACCESS_FLUSHCACHE
	/*
	* Note, users like pmem that depend on the stricter semantics of
	* _copy_from_iter_flushcache() than _copy_from_iter_nocache() must check for
	* IS_ENABLED(CONFIG_ARCH_HAS_UACCESS_FLUSHCACHE) before assuming that the
	* destination is flushed from the cache on return.
	*/
	size_t _copy_from_iter_flushcache(void addr, size_t bytes, struct iov_iter i);
	#else
	#define _copy_from_iter_flushcache _copy_from_iter_nocache
	#endif

	#ifdef CONFIG_ARCH_HAS_COPY_MC
	size_t _copy_mc_to_iter(const void addr, size_t bytes, struct iov_iter i);
	#else
	#define _copy_mc_to_iter _copy_to_iter
	#endif

	size_t iov_iter_zero(size_t bytes, struct iov_iter *);
	bool iov_iter_is_aligned(const struct iov_iter *i, unsigned addr_mask,
	unsigned len_mask);
	unsigned long iov_iter_alignment(const struct iov_iter *i);
	unsigned long iov_iter_gap_alignment(const struct iov_iter *i);
	void iov_iter_init(struct iov_iter i, unsigned int direction, const struct iovec iov,
	unsigned long nr_segs, size_t count);
	void iov_iter_kvec(struct iov_iter i, unsigned int direction, const struct kvec kvec,
	unsigned long nr_segs, size_t count);
	void iov_iter_bvec(struct iov_iter i, unsigned int direction, const struct bio_vec bvec,
	unsigned long nr_segs, size_t count);
	void iov_iter_discard(struct iov_iter *i, unsigned int direction, size_t count);
	void iov_iter_folio_queue(struct iov_iter *i, unsigned int direction,
	const struct folio_queue *folioq,
	unsigned int first_slot, unsigned int offset, size_t count);
	void iov_iter_xarray(struct iov_iter i, unsigned int direction, struct xarray xarray,
	loff_t start, size_t count);
	ssize_t iov_iter_get_pages2(struct iov_iter i, struct page *pages,
	size_t maxsize, unsigned maxpages, size_t *start);
	ssize_t iov_iter_get_pages_alloc2(struct iov_iter i, struct page **pages,
	size_t maxsize, size_t *start);
	int iov_iter_npages(const struct iov_iter *i, int maxpages);
	void iov_iter_restore(struct iov_iter i, struct iov_iter_state state);

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

	static inline size_t iov_iter_count(const struct iov_iter *i)
	{
	return i->count;
	}

	/*
	* Cap the iov_iter by given limit; note that the second argument is
	* not the new size - it's upper limit for such. Passing it a value
	* greater than the amount of data in iov_iter is fine - it'll just do
	* nothing in that case.
	*/
	static inline void iov_iter_truncate(struct iov_iter *i, u64 count)
	{
	/*
	* count doesn't have to fit in size_t - comparison extends both
	* operands to u64 here and any value that would be truncated by
	* conversion in assignement is by definition greater than all
	* values of size_t, including old i->count.
	*/
	if (i->count > count)
	i->count = count;
	}

	/*
	* reexpand a previously truncated iterator; count must be no more than how much
	* we had shrunk it.
	*/
	static inline void iov_iter_reexpand(struct iov_iter *i, size_t count)
	{
	i->count = count;
	}

	static inline int
	iov_iter_npages_cap(struct iov_iter *i, int maxpages, size_t max_bytes)
	{
	size_t shorted = 0;
	int npages;

	if (iov_iter_count(i) > max_bytes) {
	shorted = iov_iter_count(i) - max_bytes;
	iov_iter_truncate(i, max_bytes);
	}
	npages = iov_iter_npages(i, maxpages);
	if (shorted)
	iov_iter_reexpand(i, iov_iter_count(i) + shorted);

	return npages;
	}

	struct iovec iovec_from_user(const struct iovec __user uvector,
	unsigned long nr_segs, unsigned long fast_segs,
	struct iovec *fast_iov, bool compat);
	ssize_t import_iovec(int type, const struct iovec __user *uvec,
	unsigned nr_segs, unsigned fast_segs, struct iovec **iovp,
	struct iov_iter *i);
	ssize_t __import_iovec(int type, const struct iovec __user *uvec,
	unsigned nr_segs, unsigned fast_segs, struct iovec **iovp,
	struct iov_iter *i, bool compat);
	int import_ubuf(int type, void __user buf, size_t len, struct iov_iter i);

	static inline void iov_iter_ubuf(struct iov_iter *i, unsigned int direction,
	void __user *buf, size_t count)
	{
	WARN_ON(direction & ~(READ \| WRITE));
	*i = (struct iov_iter) {
	.iter_type = ITER_UBUF,
	.data_source = direction,
	.ubuf = buf,
	.count = count,
	.nr_segs = 1
	};
	}
	/* Flags for iov_iter_get/extract_pages() /
	/* Allow P2PDMA on the extracted pages */
	#define ITER_ALLOW_P2PDMA ((__force iov_iter_extraction_t)0x01)

	ssize_t iov_iter_extract_pages(struct iov_iter i, struct page **pages,
	size_t maxsize, unsigned int maxpages,
	iov_iter_extraction_t extraction_flags,
	size_t *offset0);

	/**
	* iov_iter_extract_will_pin - Indicate how pages from the iterator will be retained
	* @iter: The iterator
	*
	* Examine the iterator and indicate by returning true or false as to how, if
	* at all, pages extracted from the iterator will be retained by the extraction
	* function.
	*
	* %true indicates that the pages will have a pin placed in them that the
	* caller must unpin. This is must be done for DMA/async DIO to force fork()
	* to forcibly copy a page for the child (the parent must retain the original
	* page).
	*
	* %false indicates that no measures are taken and that it's up to the caller
	* to retain the pages.
	*/
	static inline bool iov_iter_extract_will_pin(const struct iov_iter *iter)
	{
	return user_backed_iter(iter);
	}

	struct sg_table;
	ssize_t extract_iter_to_sg(struct iov_iter *iter, size_t len,
	struct sg_table *sgtable, unsigned int sg_max,
	iov_iter_extraction_t extraction_flags);

	#endif