Re: [PATCH 4/4] file: make struct fd_prepare const and kill its err field

[David Laight <david.laight.linux@gmail.com>]

On Thu, 17 Sep 2026 11:09:45 +0200
Christian Brauner <brauner@kernel.org> wrote:

> FD_PREPARE() releases the fd as soon as the file expression fails. The
> fd either holds the descriptor or the error. The separate field is
> redundant. Make fd and file plain members and struct fd_prepare simpler.
> 
> Callers of FD_PREPARE() get a const pointer to the guard. Simplify all
> users as they can now easily access the trivial struct.
> 
...
> @@ -191,35 +175,39 @@ static __always_inline struct fd_prepare __fd_prepare(int fd, struct file *file)
>   * was allocated. If fd_publish() was called the fd and file are
>   * published and cleanup becomes a nop.
>   *
> - * @_fdf: name of struct fd_prepare variable to define
> + * @_fdf: name of the const struct fd_prepare pointer to define
>   * @_fd_flags: flags for get_unused_fd_flags()
>   * @_file_owned: struct file to take ownership of (can be expression)
>   */
> -#define FD_PREPARE(_fdf, _fd_flags, _file_owned)			\
> -	struct fd_prepare _fdf __cleanup(__fd_prepare_cleanup) = ({	\
> +#define __FD_PREPARE(_guard, _fdf, _fd_flags, _file_owned)		\
> +	struct fd_prepare _guard __cleanup(__fd_prepare_cleanup) = ({	\
>  		int __fd = get_unused_fd_flags(_fd_flags);		\
>  		__fd_prepare(__fd, __fd < 0 ? NULL : (_file_owned));	\
> -	})
> +	});								\
> +	const struct fd_prepare *const _fdf = &_guard

Since the struct is only written by its initialiser, can't it just
be 'const' ?

David