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From: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
Date: Mon, 19 Jul 2021 19:37:37 +0200
Message-ID: <CANiq72=tm_ERbkG1jyWwuyJqzgA9M8Hd7rCQ-tJ7Tf_E-v2wgA@mail.gmail.com>
Subject: Re: [TECH TOPIC] Rust for Linux
To: Arnd Bergmann <arnd@arndb.de>
Cc: Wedson Almeida Filho <wedsonaf@google.com>, Linus Walleij <linus.walleij@linaro.org>, 
	Greg KH <greg@kroah.com>, Bartosz Golaszewski <bgolaszewski@baylibre.com>, 
	Kees Cook <keescook@chromium.org>, Jan Kara <jack@suse.cz>, 
	James Bottomley <James.Bottomley@hansenpartnership.com>, 
	Julia Lawall <julia.lawall@inria.fr>, 
	Laurent Pinchart <laurent.pinchart@ideasonboard.com>, Roland Dreier <roland@kernel.org>, 
	ksummit@lists.linux.dev, Viresh Kumar <viresh.kumar@linaro.org>
Content-Type: text/plain; charset="UTF-8"

On Mon, Jul 19, 2021 at 4:02 PM Arnd Bergmann <arnd@arndb.de> wrote:
>
> - What is the mechanism behind power::Operations that replaces the
>    #ifdef CONFIG_PM of the C version? Will the rust compiler just drop
>    the dead code when CONFIG_PM is disabled?

We support conditional compilation with the kernel configuration, e.g.:

    #[cfg(CONFIG_X)]      // `CONFIG_X` is enabled (`y` or `m`)
    #[cfg(CONFIG_X="y")]  // `CONFIG_X` is enabled as a built-in (`y`)
    #[cfg(CONFIG_X="m")]  // `CONFIG_X` is enabled as a module   (`m`)
    #[cfg(not(CONFIG_X))] // `CONFIG_X` is disabled

One can use it, like in C, to fully remove any item as a user, to make
an implementation a noop (so that callers do not need to care), etc.

Cheers,
Miguel