include/linux/iov_iter.h - kernel/common - Git at Google

 /* SPDX-License-Identifier: GPL-2.0-or-later */
 /* I/O iterator iteration building functions.
  *
  * Copyright (C) 2023 Red Hat, Inc. All Rights Reserved.
  * Written by David Howells (dhowells@redhat.com)
  */

 #ifndef _LINUX_IOV_ITER_H
 #define _LINUX_IOV_ITER_H

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

 typedef size_t (*iov_step_f)(void *iter_base, size_t progress, size_t len,
 			     void *priv, void *priv2);
 typedef size_t (*iov_ustep_f)(void __user *iter_base, size_t progress, size_t len,
 			      void *priv, void *priv2);

 /*
  * Handle ITER_UBUF.
  */
 static __always_inline
 size_t iterate_ubuf(struct iov_iter *iter, size_t len, void *priv, void *priv2,
 		    iov_ustep_f step)
 {
 	void __user *base = iter->ubuf;
 	size_t progress = 0, remain;

 	remain = step(base + iter->iov_offset, 0, len, priv, priv2);
 	progress = len - remain;
 	iter->iov_offset += progress;
 	iter->count -= progress;
 	return progress;
 }

 /*
  * Handle ITER_IOVEC.
  */
 static __always_inline
 size_t iterate_iovec(struct iov_iter *iter, size_t len, void *priv, void *priv2,
 		     iov_ustep_f step)
 {
 	const struct iovec *p = iter->__iov;
 	size_t progress = 0, skip = iter->iov_offset;

 	do {
 		size_t remain, consumed;
 		size_t part = min(len, p->iov_len - skip);

 		if (likely(part)) {
 			remain = step(p->iov_base + skip, progress, part, priv, priv2);
 			consumed = part - remain;
 			progress += consumed;
 			skip += consumed;
 			len -= consumed;
 			if (skip < p->iov_len)
 				break;
 		}
 		p++;
 		skip = 0;
 	} while (len);

 	iter->nr_segs -= p - iter->__iov;
 	iter->__iov = p;
 	iter->iov_offset = skip;
 	iter->count -= progress;
 	return progress;
 }

 /*
  * Handle ITER_KVEC.
  */
 static __always_inline
 size_t iterate_kvec(struct iov_iter *iter, size_t len, void *priv, void *priv2,
 		    iov_step_f step)
 {
 	const struct kvec *p = iter->kvec;
 	size_t progress = 0, skip = iter->iov_offset;

 	do {
 		size_t remain, consumed;
 		size_t part = min(len, p->iov_len - skip);

 		if (likely(part)) {
 			remain = step(p->iov_base + skip, progress, part, priv, priv2);
 			consumed = part - remain;
 			progress += consumed;
 			skip += consumed;
 			len -= consumed;
 			if (skip < p->iov_len)
 				break;
 		}
 		p++;
 		skip = 0;
 	} while (len);

 	iter->nr_segs -= p - iter->kvec;
 	iter->kvec = p;
 	iter->iov_offset = skip;
 	iter->count -= progress;
 	return progress;
 }

 /*
  * Handle ITER_BVEC.
  */
 static __always_inline
 size_t iterate_bvec(struct iov_iter *iter, size_t len, void *priv, void *priv2,
 		    iov_step_f step)
 {
 	const struct bio_vec *p = iter->bvec;
 	size_t progress = 0, skip = iter->iov_offset;

 	do {
 		size_t remain, consumed;
 		size_t offset = p->bv_offset + skip, part;
 		void *kaddr = kmap_local_page(p->bv_page + offset / PAGE_SIZE);

 		part = min3(len,
 			   (size_t)(p->bv_len - skip),
 			   (size_t)(PAGE_SIZE - offset % PAGE_SIZE));
 		remain = step(kaddr + offset % PAGE_SIZE, progress, part, priv, priv2);
 		kunmap_local(kaddr);
 		consumed = part - remain;
 		len -= consumed;
 		progress += consumed;
 		skip += consumed;
 		if (skip >= p->bv_len) {
 			skip = 0;
 			p++;
 		}
 		if (remain)
 			break;
 	} while (len);

 	iter->nr_segs -= p - iter->bvec;
 	iter->bvec = p;
 	iter->iov_offset = skip;
 	iter->count -= progress;
 	return progress;
 }

