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: Kent 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: Christoph Hellwig <hch@lst.de> Signed-off-by: Jens Axboe <axboe@fb.com> (cherry picked from commit 9cd56d916aa481ce8f56d9c5302a6ed90c2e0b5f)
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parent
e3df41f978
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3816199506
49
block/bio.c
49
block/bio.c
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@ -847,6 +847,55 @@ done:
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}
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}
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EXPORT_SYMBOL(bio_add_page);
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EXPORT_SYMBOL(bio_add_page);
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/**
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* bio_iov_iter_get_pages - pin user or kernel pages and add them to a bio
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* @bio: bio to add pages to
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* @iter: iov iterator describing the region to be mapped
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*
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* Pins as many pages from *iter and appends them to @bio's bvec array. The
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* pages will have to be released using put_page() when done.
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*/
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int bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
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{
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unsigned short nr_pages = bio->bi_max_vecs - bio->bi_vcnt;
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struct bio_vec *bv = bio->bi_io_vec + bio->bi_vcnt;
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struct page **pages = (struct page **)bv;
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size_t offset, diff;
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ssize_t size;
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size = iov_iter_get_pages(iter, pages, LONG_MAX, nr_pages, &offset);
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if (unlikely(size <= 0))
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return size ? size : -EFAULT;
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nr_pages = (size + offset + PAGE_SIZE - 1) / PAGE_SIZE;
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/*
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* Deep magic below: We need to walk the pinned pages backwards
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* because we are abusing the space allocated for the bio_vecs
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* for the page array. Because the bio_vecs are larger than the
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* page pointers by definition this will always work. But it also
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* means we can't use bio_add_page, so any changes to it's semantics
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* need to be reflected here as well.
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*/
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bio->bi_iter.bi_size += size;
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bio->bi_vcnt += nr_pages;
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diff = (nr_pages * PAGE_SIZE - offset) - size;
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while (nr_pages--) {
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bv[nr_pages].bv_page = pages[nr_pages];
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bv[nr_pages].bv_len = PAGE_SIZE;
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bv[nr_pages].bv_offset = 0;
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}
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bv[0].bv_offset += offset;
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bv[0].bv_len -= offset;
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if (diff)
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bv[bio->bi_vcnt - 1].bv_len -= diff;
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iov_iter_advance(iter, size);
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return 0;
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}
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EXPORT_SYMBOL_GPL(bio_iov_iter_get_pages);
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struct submit_bio_ret {
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struct submit_bio_ret {
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struct completion event;
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struct completion event;
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int error;
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int error;
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@ -430,6 +430,7 @@ void bio_chain(struct bio *, struct bio *);
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extern int bio_add_page(struct bio *, struct page *, unsigned int,unsigned int);
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extern int bio_add_page(struct bio *, struct page *, unsigned int,unsigned int);
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extern int bio_add_pc_page(struct request_queue *, struct bio *, struct page *,
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extern int bio_add_pc_page(struct request_queue *, struct bio *, struct page *,
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unsigned int, unsigned int);
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unsigned int, unsigned int);
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int bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter);
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struct rq_map_data;
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struct rq_map_data;
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extern struct bio *bio_map_user_iov(struct request_queue *,
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extern struct bio *bio_map_user_iov(struct request_queue *,
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const struct iov_iter *, gfp_t);
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const struct iov_iter *, gfp_t);
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