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Commit 2cefe4db authored by Kent Overstreet's avatar Kent Overstreet Committed by Jens Axboe
Browse files

block: add bio_iov_iter_get_pages() 



This is a helper that pins down a range from an iov_iter and adds it to
a bio without requiring a separate memory allocation for the page array.
It will be used for upcoming direct I/O implementations for block devices
and iomap based file systems.

Signed-off-by: default avatarKent Overstreet <kent.overstreet@gmail.com>
[hch: ported to the iov_iter interface, renamed and added comments.
      All blame should be directed to me and all fame should go to Kent
      after this!]
Signed-off-by: default avatarChristoph Hellwig <hch@lst.de>
Signed-off-by: default avatarJens Axboe <axboe@fb.com>
parent 13edd5e7

block/bio.c

+49 −0
Original line number Original line Diff line number Diff line
@@ -847,6 +847,55 @@ int bio_add_page(struct bio *bio, struct page *page, 
}

}

EXPORT_SYMBOL(bio_add_page);

EXPORT_SYMBOL(bio_add_page);





/**

 * bio_iov_iter_get_pages - pin user or kernel pages and add them to a bio

 * @bio: bio to add pages to

 * @iter: iov iterator describing the region to be mapped

 *

 * Pins as many pages from *iter and appends them to @bio's bvec array. The

 * pages will have to be released using put_page() when done.

 */

int bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)

{

	unsigned short nr_pages = bio->bi_max_vecs - bio->bi_vcnt;

	struct bio_vec *bv = bio->bi_io_vec + bio->bi_vcnt;

	struct page **pages = (struct page **)bv;

	size_t offset, diff;

	ssize_t size;



	size = iov_iter_get_pages(iter, pages, LONG_MAX, nr_pages, &offset);

	if (unlikely(size <= 0))

		return size ? size : -EFAULT;

	nr_pages = (size + offset + PAGE_SIZE - 1) / PAGE_SIZE;



	/*

	 * Deep magic below:  We need to walk the pinned pages backwards

	 * because we are abusing the space allocated for the bio_vecs

	 * for the page array.  Because the bio_vecs are larger than the

	 * page pointers by definition this will always work.  But it also

	 * means we can't use bio_add_page, so any changes to it's semantics

	 * need to be reflected here as well.

	 */

	bio->bi_iter.bi_size += size;

	bio->bi_vcnt += nr_pages;



	diff = (nr_pages * PAGE_SIZE - offset) - size;

	while (nr_pages--) {

		bv[nr_pages].bv_page = pages[nr_pages];

		bv[nr_pages].bv_len = PAGE_SIZE;

		bv[nr_pages].bv_offset = 0;

	}



	bv[0].bv_offset += offset;

	bv[0].bv_len -= offset;

	if (diff)

		bv[bio->bi_vcnt - 1].bv_len -= diff;



	iov_iter_advance(iter, size);

	return 0;

}

EXPORT_SYMBOL_GPL(bio_iov_iter_get_pages);



struct submit_bio_ret {

struct submit_bio_ret {

	struct completion event;

	struct completion event;

	int error;

	int error;

include/linux/bio.h

+1 −0
Original line number Original line Diff line number Diff line
@@ -427,6 +427,7 @@ void bio_chain(struct bio *, struct bio *); 
extern int bio_add_page(struct bio *, struct page *, unsigned int,unsigned int);

extern int bio_add_page(struct bio *, struct page *, unsigned int,unsigned int);

extern int bio_add_pc_page(struct request_queue *, struct bio *, struct page *,

extern int bio_add_pc_page(struct request_queue *, struct bio *, struct page *,

			   unsigned int, unsigned int);

			   unsigned int, unsigned int);

int bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter);

struct rq_map_data;

struct rq_map_data;

extern struct bio *bio_map_user_iov(struct request_queue *,

extern struct bio *bio_map_user_iov(struct request_queue *,

				    const struct iov_iter *, gfp_t);

				    const struct iov_iter *, gfp_t);