linux-kernel - Re: [PATCH] x86/platform/uv: avoid unused variable warning

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Date:   Thu, 12 Dec 2019 07:16:07 -0800
From:   Mike Travis <mike.travis@....com>
To:     Christoph Hellwig <hch@...radead.org>,
        Arnd Bergmann <arnd@...db.de>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, Steve Wahl <steve.wahl@....com>,
        Dimitri Sivanich <dimitri.sivanich@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Hedi Berriche <hedi.berriche@....com>,
        Justin Ernst <justin.ernst@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Russ Anderson <russ.anderson@....com>,
        Anshuman Khandual <anshuman.khandual@....com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86/platform/uv: avoid unused variable warning




On 12/12/2019 6:54 AM, Christoph Hellwig wrote:
> Instead of that maybe_unused mess please just use good old ifdefs.
> 
>>   	if (hubless)
>> -		proc_version_fops.open = proc_hubless_open;
>> +		proc_create_single("hubless", 0, pde, proc_hubless_show);
>>   	else
>> -		proc_version_fops.open = proc_hubbed_open;
>> +		proc_create_single("hubbed", 0, pde, proc_hubbed_show);
>>   }
> 
> Or someone could figure out what happens if we turn the
> proc_create_single stub into an inline function instead of the
> define.  That makes it used at a syntactic level, the big question is
> if the compiler is smart enough to optimize away the unused callback
> still.
> 

Yes, if CONFIG_PROC_FS is undefined, then this whole section can be 
removed since it's sole purpose is to set up the /proc/ interface. 
Something like this should suffice:

> ---
>  arch/x86/kernel/apic/x2apic_uv_x.c |    9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> --- linux.orig/arch/x86/kernel/apic/x2apic_uv_x.c
> +++ linux/arch/x86/kernel/apic/x2apic_uv_x.c
> @@ -1533,6 +1533,7 @@ static void check_efi_reboot(void)
>                 reboot_type = BOOT_ACPI;
>  }
> 
> +#ifdef CONFIG_PROC_FS
>  /* Setup user proc fs files */
>  static int proc_hubbed_show(struct seq_file *file, void *data)
>  {
> @@ -1595,6 +1596,14 @@ static __init void uv_setup_proc_files(i
>                 proc_version_fops.open = proc_hubbed_open;
>  }
> 
> +#else /* !CONFIG_PROC_FS */
> +
> +static __init void uv_setup_proc_files(int hubless)
> +{
> +}
> +
> +#endif /* !CONFIG_PROC_FS */
> +
>  /* Initialize UV hubless systems */
>  static __init int uv_system_init_hubless(void)
>  {