linux-ext4 - Re: [f2fs-dev] [PATCH v6 0/9] Support negative dentries on case-insensitive ext4 and f2fs

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Date: Thu, 23 Nov 2023 10:57:22 -0500
From: Gabriel Krisman Bertazi <gabriel@...sman.be>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Al Viro <viro@...iv.linux.org.uk>,  Christian Brauner
 <brauner@...nel.org>,  tytso@....edu,
  linux-f2fs-devel@...ts.sourceforge.net,  ebiggers@...nel.org,
  linux-fsdevel@...r.kernel.org,  jaegeuk@...nel.org,
  linux-ext4@...r.kernel.org
Subject: Re: [f2fs-dev] [PATCH v6 0/9] Support negative dentries on
 case-insensitive ext4 and f2fs

Linus Torvalds <torvalds@...ux-foundation.org> writes:

> Side note: Gabriel, as things are now, instead of that
>
>         if (!d_is_casefolded_name(dentry))
>                 return 0;
>
> in generic_ci_d_revalidate(), I would suggest that any time a
> directory is turned into a case-folded one, you'd just walk all the
> dentries for that directory and invalidate negative ones at that
> point. Or was there some reason I missed that made it a good idea to
> do it at run-time after-the-fact?
>

The problem I found with that approach, which I originally tried, was
preventing concurrent lookups from racing with the invalidation and
creating more 'case-sensitive' negative dentries.  Did I miss a way to
synchronize with concurrent lookups of the children of the dentry?  We
can trivially ensure the dentry doesn't have positive children by
holding the parent lock, but that doesn't protect from concurrent
lookups creating negative dentries, as far as I understand.

-- 
Gabriel Krisman Bertazi