 /*
  * Handle ITER_XARRAY.
  */
 static __always_inline
 size_t iterate_xarray(struct iov_iter *iter, size_t len, void *priv, void *priv2,
 		      iov_step_f step)
 {
 	struct folio *folio;
 	size_t progress = 0;
 	loff_t start = iter->xarray_start + iter->iov_offset;
 	pgoff_t index = start / PAGE_SIZE;
 	XA_STATE(xas, iter->xarray, index);

 	rcu_read_lock();
 	xas_for_each(&xas, folio, ULONG_MAX) {
 		size_t remain, consumed, offset, part, flen;

 		if (xas_retry(&xas, folio))
 			continue;
 		if (WARN_ON(xa_is_value(folio)))
 			break;
 		if (WARN_ON(folio_test_hugetlb(folio)))
 			break;

 		offset = offset_in_folio(folio, start + progress);
 		flen = min(folio_size(folio) - offset, len);

 		while (flen) {
 			void *base = kmap_local_folio(folio, offset);

 			part = min_t(size_t, flen,
 				     PAGE_SIZE - offset_in_page(offset));
 			remain = step(base, progress, part, priv, priv2);
 			kunmap_local(base);

 			consumed = part - remain;
 			progress += consumed;
 			len -= consumed;

 			if (remain || len == 0)
 				goto out;
 			flen -= consumed;
 			offset += consumed;
 		}
 	}

 out:
 	rcu_read_unlock();
 	iter->iov_offset += progress;
 	iter->count -= progress;
 	return progress;
 }

 /*
  * Handle ITER_DISCARD.
  */
 static __always_inline
 size_t iterate_discard(struct iov_iter *iter, size_t len, void *priv, void *priv2,
 		      iov_step_f step)
 {
 	size_t progress = len;

 	iter->count -= progress;
 	return progress;
 }

 /**
  * iterate_and_advance2 - Iterate over an iterator
  * @iter: The iterator to iterate over.
  * @len: The amount to iterate over.
  * @priv: Data for the step functions.
  * @priv2: More data for the step functions.
  * @ustep: Function for UBUF/IOVEC iterators; given __user addresses.
  * @step: Function for other iterators; given kernel addresses.
  *
  * Iterate over the next part of an iterator, up to the specified length.  The
  * buffer is presented in segments, which for kernel iteration are broken up by
  * physical pages and mapped, with the mapped address being presented.
  *
  * Two step functions, @step and @ustep, must be provided, one for handling
  * mapped kernel addresses and the other is given user addresses which have the
  * potential to fault since no pinning is performed.
  *
  * The step functions are passed the address and length of the segment, @priv,
  * @priv2 and the amount of data so far iterated over (which can, for example,
  * be added to @priv to point to the right part of a second buffer).  The step
  * functions should return the amount of the segment they didn't process (ie. 0
  * indicates complete processsing).
  *
  * This function returns the amount of data processed (ie. 0 means nothing was
  * processed and the value of @len means processes to completion).
  */
 static __always_inline
 size_t iterate_and_advance2(struct iov_iter *iter, size_t len, void *priv,
 			    void *priv2, iov_ustep_f ustep, iov_step_f step)
 {
 	if (unlikely(iter->count < len))
 		len = iter->count;
 	if (unlikely(!len))
 		return 0;

 	if (likely(iter_is_ubuf(iter)))
 		return iterate_ubuf(iter, len, priv, priv2, ustep);
 	if (likely(iter_is_iovec(iter)))
 		return iterate_iovec(iter, len, priv, priv2, ustep);
 	if (iov_iter_is_bvec(iter))
 		return iterate_bvec(iter, len, priv, priv2, step);
 	if (iov_iter_is_kvec(iter))
 		return iterate_kvec(iter, len, priv, priv2, step);
 	if (iov_iter_is_xarray(iter))
 		return iterate_xarray(iter, len, priv, priv2, step);
 	return iterate_discard(iter, len, priv, priv2, step);
 }

 /**
  * iterate_and_advance - Iterate over an iterator
  * @iter: The iterator to iterate over.
  * @len: The amount to iterate over.
  * @priv: Data for the step functions.
  * @ustep: Function for UBUF/IOVEC iterators; given __user addresses.
  * @step: Function for other iterators; given kernel addresses.
  *
  * As iterate_and_advance2(), but priv2 is always NULL.
  */
 static __always_inline
 size_t iterate_and_advance(struct iov_iter *iter, size_t len, void *priv,
 			   iov_ustep_f ustep, iov_step_f step)
 {
 	return iterate_and_advance2(iter, len, priv, NULL, ustep, step);
 }

