Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S945393AbcJaSAB (ORCPT ); Mon, 31 Oct 2016 14:00:01 -0400 Received: from bombadil.infradead.org ([198.137.202.9]:49234 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S945308AbcJaR7a (ORCPT ); Mon, 31 Oct 2016 13:59:30 -0400 From: Christoph Hellwig To: axboe@fb.com Cc: linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, Kent Overstreet Subject: [PATCH 1/2] block: add bio_iov_iter_get_pages() Date: Mon, 31 Oct 2016 11:59:24 -0600 Message-Id: <1477936765-8828-2-git-send-email-hch@lst.de> X-Mailer: git-send-email 2.1.4 In-Reply-To: <1477936765-8828-1-git-send-email-hch@lst.de> References: <1477936765-8828-1-git-send-email-hch@lst.de> X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org. See http://www.infradead.org/rpr.html Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3214 Lines: 91 From: Kent Overstreet 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 [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 --- block/bio.c | 49 +++++++++++++++++++++++++++++++++++++++++++++++++ include/linux/bio.h | 1 + 2 files changed, 50 insertions(+) diff --git a/block/bio.c b/block/bio.c index db85c57..2cf6eba 100644 --- a/block/bio.c +++ b/block/bio.c @@ -847,6 +847,55 @@ int bio_add_page(struct bio *bio, struct page *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 completion event; int error; diff --git a/include/linux/bio.h b/include/linux/bio.h index 87ce64d..c39fa0b 100644 --- a/include/linux/bio.h +++ b/include/linux/bio.h @@ -419,6 +419,7 @@ void bio_chain(struct bio *, struct bio *); extern int bio_add_page(struct bio *, struct page *, unsigned int,unsigned int); extern int bio_add_pc_page(struct request_queue *, struct bio *, struct page *, unsigned int, unsigned int); +int bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter); struct rq_map_data; extern struct bio *bio_map_user_iov(struct request_queue *, const struct iov_iter *, gfp_t); -- 2.1.4