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Date: Mon, 13 Jan 2025 17:46:43 -0600
From: Rob Herring <robh@kernel.org>
To: Zijun Hu <zijun_hu@icloud.com>
Cc: Saravana Kannan <saravanak@google.com>,
	Maxime Ripard <mripard@kernel.org>,
	Robin Murphy <robin.murphy@arm.com>,
	Grant Likely <grant.likely@secretlab.ca>,
	Marc Zyngier <maz@kernel.org>,
	Andreas Herrmann <andreas.herrmann@calxeda.com>,
	Marek Szyprowski <m.szyprowski@samsung.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Mike Rapoport <rppt@kernel.org>,
	Oreoluwa Babatunde <quic_obabatun@quicinc.com>,
	devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
	Zijun Hu <quic_zijuhu@quicinc.com>
Subject: Re: [PATCH v4 14/14] of: Improve __of_add_property_sysfs()
 readability
Message-ID: <20250113234643.GA3631169-robh@kernel.org>
References: <20250109-of_core_fix-v4-0-db8a72415b8c@quicinc.com>
 <20250109-of_core_fix-v4-14-db8a72415b8c@quicinc.com>
 <20250110204154.GA3529721-robh@kernel.org>
 <954725b5-5d53-4bd0-9a06-61ac1aa35dfe@icloud.com>
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In-Reply-To: <954725b5-5d53-4bd0-9a06-61ac1aa35dfe@icloud.com>

On Mon, Jan 13, 2025 at 11:00:12PM +0800, Zijun Hu wrote:
> On 2025/1/11 04:41, Rob Herring wrote:
> >> From: Zijun Hu <quic_zijuhu@quicinc.com>
> >>
> >> __of_add_property_sysfs() hard codes string "security-" length as 9, but
> >> that is not obvious for readers.
> >>
> >> Improve its readability by using strlen().
> > Does the compiler optimize the strlen call away? Maybe, maybe not. If 
> > not, that's N calls to strlen() where N is the number of properties in 
> > your DT. That's in the 1000s easily.
> > 
> > Do you really want to go test enough compiler versions we support to 
> > feel confident this is optimized away. I don't.
> 
> i understand your concern about performance.
> 
> what about below solution ?

See 72921427d46b ("string.h: Add str_has_prefix() helper function"). 

Though we already had strstarts(), but that lacks __always_inline which 
seems is important for eliminating the strlen(). Also, since that 
commit, clang has become more common and need to make sure the same 
optimization happens on it.

> 
>  int __of_add_property_sysfs(struct device_node *np, struct property *pp)
>  {
> +#define SECURITY_PREFIX "security-"
>         int rc;
> 
>         /* Important: Don't leak passwords */
> -       bool secure = strncmp(pp->name, "security-", 9) == 0;
> +       bool secure = strncmp(pp->name, SECURITY_PREFIX,
> sizeof(SECURITY_PREFIX) - 1) == 0;
> 
>         if (!IS_ENABLED(CONFIG_SYSFS))
>                 return 0;
> 
> 
>