From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id AEBC2C43441 for ; Tue, 13 Nov 2018 15:16:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7F0A322510 for ; Tue, 13 Nov 2018 15:16:54 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 7F0A322510 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-block-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732817AbeKNBPW (ORCPT ); Tue, 13 Nov 2018 20:15:22 -0500 Received: from mx1.redhat.com ([209.132.183.28]:51662 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2388204AbeKNBPV (ORCPT ); Tue, 13 Nov 2018 20:15:21 -0500 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 47BED30020C7; Tue, 13 Nov 2018 15:16:47 +0000 (UTC) Received: from localhost (ovpn-8-23.pek2.redhat.com [10.72.8.23]) by smtp.corp.redhat.com (Postfix) with ESMTP id 732D9605C6; Tue, 13 Nov 2018 15:16:46 +0000 (UTC) From: Ming Lei To: Jens Axboe Cc: linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, Ming Lei , Christoph Hellwig Subject: [PATCH V9 16/19] block: document usage of bio iterator helpers Date: Tue, 13 Nov 2018 23:15:02 +0800 Message-Id: <20181113151505.15498-17-ming.lei@redhat.com> In-Reply-To: <20181113151505.15498-1-ming.lei@redhat.com> References: <20181113151505.15498-1-ming.lei@redhat.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.44]); Tue, 13 Nov 2018 15:16:47 +0000 (UTC) Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org 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. Cc: Christoph Hellwig Signed-off-by: Ming Lei --- Documentation/block/biovecs.txt | 26 ++++++++++++++++++++++++++ 1 file changed, 26 insertions(+) diff --git a/Documentation/block/biovecs.txt b/Documentation/block/biovecs.txt index 25689584e6e0..bfafb70d0d9e 100644 --- a/Documentation/block/biovecs.txt +++ b/Documentation/block/biovecs.txt @@ -117,3 +117,29 @@ 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, and usually they are used by filesystem code, and driver +shouldn't use them because bio may have been split before they got to 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 bvec, and the local +variable of 'struct bio_vec' or the reference records single-page IO +vector during the itearation: + + bio_for_each_segment() + bio_for_each_segment_all() + +* The following helper iterates over multi-page bvec, and each bvec may +include multiple physically contiguous pages, and the local variable of +'struct bio_vec' or the reference records multi-page IO vector during the +itearation: + + bio_for_each_bvec() -- 2.9.5