 #endif /* _LINUX_IOV_ITER_H */
	/* SPDX-License-Identifier: GPL-2.0-or-later */
	/* I/O iterator iteration building functions.
	*
	* Copyright (C) 2023 Red Hat, Inc. All Rights Reserved.
	* Written by David Howells (dhowells@redhat.com)
	*/

	#ifndef _LINUX_IOV_ITER_H
	#define _LINUX_IOV_ITER_H

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

	typedef size_t (iov_step_f)(void iter_base, size_t progress, size_t len,
	void priv, void priv2);
	typedef size_t (iov_ustep_f)(void __user iter_base, size_t progress, size_t len,
	void priv, void priv2);

	/*
	* Handle ITER_UBUF.
	*/
	static __always_inline
	size_t iterate_ubuf(struct iov_iter iter, size_t len, void priv, void *priv2,
	iov_ustep_f step)
	{
	void __user *base = iter->ubuf;
	size_t progress = 0, remain;

	remain = step(base + iter->iov_offset, 0, len, priv, priv2);
	progress = len - remain;
	iter->iov_offset += progress;
	iter->count -= progress;
	return progress;
	}

	/*
	* Handle ITER_IOVEC.
	*/
	static __always_inline
	size_t iterate_iovec(struct iov_iter iter, size_t len, void priv, void *priv2,
	iov_ustep_f step)
	{
	const struct iovec *p = iter->__iov;
	size_t progress = 0, skip = iter->iov_offset;

	do {
	size_t remain, consumed;
	size_t part = min(len, p->iov_len - skip);

	if (likely(part)) {
	remain = step(p->iov_base + skip, progress, part, priv, priv2);
	consumed = part - remain;
	progress += consumed;
	skip += consumed;
	len -= consumed;
	if (skip < p->iov_len)
	break;
	}
	p++;
	skip = 0;
	} while (len);

	iter->nr_segs -= p - iter->__iov;
	iter->__iov = p;
	iter->iov_offset = skip;
	iter->count -= progress;
	return progress;
	}

	/*
	* Handle ITER_KVEC.
	*/
	static __always_inline
	size_t iterate_kvec(struct iov_iter iter, size_t len, void priv, void *priv2,
	iov_step_f step)
	{
	const struct kvec *p = iter->kvec;
	size_t progress = 0, skip = iter->iov_offset;

	do {
	size_t remain, consumed;
	size_t part = min(len, p->iov_len - skip);

	if (likely(part)) {
	remain = step(p->iov_base + skip, progress, part, priv, priv2);
	consumed = part - remain;
	progress += consumed;
	skip += consumed;
	len -= consumed;
	if (skip < p->iov_len)
	break;
	}
	p++;
	skip = 0;
	} while (len);

	iter->nr_segs -= p - iter->kvec;
	iter->kvec = p;
	iter->iov_offset = skip;
	iter->count -= progress;
	return progress;
	}

	/*
	* Handle ITER_BVEC.
	*/
	static __always_inline
	size_t iterate_bvec(struct iov_iter iter, size_t len, void priv, void *priv2,
	iov_step_f step)
	{
	const struct bio_vec *p = iter->bvec;
	size_t progress = 0, skip = iter->iov_offset;

	do {
	size_t remain, consumed;
	size_t offset = p->bv_offset + skip, part;
	void *kaddr = kmap_local_page(p->bv_page + offset / PAGE_SIZE);

	part = min3(len,
	(size_t)(p->bv_len - skip),
	(size_t)(PAGE_SIZE - offset % PAGE_SIZE));
	remain = step(kaddr + offset % PAGE_SIZE, progress, part, priv, priv2);
	kunmap_local(kaddr);
	consumed = part - remain;
	len -= consumed;
	progress += consumed;
	skip += consumed;
	if (skip >= p->bv_len) {
	skip = 0;
	p++;
	}
	if (remain)
	break;
	} while (len);

	iter->nr_segs -= p - iter->bvec;
	iter->bvec = p;
	iter->iov_offset = skip;
	iter->count -= progress;
	return progress;
	}

