linux-kernel - Re: [PATCH v5 9/9] ovl: Support mounting case-insensitive enabled layers

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Message-ID: <CAOQ4uxiERO5g0RoG3s13jV6OfoqySt4pXfvOTPy+rbLwvfjOdQ@mail.gmail.com>
Date: Thu, 14 Aug 2025 20:48:02 +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 v5 9/9] ovl: Support mounting case-insensitive enabled layers

On Thu, Aug 14, 2025 at 7:22 PM André Almeida <andrealmeid@...lia.com> wrote:
>
> Drop the restriction for casefold dentries lookup to enable support for
> case-insensitive layers in overlayfs.
>
> Support case-insensitive layers with the condition that they should be
> uniformly enabled across the stack and (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>
Reviewed-by: Amir Goldstein <amir73il@...il.com>

> ---
> Changes from v4:
> - Move the dentry_weird relaxation to this patch
> - Reword the commit title and message
>
> Changes from v3:
> - New patch, splited from the patch that creates ofs->casefold
> ---
>  fs/overlayfs/namei.c | 17 +++++++++--------
>  fs/overlayfs/util.c  |  8 ++++----
>  2 files changed, 13 insertions(+), 12 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;
>         }
> diff --git a/fs/overlayfs/util.c b/fs/overlayfs/util.c
> index a33115e7384c129c543746326642813add63f060..7a6ee058568283453350153c1720c35e11ad4d1b 100644
> --- a/fs/overlayfs/util.c
> +++ b/fs/overlayfs/util.c
> @@ -210,11 +210,11 @@ bool ovl_dentry_weird(struct dentry *dentry)
>                 return true;
>
>         /*
> -        * Allow filesystems that are case-folding capable but deny composing
> -        * ovl stack from case-folded directories.
> +        * Exceptionally for casefold dentries, we accept that they have their
> +        * own hash and compare operations
>          */
> -       if (sb_has_encoding(dentry->d_sb))
> -               return IS_CASEFOLDED(d_inode(dentry));
> +       if (ovl_dentry_casefolded(dentry))
> +               return false;
>
>         return dentry->d_flags & (DCACHE_OP_HASH | DCACHE_OP_COMPARE);
>  }
>
> --
> 2.50.1
>