Return-Path: Received: from mx1.redhat.com ([209.132.183.28]:58280 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726224AbeKZNNv (ORCPT ); Mon, 26 Nov 2018 08:13:51 -0500 From: Ming Lei To: Jens Axboe Cc: linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Theodore Ts'o , Omar Sandoval , Sagi Grimberg , Dave Chinner , Kent Overstreet , Mike Snitzer , dm-devel@redhat.com, Alexander Viro , linux-fsdevel@vger.kernel.org, Shaohua Li , linux-raid@vger.kernel.org, David Sterba , linux-btrfs@vger.kernel.org, "Darrick J . Wong" , linux-xfs@vger.kernel.org, Gao Xiang , Christoph Hellwig , linux-ext4@vger.kernel.org, Coly Li , linux-bcache@vger.kernel.org, Boaz Harrosh , Bob Peterson , cluster-devel@redhat.com, Ming Lei Subject: [PATCH V12 18/20] block: document usage of bio iterator helpers Date: Mon, 26 Nov 2018 10:17:18 +0800 Message-Id: <20181126021720.19471-19-ming.lei@redhat.com> In-Reply-To: <20181126021720.19471-1-ming.lei@redhat.com> References: <20181126021720.19471-1-ming.lei@redhat.com> Sender: linux-ext4-owner@vger.kernel.org List-ID: Now multi-page bvec is supported, some helpers may return page by page, meantime some may return segment by segment, this patch documents the usage. Signed-off-by: Ming Lei --- Documentation/block/biovecs.txt | 25 +++++++++++++++++++++++++ 1 file changed, 25 insertions(+) diff --git a/Documentation/block/biovecs.txt b/Documentation/block/biovecs.txt index 25689584e6e0..ce6eccaf5df7 100644 --- a/Documentation/block/biovecs.txt +++ b/Documentation/block/biovecs.txt @@ -117,3 +117,28 @@ Other implications: size limitations and the limitations of the underlying devices. Thus there's no need to define ->merge_bvec_fn() callbacks for individual block drivers. + +Usage of helpers: +================= + +* The following helpers whose names have the suffix of "_all" can only be used +on non-BIO_CLONED bio. They are usually used by filesystem code. Drivers +shouldn't use them because the bio may have been split before it reached the +driver. + + bio_for_each_segment_all() + bio_first_bvec_all() + bio_first_page_all() + bio_last_bvec_all() + +* The following helpers iterate over single-page segment. The passed 'struct +bio_vec' will contain a single-page IO vector during the iteration + + bio_for_each_segment() + bio_for_each_segment_all() + +* The following helpers iterate over multi-page bvec. The passed 'struct +bio_vec' will contain a multi-page IO vector during the iteration + + bio_for_each_bvec() + rq_for_each_bvec() -- 2.9.5