kernel/include/linux/bvec.h

/* SPDX-License-Identifier: GPL-2.0 */
/*
 * bvec iterator
 *
 * Copyright (C) 2001 Ming Lei <ming.lei@canonical.com>
 */
#ifndef __LINUX_BVEC_ITER_H
#define __LINUX_BVEC_ITER_H

#include <linux/kernel.h>
#include <linux/bug.h>
#include <linux/errno.h>
#include <linux/mm.h>

/*
 * was unsigned short, but we might as well be ready for > 64kB I/O pages
 */
struct bio_vec {
	struct page	*bv_page;
	unsigned int	bv_len;
	unsigned int	bv_offset;
};

struct bvec_iter {
	sector_t		bi_sector;	/* device address in 512 byte
						   sectors */
	unsigned int		bi_size;	/* residual I/O count */

	unsigned int		bi_idx;		/* current index into bvl_vec */

	unsigned int            bi_bvec_done;	/* number of bytes completed in
						   current bvec */
};

struct bvec_iter_all {
	struct bio_vec	bv;
	int		idx;
	unsigned	done;
};

/*
 * various member access, note that bio_data should of course not be used
 * on highmem page vectors
 */
#define __bvec_iter_bvec(bvec, iter)	(&(bvec)[(iter).bi_idx])

/* multi-page (mp_bvec) helpers */
#define mp_bvec_iter_page(bvec, iter)				\
	(__bvec_iter_bvec((bvec), (iter))->bv_page)

#define mp_bvec_iter_len(bvec, iter)				\
	min((iter).bi_size,					\
	    __bvec_iter_bvec((bvec), (iter))->bv_len - (iter).bi_bvec_done)

#define mp_bvec_iter_offset(bvec, iter)				\
	(__bvec_iter_bvec((bvec), (iter))->bv_offset + (iter).bi_bvec_done)

#define mp_bvec_iter_page_idx(bvec, iter)			\
	(mp_bvec_iter_offset((bvec), (iter)) / PAGE_SIZE)

#define mp_bvec_iter_bvec(bvec, iter)				\
((struct bio_vec) {						\
	.bv_page	= mp_bvec_iter_page((bvec), (iter)),	\
	.bv_len		= mp_bvec_iter_len((bvec), (iter)),	\
	.bv_offset	= mp_bvec_iter_offset((bvec), (iter)),	\
})

/* For building single-page bvec in flight */
 #define bvec_iter_offset(bvec, iter)				\
	(mp_bvec_iter_offset((bvec), (iter)) % PAGE_SIZE)

#define bvec_iter_len(bvec, iter)				\
	min_t(unsigned, mp_bvec_iter_len((bvec), (iter)),		\
	      PAGE_SIZE - bvec_iter_offset((bvec), (iter)))

#define bvec_iter_page(bvec, iter)				\
	(mp_bvec_iter_page((bvec), (iter)) +			\
	 mp_bvec_iter_page_idx((bvec), (iter)))

#define bvec_iter_bvec(bvec, iter)				\
((struct bio_vec) {						\
	.bv_page	= bvec_iter_page((bvec), (iter)),	\
	.bv_len		= bvec_iter_len((bvec), (iter)),	\
	.bv_offset	= bvec_iter_offset((bvec), (iter)),	\
})

static inline bool bvec_iter_advance(const struct bio_vec *bv,
		struct bvec_iter *iter, unsigned bytes)
{
	if (WARN_ONCE(bytes > iter->bi_size,
		     "Attempted to advance past end of bvec iter\n")) {
		iter->bi_size = 0;
		return false;
	}

	while (bytes) {
		const struct bio_vec *cur = bv + iter->bi_idx;
		unsigned len = min3(bytes, iter->bi_size,
				    cur->bv_len - iter->bi_bvec_done);

		bytes -= len;
		iter->bi_size -= len;
		iter->bi_bvec_done += len;

		if (iter->bi_bvec_done == cur->bv_len) {
			iter->bi_bvec_done = 0;
			iter->bi_idx++;
		}
	}
	return true;
}

#define for_each_bvec(bvl, bio_vec, iter, start)			\
	for (iter = (start);						\
	     (iter).bi_size &&						\
		((bvl = bvec_iter_bvec((bio_vec), (iter))), 1);	\
	     bvec_iter_advance((bio_vec), &(iter), (bvl).bv_len))

/* for iterating one bio from start to end */
#define BVEC_ITER_ALL_INIT (struct bvec_iter)				\
{									\
	.bi_sector	= 0,						\
	.bi_size	= UINT_MAX,					\
	.bi_idx		= 0,						\
	.bi_bvec_done	= 0,						\
}

static inline struct bio_vec *bvec_init_iter_all(struct bvec_iter_all *iter_all)
{
	iter_all->done = 0;
	iter_all->idx = 0;

	return &iter_all->bv;
}

static inline void bvec_advance(const struct bio_vec *bvec,
				struct bvec_iter_all *iter_all)
{
	struct bio_vec *bv = &iter_all->bv;

	if (iter_all->done) {
		bv->bv_page++;
		bv->bv_offset = 0;
	} else {
		bv->bv_page = bvec->bv_page + (bvec->bv_offset >> PAGE_SHIFT);
		bv->bv_offset = bvec->bv_offset & ~PAGE_MASK;
	}
	bv->bv_len = min_t(unsigned int, PAGE_SIZE - bv->bv_offset,
			   bvec->bv_len - iter_all->done);
	iter_all->done += bv->bv_len;

	if (iter_all->done == bvec->bv_len) {
		iter_all->idx++;
		iter_all->done = 0;
	}
}

/*
 * Get the last single-page segment from the multi-page bvec and store it
 * in @seg
 */
static inline void mp_bvec_last_segment(const struct bio_vec *bvec,
					struct bio_vec *seg)
{
	unsigned total = bvec->bv_offset + bvec->bv_len;
	unsigned last_page = (total - 1) / PAGE_SIZE;

	seg->bv_page = bvec->bv_page + last_page;

	/* the whole segment is inside the last page */
	if (bvec->bv_offset >= last_page * PAGE_SIZE) {
		seg->bv_offset = bvec->bv_offset % PAGE_SIZE;
		seg->bv_len = bvec->bv_len;
	} else {
		seg->bv_offset = 0;
		seg->bv_len = total - last_page * PAGE_SIZE;
	}
}

#endif /* __LINUX_BVEC_ITER_H */