Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965191AbcKABFE (ORCPT ); Mon, 31 Oct 2016 21:05:04 -0400 Received: from mail-vk0-f65.google.com ([209.85.213.65]:34202 "EHLO mail-vk0-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S948415AbcKABFC (ORCPT ); Mon, 31 Oct 2016 21:05:02 -0400 MIME-Version: 1.0 In-Reply-To: <1477936765-8828-2-git-send-email-hch@lst.de> References: <1477936765-8828-1-git-send-email-hch@lst.de> <1477936765-8828-2-git-send-email-hch@lst.de> From: Ming Lei Date: Tue, 1 Nov 2016 09:05:00 +0800 Message-ID: Subject: Re: [PATCH 1/2] block: add bio_iov_iter_get_pages() To: Christoph Hellwig Cc: Jens Axboe , linux-block , Linux Kernel Mailing List , Kent Overstreet Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4093 Lines: 106 On Tue, Nov 1, 2016 at 1:59 AM, Christoph Hellwig wrote: > 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); BTW, if there is one multi-page version of get_user_pages_fast() and iov_iter_get_pages(), size of page array can be reduced too. > + 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 > > -- > To unsubscribe from this list: send the line "unsubscribe linux-block" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html -- Ming Lei