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Date: Wed, 30 Sep 2020 13:01:47 +0900 From: Tetsuhiro Kohada <kohada.t2@...il.com> To: Sungjong Seo <sj1557.seo@...sung.com> Cc: kohada.tetsuhiro@...mitsubishielectric.co.jp, mori.takahiro@...mitsubishielectric.co.jp, motai.hirotaka@...mitsubishielectric.co.jp, 'Namjae Jeon' <namjae.jeon@...sung.com>, linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH 2/3] exfat: remove useless check in exfat_move_file() >>> It might check if the cluster numbers are same between source entry >>> and target directory. >> >> This checks if newdir is the move target itself. >> Example: >> mv /mnt/dir0 /mnt/dir0/foo >> >> However, this check is not enough. >> We need to check newdir and all ancestors. >> Example: >> mv /mnt/dir0 /mnt/dir0/dir1/foo >> mv /mnt/dir0 /mnt/dir0/dir1/dir2/foo >> ... >> >> This is probably a taboo for all layered filesystems. >> >> >>> Could you let me know what code you mentioned? >>> Or do you mean the codes on vfs? >> >> You can find in do_renameat2(). --- around 'fs/namei.c:4440' >> If the destination ancestors are itself, our driver will not be called. > > I think, of course, vfs has been doing that. > So that code is unnecessary in normal situations. > > That code comes from the old exfat implementation. It could be a remnant of another system. Once upon a time, I moved the dir to a descendant dir without implementing this check and it disappeared forever. linux-VFS fixed this issue immediately, but some systems still need to be checked by the driver itself. (ex.Windows-IFS) > And as far as I understand, it seems to check once more "the cluster number" > even though it comes through vfs so that it tries detecting abnormal of on-disk. > > Anyway, I agonized if it is really needed. > In conclusion, old code could be eliminated and your patch looks reasonable. It's easy to add, but it's really hard to remove the ancient code. BTW I have a question for you. Now, I'm trying to optimize exfat_get_dentry(). However, exfat_get_dentry() is used a lot, so the patch is also large. In such a case -Replace old implementation with new ones with a single patch. -Devide multiple patches in which old functions and new functions (ex. exfat_get_dentry2) coexist temporarily. And finally clean up. I understand that a small patch is desirable, but the latter has "two similar functions". Which is better for you to review the patch? BR --- Tetsuhiro Kohada <kohada.t2@...il.com>
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