linux-kernel - Re: [PATCH v2 0/3] sysfs: constify bin_attribute argument of sysfs_bin_attr_simple

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Message-ID: <Z3-DcbY60SxoM0dN@infradead.org>
Date: Thu, 9 Jan 2025 00:06:09 -0800
From: Christoph Hellwig <hch@...radead.org>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Alexei Starovoitov <alexei.starovoitov@...il.com>,
	Thomas Weißschuh <linux@...ssschuh.net>,
	Michael Ellerman <mpe@...erman.id.au>,
	Nicholas Piggin <npiggin@...il.com>,
	Christophe Leroy <christophe.leroy@...roup.eu>,
	Naveen N Rao <naveen@...nel.org>,
	Madhavan Srinivasan <maddy@...ux.ibm.com>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	Luis Chamberlain <mcgrof@...nel.org>,
	Petr Pavlu <petr.pavlu@...e.com>,
	Sami Tolvanen <samitolvanen@...gle.com>,
	Daniel Gomez <da.gomez@...sung.com>,
	Alexei Starovoitov <ast@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Andrii Nakryiko <andrii@...nel.org>,
	Martin KaFai Lau <martin.lau@...ux.dev>,
	Eduard Zingerman <eddyz87@...il.com>, Song Liu <song@...nel.org>,
	Yonghong Song <yonghong.song@...ux.dev>,
	John Fastabend <john.fastabend@...il.com>,
	KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...ichev.me>,
	Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
	ppc-dev <linuxppc-dev@...ts.ozlabs.org>,
	LKML <linux-kernel@...r.kernel.org>, linux-modules@...r.kernel.org,
	bpf <bpf@...r.kernel.org>
Subject: Re: [PATCH v2 0/3] sysfs: constify bin_attribute argument of
 sysfs_bin_attr_simple_read()

On Thu, Jan 09, 2025 at 08:56:37AM +0100, Greg Kroah-Hartman wrote:
> The "pointless" penalty will go away once we convert all instances, and
> really, it's just one pointer check, sysfs files should NOT be a hot
> path for anything real, and one more pointer check should be cached and
> not measurable compared to the real logic behind the binary data coming
> from the hardware/kernel, right?
> 
> sysfs is NOT tuned for speed at all, so adding more checks like this
> should be fine.

Hey, when I duplicated the method to convert sysfs over to a proper
seq_file based approach that avoids buffer overflows you basically
came up with the same line that Alexei had here.  And that is a lot
more useful than constification. Not that I mind the latter, but it
would be better if it could be done without leaving both variants
in for long.