linux-kernel - Re: [PATCH -next] powerpc/powernv: Fix debugfs_simple

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Message-ID: <87va6c268q.fsf@concordia.ellerman.id.au>
Date:   Mon, 08 Oct 2018 19:27:17 +1100
From:   Michael Ellerman <mpe@...erman.id.au>
To:     YueHaibing <yuehaibing@...wei.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        David Hildenbrand <david@...hat.com>,
        Michael Neuling <mikey@...ling.org>,
        Balbir Singh <bsingharora@...il.com>,
        Rashmica Gupta <rashmica.g@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Pavel Tatashin <pavel.tatashin@...rosoft.com>,
        Stephen Rothwell <sfr@...b.auug.org.au>
Cc:     YueHaibing <yuehaibing@...wei.com>, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: Re: [PATCH -next] powerpc/powernv: Fix debugfs_simple_attr.cocci warnings

YueHaibing <yuehaibing@...wei.com> writes:
> Use DEFINE_DEBUGFS_ATTRIBUTE rather than DEFINE_SIMPLE_ATTRIBUTE
> for debugfs files.
>
> Semantic patch information:
> Rationale: DEFINE_SIMPLE_ATTRIBUTE + debugfs_create_file()
> imposes some significant overhead as compared to
> DEFINE_DEBUGFS_ATTRIBUTE + debugfs_create_file_unsafe().

Sorry this isn't detailed enough for me to actually understand the
pros/cons of this patch.

Perhaps I'm expected to know it, but I don't.

I had a look at what each macro produces and it wasn't obvious to me
what the benefit is.

cheers

> Generated by: scripts/coccinelle/api/debugfs/debugfs_simple_attr.cocci
>
> Signed-off-by: YueHaibing <yuehaibing@...wei.com>
> ---
>  arch/powerpc/platforms/powernv/memtrace.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/arch/powerpc/platforms/powernv/memtrace.c b/arch/powerpc/platforms/powernv/memtrace.c
> index 84d038e..0cb6548 100644
> --- a/arch/powerpc/platforms/powernv/memtrace.c
> +++ b/arch/powerpc/platforms/powernv/memtrace.c
> @@ -311,8 +311,8 @@ static int memtrace_enable_get(void *data, u64 *val)
>  	return 0;
>  }
>  
> -DEFINE_SIMPLE_ATTRIBUTE(memtrace_init_fops, memtrace_enable_get,
> -					memtrace_enable_set, "0x%016llx\n");
> +DEFINE_DEBUGFS_ATTRIBUTE(memtrace_init_fops, memtrace_enable_get,
> +			 memtrace_enable_set, "0x%016llx\n");
>  
>  static int memtrace_init(void)
>  {
> @@ -321,8 +321,8 @@ static int memtrace_init(void)
>  	if (!memtrace_debugfs_dir)
>  		return -1;
>  
> -	debugfs_create_file("enable", 0600, memtrace_debugfs_dir,
> -			    NULL, &memtrace_init_fops);
> +	debugfs_create_file_unsafe("enable", 0600, memtrace_debugfs_dir, NULL,
> +				   &memtrace_init_fops);
>  
>  	return 0;
>  }