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=-20.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 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 1B304C433E0 for ; Thu, 25 Feb 2021 01:37:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id CC35F64EC4 for ; Thu, 25 Feb 2021 01:37:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235101AbhBYBhw (ORCPT ); Wed, 24 Feb 2021 20:37:52 -0500 Received: from szxga07-in.huawei.com ([45.249.212.35]:13374 "EHLO szxga07-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233895AbhBYBht (ORCPT ); Wed, 24 Feb 2021 20:37:49 -0500 Received: from DGGEMS409-HUB.china.huawei.com (unknown [172.30.72.58]) by szxga07-in.huawei.com (SkyGuard) with ESMTP id 4DmFjH2QB8z7q1b; Thu, 25 Feb 2021 09:35:31 +0800 (CST) Received: from [10.136.110.154] (10.136.110.154) by smtp.huawei.com (10.3.19.209) with Microsoft SMTP Server (TLS) id 14.3.498.0; Thu, 25 Feb 2021 09:37:06 +0800 Subject: Re: [f2fs-dev] [PATCH][next] f2fs: Replace one-element array with flexible-array member To: "Gustavo A. R. Silva" , Jaegeuk Kim CC: Chao Yu , , , References: <20210224190313.GA144040@embeddedor> From: Chao Yu Message-ID: Date: Thu, 25 Feb 2021 09:37:05 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <20210224190313.GA144040@embeddedor> Content-Type: text/plain; charset="utf-8"; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit X-Originating-IP: [10.136.110.154] X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello, Gustavo, On 2021/2/25 3:03, Gustavo A. R. Silva wrote: > There is a regular need in the kernel to provide a way to declare having > a dynamically sized set of trailing elements in a structure. Kernel code > should always use “flexible array members”[1] for these cases. The older > style of one-element or zero-length arrays should no longer be used[2]. I proposal to do the similar cleanup, and I've no objection on doing this. https://lore.kernel.org/patchwork/patch/869440/ Let's ask for Jaegeuk' opinion. > > Refactor the code according to the use of a flexible-array member in > struct f2fs_checkpoint, instead of a one-element arrays. > > Notice that a temporary pointer to void '*tmp_ptr' was used in order to > fix the following errors when using a flexible array instead of a one > element array in struct f2fs_checkpoint: > > CC [M] fs/f2fs/dir.o > In file included from fs/f2fs/dir.c:13: > fs/f2fs/f2fs.h: In function ‘__bitmap_ptr’: > fs/f2fs/f2fs.h:2227:40: error: invalid use of flexible array member > 2227 | return &ckpt->sit_nat_version_bitmap + offset + sizeof(__le32); > | ^ > fs/f2fs/f2fs.h:2227:49: error: invalid use of flexible array member > 2227 | return &ckpt->sit_nat_version_bitmap + offset + sizeof(__le32); > | ^ > fs/f2fs/f2fs.h:2238:40: error: invalid use of flexible array member > 2238 | return &ckpt->sit_nat_version_bitmap + offset; > | ^ > make[2]: *** [scripts/Makefile.build:287: fs/f2fs/dir.o] Error 1 > make[1]: *** [scripts/Makefile.build:530: fs/f2fs] Error 2 > make: *** [Makefile:1819: fs] Error 2 > > [1] https://en.wikipedia.org/wiki/Flexible_array_member > [2] https://www.kernel.org/doc/html/v5.9/process/deprecated.html#zero-length-and-one-element-arrays > > Link: https://github.com/KSPP/linux/issues/79 > Build-tested-by: kernel test robot > Link: https://lore.kernel.org/lkml/603647e4.DeEFbl4eqljuwAUe%25lkp@intel.com/ > Signed-off-by: Gustavo A. R. Silva > --- > fs/f2fs/f2fs.h | 5 +++-- > include/linux/f2fs_fs.h | 2 +- > 2 files changed, 4 insertions(+), 3 deletions(-) > > diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h > index e2d302ae3a46..3f5cb097c30f 100644 > --- a/fs/f2fs/f2fs.h > +++ b/fs/f2fs/f2fs.h > @@ -2215,6 +2215,7 @@ static inline block_t __cp_payload(struct f2fs_sb_info *sbi) > static inline void *__bitmap_ptr(struct f2fs_sb_info *sbi, int flag) > { > struct f2fs_checkpoint *ckpt = F2FS_CKPT(sbi); > + void *tmp_ptr = &ckpt->sit_nat_version_bitmap; > int offset; > > if (is_set_ckpt_flags(sbi, CP_LARGE_NAT_BITMAP_FLAG)) { > @@ -2224,7 +2225,7 @@ static inline void *__bitmap_ptr(struct f2fs_sb_info *sbi, int flag) > * if large_nat_bitmap feature is enabled, leave checksum > * protection for all nat/sit bitmaps. > */ > - return &ckpt->sit_nat_version_bitmap + offset + sizeof(__le32); > + return tmp_ptr + offset + sizeof(__le32); > } > > if (__cp_payload(sbi) > 0) { > @@ -2235,7 +2236,7 @@ static inline void *__bitmap_ptr(struct f2fs_sb_info *sbi, int flag) > } else { > offset = (flag == NAT_BITMAP) ? > le32_to_cpu(ckpt->sit_ver_bitmap_bytesize) : 0; > - return &ckpt->sit_nat_version_bitmap + offset; > + return tmp_ptr + offset; > } > } > > diff --git a/include/linux/f2fs_fs.h b/include/linux/f2fs_fs.h > index c6cc0a566ef5..5487a80617a3 100644 > --- a/include/linux/f2fs_fs.h > +++ b/include/linux/f2fs_fs.h > @@ -168,7 +168,7 @@ struct f2fs_checkpoint { > unsigned char alloc_type[MAX_ACTIVE_LOGS]; > > /* SIT and NAT version bitmap */ > - unsigned char sit_nat_version_bitmap[1]; > + unsigned char sit_nat_version_bitmap[]; > } __packed; > > #define CP_CHKSUM_OFFSET 4092 /* default chksum offset in checkpoint */ >