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

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Date: Wed, 22 Nov 2023 16:18:56 -0800
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: Al Viro <viro@...iv.linux.org.uk>
Cc: Christian Brauner <brauner@...nel.org>, Gabriel Krisman Bertazi <krisman@...e.de>, 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

On Wed, 22 Nov 2023 at 13:19, Al Viro <viro@...iv.linux.org.uk> wrote:
>
> The serious gap, AFAICS, is the interplay with open-by-fhandle.

So I'm obviously not a fan of igncase filesystems, but I don't think
this series actually changes any of that.

> It's not unfixable, but we need to figure out what to do when
> lookup runs into a disconnected directory alias.  d_splice_alias()
> will move it in place, all right, but any state ->lookup() has
> hung off the dentry that had been passed to it will be lost.

I guess this migth be about the new DCACHE_CASEFOLDED_NAME bit.

At least for now, that is only used by generic_ci_d_revalidate() for
negative dentries, so it shouldn't matter for that d_splice_alias()
that only does positive dentries. No?

Or is there something else you worry about?

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?

             Linus