linux-kernel - Re: [PATCH v4 9/9] ovl: Allow case-insensitive lookup

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Message-ID: <CAOQ4uxjbCN6NGmDECFRKK_1Auq7RTfT+ZmVfVxgatMVav1EfAA@mail.gmail.com>
Date: Thu, 14 Aug 2025 10:44:51 +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 v4 9/9] ovl: Allow case-insensitive lookup

This last commit title should be like the title you gave patch 1:

ovl: Support mounting case-insensitive enabled layers

Because this is the commit that de-facto enabled the feature,
which is why I also asked to move the ovl_dentry_weird() change to this commit.

On Thu, Aug 14, 2025 at 12:37 AM André Almeida <andrealmeid@...lia.com> wrote:
>
> Drop the restriction for casefold dentries lookup to enable support for
> case-insensitive filesystems in overlayfs.
>
> Support case-insensitive filesystems

This is a problematic terminology
Please use the word "layers" instead of "filesystems" because casefolding is
not enabled at  the filesystem level. Could also say "subtrees"

Same for the rest of the commit messages, e.g.

"ovl: Prepare for mounting case-insensitive enabled layers"


Thanks,
Amir.


> with the condition that they should
> be uniformly enabled across the stack and the layers (i.e. if the root
> mount dir has casefold enabled, so should all the dirs bellow for every
> layer).
>
> Signed-off-by: André Almeida <andrealmeid@...lia.com>
> ---
> Changes from v3:
> - New patch, splited from the patch that creates ofs->casefold
> ---
>  fs/overlayfs/namei.c | 17 +++++++++--------
>  1 file changed, 9 insertions(+), 8 deletions(-)
>
> diff --git a/fs/overlayfs/namei.c b/fs/overlayfs/namei.c
> index 76d6248b625e7c58e09685e421aef616aadea40a..e93bcc5727bcafdc18a499b47a7609fd41ecaec8 100644
> --- a/fs/overlayfs/namei.c
> +++ b/fs/overlayfs/namei.c
> @@ -239,13 +239,14 @@ static int ovl_lookup_single(struct dentry *base, struct ovl_lookup_data *d,
>         char val;
>
>         /*
> -        * We allow filesystems that are case-folding capable but deny composing
> -        * ovl stack from case-folded directories. If someone has enabled case
> -        * folding on a directory on underlying layer, the warranty of the ovl
> -        * stack is voided.
> +        * We allow filesystems that are case-folding capable as long as the
> +        * layers are consistently enabled in the stack, enabled for every dir
> +        * or disabled in all dirs. If someone has modified case folding on a
> +        * directory on underlying layer, the warranty of the ovl stack is
> +        * voided.
>          */
> -       if (ovl_dentry_casefolded(base)) {
> -               warn = "case folded parent";
> +       if (ofs->casefold != ovl_dentry_casefolded(base)) {
> +               warn = "parent wrong casefold";
>                 err = -ESTALE;
>                 goto out_warn;
>         }
> @@ -259,8 +260,8 @@ static int ovl_lookup_single(struct dentry *base, struct ovl_lookup_data *d,
>                 goto out_err;
>         }
>
> -       if (ovl_dentry_casefolded(this)) {
> -               warn = "case folded child";
> +       if (ofs->casefold != ovl_dentry_casefolded(this)) {
> +               warn = "child wrong casefold";
>                 err = -EREMOTE;
>                 goto out_warn;
>         }
>
> --
> 2.50.1
>