	/*
	* Handle ITER_XARRAY.
	*/
	static __always_inline
	size_t iterate_xarray(struct iov_iter iter, size_t len, void priv, void *priv2,
	iov_step_f step)
	{
	struct folio *folio;
	size_t progress = 0;
	loff_t start = iter->xarray_start + iter->iov_offset;
	pgoff_t index = start / PAGE_SIZE;
	XA_STATE(xas, iter->xarray, index);

	rcu_read_lock();
	xas_for_each(&xas, folio, ULONG_MAX) {
	size_t remain, consumed, offset, part, flen;

	if (xas_retry(&xas, folio))
	continue;
	if (WARN_ON(xa_is_value(folio)))
	break;
	if (WARN_ON(folio_test_hugetlb(folio)))
	break;

	offset = offset_in_folio(folio, start + progress);
	flen = min(folio_size(folio) - offset, len);

	while (flen) {
	void *base = kmap_local_folio(folio, offset);

	part = min_t(size_t, flen,
	PAGE_SIZE - offset_in_page(offset));
	remain = step(base, progress, part, priv, priv2);
	kunmap_local(base);

	consumed = part - remain;
	progress += consumed;
	len -= consumed;

	if (remain \|\| len == 0)
	goto out;
	flen -= consumed;
	offset += consumed;
	}
	}

	out:
	rcu_read_unlock();
	iter->iov_offset += progress;
	iter->count -= progress;
	return progress;
	}

	/*
	* Handle ITER_DISCARD.
	*/
	static __always_inline
	size_t iterate_discard(struct iov_iter iter, size_t len, void priv, void *priv2,
	iov_step_f step)
	{
	size_t progress = len;

	iter->count -= progress;
	return progress;
	}

	/**
	* iterate_and_advance2 - Iterate over an iterator
	* @iter: The iterator to iterate over.
	* @len: The amount to iterate over.
	* @priv: Data for the step functions.
	* @priv2: More data for the step functions.
	* @ustep: Function for UBUF/IOVEC iterators; given __user addresses.
	* @step: Function for other iterators; given kernel addresses.
	*
	* Iterate over the next part of an iterator, up to the specified length. The
	* buffer is presented in segments, which for kernel iteration are broken up by
	* physical pages and mapped, with the mapped address being presented.
	*
	* Two step functions, @step and @ustep, must be provided, one for handling
	* mapped kernel addresses and the other is given user addresses which have the
	* potential to fault since no pinning is performed.
	*
	* The step functions are passed the address and length of the segment, @priv,
	* @priv2 and the amount of data so far iterated over (which can, for example,
	* be added to @priv to point to the right part of a second buffer). The step
	* functions should return the amount of the segment they didn't process (ie. 0
	* indicates complete processsing).
	*
	* This function returns the amount of data processed (ie. 0 means nothing was
	* processed and the value of @len means processes to completion).
	*/
	static __always_inline
	size_t iterate_and_advance2(struct iov_iter iter, size_t len, void priv,
	void *priv2, iov_ustep_f ustep, iov_step_f step)
	{
	if (unlikely(iter->count < len))
	len = iter->count;
	if (unlikely(!len))
	return 0;

	if (likely(iter_is_ubuf(iter)))
	return iterate_ubuf(iter, len, priv, priv2, ustep);
	if (likely(iter_is_iovec(iter)))
	return iterate_iovec(iter, len, priv, priv2, ustep);
	if (iov_iter_is_bvec(iter))
	return iterate_bvec(iter, len, priv, priv2, step);
	if (iov_iter_is_kvec(iter))
	return iterate_kvec(iter, len, priv, priv2, step);
	if (iov_iter_is_xarray(iter))
	return iterate_xarray(iter, len, priv, priv2, step);
	return iterate_discard(iter, len, priv, priv2, step);
	}

	/**
	* iterate_and_advance - Iterate over an iterator
	* @iter: The iterator to iterate over.
	* @len: The amount to iterate over.
	* @priv: Data for the step functions.
	* @ustep: Function for UBUF/IOVEC iterators; given __user addresses.
	* @step: Function for other iterators; given kernel addresses.
	*
	* As iterate_and_advance2(), but priv2 is always NULL.
	*/
	static __always_inline
	size_t iterate_and_advance(struct iov_iter iter, size_t len, void priv,
	iov_ustep_f ustep, iov_step_f step)
	{
	return iterate_and_advance2(iter, len, priv, NULL, ustep, step);
	}

	#endif /* _LINUX_IOV_ITER_H */