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Subject: Re: [PATCH v4 6/8] sched: Replace strncmp with str_has_prefix
To:     Chuhong Yuan <hslester96@gmail.com>
Cc:     Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        linux-kernel@vger.kernel.org
References: <20190809071051.17387-1-hslester96@gmail.com>
From:   Valentin Schneider <valentin.schneider@arm.com>
Message-ID: <e10b37c6-25fa-e584-b943-07aa32725198@arm.com>
Date:   Fri, 9 Aug 2019 12:31:15 +0100
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On 09/08/2019 08:10, Chuhong Yuan wrote:
> strncmp(str, const, len) is error-prone because len
> is easy to have typo.
> The example is the hard-coded len has counting error
> or sizeof(const) forgets - 1.
> So we prefer using newly introduced str_has_prefix()
> to substitute such strncmp to make code better.
> 
> Signed-off-by: Chuhong Yuan <hslester96@gmail.com>

I tried to have a look at the series as a whole but it's not properly
threaded (or at least doesn't appear as such on lore), which makes it
unnecessarily annoying to review.

Please make sure to use git-send-email, which should properly thread all
patches (IOW make them in-reply-to the cover letter).


Other than that, I stared at it and it seems fine. It's not that helpful
here since I doubt any of these prefixes will change in the near feature,
but hey, why not.

Reviewed-by: Valentin Schneider <valentin.schneider@arm.com>

> ---
> Changes in v4:
>   - Eliminate assignments in if conditions.
> 
>  kernel/sched/debug.c     |  6 ++++--
>  kernel/sched/isolation.c | 11 +++++++----
>  2 files changed, 11 insertions(+), 6 deletions(-)
> 
> diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
> index f7e4579e746c..a03900523e5d 100644
> --- a/kernel/sched/debug.c
> +++ b/kernel/sched/debug.c
> @@ -102,10 +102,12 @@ static int sched_feat_set(char *cmp)
>  {
>  	int i;
>  	int neg = 0;
> +	size_t len;
>  
> -	if (strncmp(cmp, "NO_", 3) == 0) {
> +	len = str_has_prefix(cmp, "NO_");
> +	if (len) {
>  		neg = 1;
> -		cmp += 3;
> +		cmp += len;
>  	}
>  
>  	i = match_string(sched_feat_names, __SCHED_FEAT_NR, cmp);
> diff --git a/kernel/sched/isolation.c b/kernel/sched/isolation.c
> index ccb28085b114..ea2ead4b1906 100644
> --- a/kernel/sched/isolation.c
> +++ b/kernel/sched/isolation.c
> @@ -141,16 +141,19 @@ __setup("nohz_full=", housekeeping_nohz_full_setup);
>  static int __init housekeeping_isolcpus_setup(char *str)
>  {
>  	unsigned int flags = 0;
> +	size_t len;
>  
>  	while (isalpha(*str)) {
> -		if (!strncmp(str, "nohz,", 5)) {
> -			str += 5;
> +		len = str_has_prefix(str, "nohz,");
> +		if (len) {
> +			str += len;
>  			flags |= HK_FLAG_TICK;
>  			continue;
>  		}
>  
> -		if (!strncmp(str, "domain,", 7)) {
> -			str += 7;
> +		len = str_has_prefix(str, "domain,");
> +		if (len) {
> +			str += len;
>  			flags |= HK_FLAG_DOMAIN;
>  			continue;
>  		}
>