linux-kernel - Re: [PATCH v4 4/9] fs: Create sb_same

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Message-ID: <CAOQ4uxj4AvR851vZ7d_QZm1Grg2aa0hefP0-bywRXamHFXyP5A@mail.gmail.com>
Date: Thu, 14 Aug 2025 14:19:18 +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 4/9] fs: Create sb_same_encoding() helper

On Thu, Aug 14, 2025 at 12:37 AM André Almeida <andrealmeid@...lia.com> wrote:
>
> For cases where a file lookup can look in different filesystems (like in
> overlayfs), both super blocks must have the same encoding and the same
> flags. To help with that, create a sb_same_encoding() function.
>
> Reviewed-by: Amir Goldstein <amir73il@...il.com>
> Signed-off-by: André Almeida <andrealmeid@...lia.com>

please reorder vfs patches before ovl patches

> Changes from v3:
> - Improve wording
>
> Changes from v2:
> - Simplify the code. Instead of `if (cond) return true`, just do `return
>   cond`;
> ---
>  include/linux/fs.h | 18 ++++++++++++++++++
>  1 file changed, 18 insertions(+)
>
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 20102d81e18a59d5daaed06855d1f168979b4fa7..64d24e89bc5593915158b40f0442e6d8ef3d968d 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -3753,6 +3753,24 @@ static inline bool sb_has_encoding(const struct super_block *sb)
>         return !!sb_encoding(sb);
>  }
>
> +/*
> + * Compare if two super blocks have the same encoding and flags
> + */
> +static inline bool sb_same_encoding(const struct super_block *sb1,
> +                                   const struct super_block *sb2)
> +{
> +#if IS_ENABLED(CONFIG_UNICODE)
> +       if (sb1->s_encoding == sb2->s_encoding)
> +               return true;
> +
> +       return (sb1->s_encoding && sb2->s_encoding &&
> +              (sb1->s_encoding->version == sb2->s_encoding->version) &&
> +              (sb1->s_encoding_flags == sb2->s_encoding_flags));
> +#else
> +       return true;
> +#endif
> +}
> +
>  int may_setattr(struct mnt_idmap *idmap, struct inode *inode,
>                 unsigned int ia_valid);
>  int setattr_prepare(struct mnt_idmap *, struct dentry *, struct iattr *);
>
> --
> 2.50.1
>