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Date:   Fri, 16 Apr 2021 17:35:08 +0000
From:   Al Viro <viro@zeniv.linux.org.uk>
To:     Chung-Chiang Cheng <shepjeng@gmail.com>
Cc:     christian.brauner@ubuntu.com, linux-fsdevel@vger.kernel.org,
        linux-kernel@vger.kernel.org, cccheng@synology.com
Subject: Re: [PATCH] hfsplus: prevent negative dentries when casefolded
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References: <20210416172012.8667-1-cccheng@synology.com>
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On Sat, Apr 17, 2021 at 01:20:12AM +0800, Chung-Chiang Cheng wrote:
> hfsplus uses the case-insensitive filenames by default, but VFS negative
> dentries are incompatible with case-insensitive. For example, the
> following instructions will get a cached filename 'aaa' which isn't
> expected. There is no such problem in macOS.

Look into the way vfat et.al. are dealing with that (see their
->d_revalidate()).