linux-kernel - Re: Unicode conversion issue

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Message-ID: <Z1oJ7PgRvLyctn0X@google.com>
Date: Wed, 11 Dec 2024 21:53:48 +0000
From: Jaegeuk Kim <jaegeuk@...nel.org>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Gabriel Krisman Bertazi <krisman@...e.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"hanqi@...o.com" <hanqi@...o.com>, Theodore Ts'o <tytso@....edu>
Subject: Re: Unicode conversion issue

On 12/11, Linus Torvalds wrote:
> On Wed, 11 Dec 2024 at 13:11, Gabriel Krisman Bertazi <krisman@...e.de> wrote:
> >
> > This solves it for directories with inlined dirents
> > (FI_INLINE_DENTRY). but for large directories, we use fname->hash to
> > find the right block to start the search.
> 
> Grr. Dammit, the hash should always have been the original hash of the
> original actual case-preserving entry.
> 
> Oh well. I'll continue to just absolutely hate case-folding, because
> while I suspect that it *could* be done correctly, I have yet to ever
> actually see any filesystem that did so.

Casefolding supports f2fs and ext4 per Android request, and only f2fs
constructs hash-based directory structure. If we use hash of the
case-preserving entry, we had no easy solution to distinguish file_A and file_a.

One possible way might be searching only filename sequentially through
the entire dentry list, if we fail to find the new encoded entry. But, it may
need a huge surgery to make it work.

> 
>             Linus