text: /* SPDX-License-Identifier: GPL-2.0 */
  /*
   * bvec iterator
   *
   * Copyright (C) 2001 Ming Lei <ming.lei@canonical.com>
   */
  #ifndef __LINUX_BVEC_H
  #define __LINUX_BVEC_H
  
  #include <linux/highmem.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 */
  } __packed;
  
  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;
  }
  
  /*
   * A simpler version of bvec_iter_advance(), @bytes should not span
   * across multiple bvec entries, i.e. bytes <= bv[i->bi_idx].bv_len
   */
  static inline void bvec_iter_advance_single(const struct bio_vec *bv,
  				struct bvec_iter *iter, unsigned int bytes)
  {
  	unsigned int done = iter->bi_bvec_done + bytes;
  
  	if (done == bv[iter->bi_idx].bv_len) {
  		done = 0;
  		iter->bi_idx++;
  	}
  	iter->bi_bvec_done = done;
  	iter->bi_size -= bytes;
  }
  
  #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_single((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;
  	}
  }
  
  /**
   * bvec_kmap_local - map a bvec into the kernel virtual address space
   * @bvec: bvec to map
   *
   * Must be called on single-page bvecs only.  Call kunmap_local on the returned
   * address to unmap.
   */
  static inline void *bvec_kmap_local(struct bio_vec *bvec)
  {
  	return kmap_local_page(bvec->bv_page) + bvec->bv_offset;
  }
  
  /**
   * memcpy_from_bvec - copy data from a bvec
   * @bvec: bvec to copy from
   *
   * Must be called on single-page bvecs only.
   */
  static inline void memcpy_from_bvec(char *to, struct bio_vec *bvec)
  {
  	memcpy_from_page(to, bvec->bv_page, bvec->bv_offset, bvec->bv_len);
  }
  
  /**
   * memcpy_to_bvec - copy data to a bvec
   * @bvec: bvec to copy to
   *
   * Must be called on single-page bvecs only.
   */
  static inline void memcpy_to_bvec(struct bio_vec *bvec, const char *from)
  {
  	memcpy_to_page(bvec->bv_page, bvec->bv_offset, from, bvec->bv_len);
  }
  
  /**
   * memzero_bvec - zero all data in a bvec
   * @bvec: bvec to zero
   *
   * Must be called on single-page bvecs only.
   */
  static inline void memzero_bvec(struct bio_vec *bvec)
  {
  	memzero_page(bvec->bv_page, bvec->bv_offset, bvec->bv_len);
  }
  
  /**
   * bvec_virt - return the virtual address for a bvec
   * @bvec: bvec to return the virtual address for
   *
   * Note: the caller must ensure that @bvec->bv_page is not a highmem page.
   */
  static inline void *bvec_virt(struct bio_vec *bvec)
  {
  	WARN_ON_ONCE(PageHighMem(bvec->bv_page));
  	return page_address(bvec->bv_page) + bvec->bv_offset;
  }
  
  #endif /* __LINUX_BVEC_H */
  