linux-kernel - Re: [Linux-eng] [RFC 0/3] Abstract empty functions with STUB

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Date:   Fri, 18 Jan 2019 16:37:36 +0000
From:   Russell King - ARM Linux admin <linux@...linux.org.uk>
To:     Andrew Murray <andrew.murray@....com>
Cc:     Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Arnd Bergmann <arnd@...db.de>,
        Kees Cook <keescook@...omium.org>,
        Andrew Morton <akpm@...ux-foundation.org>, rjw@...ysocki.net,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        linux-kernel@...r.kernel.org, Steven Price <Steven.Price@....com>,
        Grant Likely <Grant.Likely@....com>,
        Dave P Martin <Dave.Martin@....com>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [Linux-eng] [RFC 0/3] Abstract empty functions with STUB_UNLESS
 macro

On Fri, Jan 18, 2019 at 04:00:27PM +0000, Andrew Murray wrote:
> A common pattern found in header files is a function declaration dependent
> on a CONFIG_ option being enabled, followed by an empty function for when
> that option isn't enabled. This boilerplate code can often take up a lot
> of space and impact code readability.
> 
> This series introduces a STUB_UNLESS macro that simplifies header files as
> follows:
> 
> STUB_UNLESS(CONFIG_FOO, [body], prototype)

Can you explain the desire to make the second argument optional,
rather than having the mandatory arguments first and the optional body
last?  It will mean more lines at each site, but I don't think that's
a bad thing:

STUB_UNLESS(CONFIG_HAVE_HW_BREAKPOINT,
void hw_breakpoint_thread_switch(struct task_struct *next));

STUB_UNLESS(CONFIG_CPU_FREQ,
struct cpufreq_policy *cpufreq_cpu_get_raw(unsigned int cpu), return NULL);

or:

STUB_UNLESS(CONFIG_CPU_FREQ,
struct cpufreq_policy *cpufreq_cpu_get_raw(unsigned int cpu),
	return NULL);

Seems to be more readable in terms of the flow.

-- 
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