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([2404:7a87:83e0:f800:fc6b:54b0:c37:7155]) by smtp.gmail.com with ESMTPSA id i128sm5158752pfe.74.2020.07.10.00.36.36 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 10 Jul 2020 00:36:38 -0700 (PDT) Subject: Re: [PATCH v3] exfat: remove EXFAT_SB_DIRTY flag To: Sungjong Seo Cc: kohada.tetsuhiro@dc.mitsubishielectric.co.jp, mori.takahiro@ab.mitsubishielectric.co.jp, motai.hirotaka@aj.mitsubishielectric.co.jp, 'Namjae Jeon' , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org References: <20200616021808.5222-1-kohada.t2@gmail.com> <414101d64477$ccb661f0$662325d0$@samsung.com> <500801d64572$0bdd2940$23977bc0$@samsung.com> From: Tetsuhiro Kohada Message-ID: Date: Fri, 10 Jul 2020 16:36:28 +0900 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <500801d64572$0bdd2940$23977bc0$@samsung.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2020/06/18 22:11, Sungjong Seo wrote: >> BTW >> Even with this patch applied, VOL_DIRTY remains until synced in the above >> case. >> It's not easy to reproduce as rmdir, but I'll try to fix it in the future. > > I think it's not a problem not to clear VOL_DIRTY under real errors, > because VOL_DIRTY is just like a hint to note that write was not finished clearly. > > If you mean there are more situation like ENOTEMPTY you mentioned, > please make new patch to fix them. When should VOL_DIRTY be cleared? The current behavior is ... Case of mkdir, rmdir, rename: - set VOL_DIRTY before operation - set VOL_CLEAN after operating. In async mode, it is actually written to the media after 30 seconds. Case of cp, touch: - set VOL_DIRTY before operation - however, VOL_CLEAN is not called in this context. VOL_CLEAN will call by sync_fs or unmount. I added VOL_CLEAN in last of __exfat_write_inode() and exfat_map_cluster(). As a result, VOL_DIRTY is cleared with cp and touch. However, when copying a many files ... - Async mode: VOL_DIRTY is written to the media twice every 30 seconds. - Sync mode: Of course, VOL_DIRTY and VOL_CLEAN to the media for each file. Frequent writing VOL_DIRTY and VOL_CLEAN increases the risk of boot-sector curruption. If the boot-sector corrupted, it causes the following serious problems on some OSs. - misjudge as unformatted - can't judge as exfat - can't repair I want to minimize boot sector writes, to reduce these risk. I looked vfat/udf implementation, which manages similar dirty information on linux, and found that they ware mark-dirty at mount and cleared at unmount. Here are some ways to clear VOL_DIRTY. (A) VOL_CLEAN after every write operation. :-) Ejectable at any time after a write operation. :-( Many times write to Boot-sector. (B) dirty at mount, clear at unmount (same as vfat/udf) :-) Write to boot-sector twice. :-( It remains dirty unless unmounted. :-( Write to boot-sector even if there is no write operation.　 (C) dirty on first write operation, clear on unmount :-) Writing to boot-sector is minimal. :-) Will not write to the boot-sector if there is no write operation. :-( It remains dirty unless unmounted. (D) dirty on first write operation, clear on sync-fs/unmount :-) Writing to boot-sector can be reduced. :-) Will not write to the boot-sector if there is no write operation. :-) sync-fs makes it clean and ejectable immidiately. :-( It remains dirty unless sync-fs or unmount. :-( Frequent sync-fs will increases writes to boot-sector. I think it should be (C) or(D). What do you think? BR --- Tetsuhiro Kohada