linux-kernel - Re: [PATCH v6 5/9] ovl: Ensure that all layers have the same encoding

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Message-ID: <871poz647l.fsf@mailhost.krisman.be>
Date: Mon, 25 Aug 2025 07:17:02 -0400
From: Gabriel Krisman Bertazi <gabriel@...sman.be>
To: André Almeida <andrealmeid@...lia.com>
Cc: Miklos Szeredi <miklos@...redi.hu>,  Amir Goldstein
 <amir73il@...il.com>,  Theodore Tso <tytso@....edu>,
  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 v6 5/9] ovl: Ensure that all layers have the same encoding

André Almeida <andrealmeid@...lia.com> writes:

> When merging layers from different filesystems with casefold enabled,
> all layers should use the same encoding version and have the same flags
> to avoid any kind of incompatibility issues.
>
> Also, set the encoding and the encoding flags for the ovl super block as
> the same as used by the first valid layer.
>
> Reviewed-by: Amir Goldstein <amir73il@...il.com>
> Signed-off-by: André Almeida <andrealmeid@...lia.com>
> ---
>  fs/overlayfs/super.c | 25 +++++++++++++++++++++++++
>  1 file changed, 25 insertions(+)
>
> diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
> index df85a76597e910d00323018f1d2cd720c5db921d..b1dbd3c79961094d00c7f99cc622e515d544d22f 100644
> --- a/fs/overlayfs/super.c
> +++ b/fs/overlayfs/super.c
> @@ -991,6 +991,18 @@ static int ovl_get_data_fsid(struct ovl_fs *ofs)
>  	return ofs->numfs;
>  }
>  
> +/*
> + * Set the ovl sb encoding as the same one used by the first layer
> + */
> +static void ovl_set_encoding(struct super_block *sb, struct super_block *fs_sb)
> +{
> +#if IS_ENABLED(CONFIG_UNICODE)
> +	if (sb_has_encoding(fs_sb)) {
> +		sb->s_encoding = fs_sb->s_encoding;
> +		sb->s_encoding_flags = fs_sb->s_encoding_flags;
> +	}
> +#endif
> +}
>  
>  static int ovl_get_layers(struct super_block *sb, struct ovl_fs *ofs,
>  			  struct ovl_fs_context *ctx, struct ovl_layer *layers)
> @@ -1024,6 +1036,9 @@ static int ovl_get_layers(struct super_block *sb, struct ovl_fs *ofs,
>  	if (ovl_upper_mnt(ofs)) {
>  		ofs->fs[0].sb = ovl_upper_mnt(ofs)->mnt_sb;
>  		ofs->fs[0].is_lower = false;
> +
> +		if (ofs->casefold)
> +			ovl_set_encoding(sb, ofs->fs[0].sb);
>  	}
>  
>  	nr_merged_lower = ctx->nr - ctx->nr_data;
> @@ -1083,6 +1098,16 @@ static int ovl_get_layers(struct super_block *sb, struct ovl_fs *ofs,
>  		l->name = NULL;
>  		ofs->numlayer++;
>  		ofs->fs[fsid].is_lower = true;
> +
> +		if (ofs->casefold) {
> +			if (!ovl_upper_mnt(ofs) && !sb_has_encoding(sb))
> +				ovl_set_encoding(sb, ofs->fs[fsid].sb);
> +
> +			if (!sb_has_encoding(sb) || !sb_same_encoding(sb, mnt->mnt_sb)) {

Minor nit, but isn't the sb_has_encoding()  check redundant here?  sb_same_encoding
will check the sb->encoding matches the mnt_sb already.

> +				pr_err("all layers must have the same encoding\n");
> +				return -EINVAL;
> +			}
> +		}
>  	}
>
>  	/*

-- 
Gabriel Krisman Bertazi