alistair23-linux/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/bug.h>
#include <linux/errno.h>
#include <linux/limits.h>
#include <linux/minmax.h>
#include <linux/mm.h>
#include <linux/types.h>

struct page;

/**
 * struct bio_vec - a contiguous range of physical memory addresses
 * @bv_page:   First page associated with the address range.
 * @bv_len:    Number of bytes in the address range.
 * @bv_offset: Start of the address range relative to the start of @bv_page.
 *
 * The following holds for a bvec if n * PAGE_SIZE < bv_offset + bv_len:
 *
 *   nth_page(@bv_page, n) == @bv_page + n
 *
 * This holds because page_is_mergeable() checks the above property.
 */
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)
{
	unsigned int idx = iter->bi_idx;

	if (WARN_ONCE(bytes > iter->bi_size,
		     "Attempted to advance past end of bvec iter\n")) {
		iter->bi_size = 0;
		return false;
	}

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

	while (bytes && bytes >= bv[idx].bv_len) {
		bytes -= bv[idx].bv_len;
		idx++;
	}

	iter->bi_idx = idx;
	iter->bi_bvec_done = bytes;
	return true;
}

static inline void bvec_iter_skip_zero_bvec(struct bvec_iter *iter)
{
	iter->bi_bvec_done = 0;
	iter->bi_idx++;
}

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

/* 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;
	}
}

#endif /* __LINUX_BVEC_ITER_H */