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	Mon, 05 May 2025 16:27:34 +0000
Date: Mon, 5 May 2025 17:27:34 +0100
From: Matthew Wilcox <willy@infradead.org>
To: Miklos Szeredi <mszeredi@redhat.com>
Cc: linux-fsdevel@vger.kernel.org, linux-unionfs@vger.kernel.org,
	=?iso-8859-1?Q?Andr=E9?= Almeida <andrealmeid@igalia.com>,
	John Schoenick <johns@valvesoftware.com>
Subject: Re: [PATCH] vfs: change 'struct file *' argument to 'const struct
 file *' where possible
Message-ID: <aBjm9khhIBOUTFcV@casper.infradead.org>
References: <20250505154149.301235-1-mszeredi@redhat.com>
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In-Reply-To: <20250505154149.301235-1-mszeredi@redhat.com>

On Mon, May 05, 2025 at 05:41:47PM +0200, Miklos Szeredi wrote:
> -static inline struct backing_file *backing_file(struct file *f)
> +#define backing_file(f) container_of(f, struct backing_file, file)
> +
> +struct path *backing_file_user_path(struct file *f)
>  {
> -	return container_of(f, struct backing_file, file);
> +	return &backing_file(f)->user_path;
>  }
>  
> -struct path *backing_file_user_path(struct file *f)
> +const struct path *backing_file_user_path_c(const struct file *f)
>  {
>  	return &backing_file(f)->user_path;
>  }
> -EXPORT_SYMBOL_GPL(backing_file_user_path);
> +EXPORT_SYMBOL_GPL(backing_file_user_path_c);

May I suggest:

#define backing_file_user_path(f)	(_Generic((f),		\
	const struct file *:	(const struct path *)&backing_file(f)->user_path,  \
	struct file *:		(struct path *)&backing_file(f)->user_path)))

It's the same technique we use for page_folio() so it's quite well
tested.