linux-kernel - Re: [PATCH RFC v3 0/7] ovl: Enable support for casefold filesystems

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Message-ID: <CAOQ4uxj13iGDE-tz91BLpjOcJror77-pG4CkxQB18YDXX0kUkg@mail.gmail.com>
Date: Sat, 9 Aug 2025 18:08:02 +0200
From: Amir Goldstein <amir73il@...il.com>
To: André Almeida <andrealmeid@...lia.com>
Cc: Miklos Szeredi <miklos@...redi.hu>, Theodore Tso <tytso@....edu>, 
	Gabriel Krisman Bertazi <krisman@...nel.org>, linux-unionfs@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org, 
	Alexander Viro <viro@...iv.linux.org.uk>, Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>, 
	kernel-dev@...lia.com
Subject: Re: [PATCH RFC v3 0/7] ovl: Enable support for casefold filesystems

On Sat, Aug 9, 2025 at 11:17 AM Amir Goldstein <amir73il@...il.com> wrote:
>
> On Fri, Aug 8, 2025 at 10:59 PM André Almeida <andrealmeid@...lia.com> wrote:
> >
> > Hi all,
> >
> > We would like to support the usage of casefold filesystems with
> > overlayfs to be used with container tools. This use case requires a
> > simple setup, where every layer will have the same encoding setting
> > (i.e. Unicode version and flags), using one upper and one lower layer.
> >
> > * Implementation
> >
> > When merge layers, ovl uses a red-black tree to check if a given dentry
> > name from a lower layers already exists in the upper layer. For merging
> > case-insensitive names, we need to store then in tree casefolded.
> > However, when displaying to the user the dentry name, we need to respect
> > the name chosen when the file was created (e.g. Picture.PNG, instead of
> > picture.png). To achieve this, I create a new field for cache entries
> > that stores the casefolded names and a function ovl_strcmp() that uses
> > this name for searching the rb_tree. For composing the layer, ovl uses
> > the original name, keeping it consistency with whatever name the user
> > created.
> >
> > The rest of the patches are mostly for checking if casefold is being
> > consistently used across the layers and dropping the mount restrictions
> > that prevented case-insensitive filesystems to be mounted.
> >
> > Thanks for the feedback!
>
> Hi Andre,
>
> This v3 is getting close.
> Still some small details to fix.
> With v4, please include a link to fstest so I can test your work.
> I already had a draft for the casefold capable and disabled layers
> in 6.17 but I did not post it yet.
> Decide it would be better to test the final result after your work.
> I'd started to adapt the test to the expected behavior for 6.18,
> but it's just an untested draft for you to extend:
> https://github.com/amir73il/xfstests/commits/ovl-casefold/
>
> Please make sure that you run at least check -overlay -g overlay/quick
> sanity check for v4 and that you run check -g casefold,
> which should run the new generic test.
>

Also, please remove the RFC label for v4.
We are pass the point of RFC.

Thanks,
Amir.