From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f194.google.com ([209.85.192.194]:35074 "EHLO mail-pf0-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S942968AbcJ2IOT (ORCPT ); Sat, 29 Oct 2016 04:14:19 -0400 From: Ming Lei To: Jens Axboe , linux-kernel@vger.kernel.org Cc: linux-block@vger.kernel.org, linux-fsdevel@vger.kernel.org, Christoph Hellwig , "Kirill A . Shutemov" , Ming Lei , Johannes Berg Subject: [PATCH 31/60] block: introduce multipage/single page bvec helpers Date: Sat, 29 Oct 2016 16:08:30 +0800 Message-Id: <1477728600-12938-32-git-send-email-tom.leiming@gmail.com> In-Reply-To: <1477728600-12938-1-git-send-email-tom.leiming@gmail.com> References: <1477728600-12938-1-git-send-email-tom.leiming@gmail.com> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: This patch introduces helpers which are suffixed with _mp and _sp for the multipage bvec/segment support. The helpers with _mp suffix are the interfaces for treating one bvec/segment as real multipage one, for example, .bv_len is the total length of the multipage segment. The helpers with _sp suffix are interfaces for supporting current bvec iterator which is thought as singlepage only by drivers, fs, dm and etc. These _sp helpers are introduced to build singlepage bvec in flight, so users of bio/bvec iterator still can work well and needn't change even though we store multipage into bvec. Signed-off-by: Ming Lei --- include/linux/bvec.h | 57 +++++++++++++++++++++++++++++++++++++++++++++++++--- 1 file changed, 54 insertions(+), 3 deletions(-) diff --git a/include/linux/bvec.h b/include/linux/bvec.h index 89b65b82d98f..da984fa171bc 100644 --- a/include/linux/bvec.h +++ b/include/linux/bvec.h @@ -24,6 +24,42 @@ #include /* + * What is multipage bvecs(segment)? + * + * - bvec stored in bio->bi_io_vec is always multipage style vector + * + * - bvec(struct bio_vec) represents one physically contiguous I/O + * buffer, now the buffer may include more than one pages since + * multipage(mp) bvec is supported, and all these pages represented + * by one bvec is physically contiguous. Before mp support, at most + * one page can be included in one bvec, we call it singlepage(sp) + * bvec. + * + * - .bv_page of th bvec represents the 1st page in the mp segment + * + * - .bv_offset of the bvec represents offset of the buffer in the bvec + * + * The effect on the current drivers/filesystem/dm/bcache/...: + * + * - almost everyone supposes that one bvec only includes one single + * page, so we keep the sp interface not changed, for example, + * bio_for_each_segment() still returns bvec with single page + * + * - bio_for_each_segment_all() will be changed to return singlepage + * bvec too + * + * - during iterating, iterator variable(struct bvec_iter) is always + * updated in multipage bvec style and that means bvec_iter_advance() + * is kept not changed + * + * - returned(copied) singlepage bvec is generated in flight from bvec + * helpers + * + * - In case that some components(such as iov_iter) need to support mp + * segment, we introduce new helpers(suffixed with _mp) for them. + */ + +/* * was unsigned short, but we might as well be ready for > 64kB I/O pages */ struct bio_vec { @@ -49,16 +85,31 @@ struct bvec_iter { */ #define __bvec_iter_bvec(bvec, iter) (&(bvec)[(iter).bi_idx]) -#define bvec_iter_page(bvec, iter) \ +#define bvec_iter_page_mp(bvec, iter) \ (__bvec_iter_bvec((bvec), (iter))->bv_page) -#define bvec_iter_len(bvec, iter) \ +#define bvec_iter_len_mp(bvec, iter) \ min((iter).bi_size, \ __bvec_iter_bvec((bvec), (iter))->bv_len - (iter).bi_bvec_done) -#define bvec_iter_offset(bvec, iter) \ +#define bvec_iter_offset_mp(bvec, iter) \ (__bvec_iter_bvec((bvec), (iter))->bv_offset + (iter).bi_bvec_done) +/* + * of sp segment. + * + * This helpers will be implemented for building sp bvec in flight. + * + */ +#define bvec_iter_offset_sp(bvec, iter) bvec_iter_offset_mp((bvec), (iter)) +#define bvec_iter_len_sp(bvec, iter) bvec_iter_len_mp((bvec), (iter)) +#define bvec_iter_page_sp(bvec, iter) bvec_iter_page_mp((bvec), (iter)) + +/* current interfaces support sp style at default */ +#define bvec_iter_page(bvec, iter) bvec_iter_page_sp((bvec), (iter)) +#define bvec_iter_len(bvec, iter) bvec_iter_len_sp((bvec), (iter)) +#define bvec_iter_offset(bvec, iter) bvec_iter_offset_sp((bvec), (iter)) + #define bvec_iter_bvec(bvec, iter) \ ((struct bio_vec) { \ .bv_page = bvec_iter_page((bvec), (iter)), \ -- 2.7.4