linux-kernel - Re: [PATCH 1/3] perf alias: Remove trailing newline when reading sysfs files

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Date:   Thu, 14 Jun 2018 16:10:31 +0200
From:   Thomas-Mich Richter <tmricht@...ux.ibm.com>
To:     Paul Clarke <pc@...ibm.com>, linux-kernel@...r.kernel.org,
        linux-perf-users@...r.kernel.org, acme@...nel.org, jolsa@...hat.com
Cc:     brueckner@...ux.vnet.ibm.com, schwidefsky@...ibm.com,
        heiko.carstens@...ibm.com
Subject: Re: [PATCH 1/3] perf alias: Remove trailing newline when reading
 sysfs files

On 06/14/2018 03:17 PM, Paul Clarke wrote:
> On 06/14/2018 06:48 AM, Thomas Richter wrote:
>> Remove a trailing newline when reading sysfs file contents
>> such as /sys/devices/cpum_cf/events/TX_NC_TEND.
>> This show when verbose option -v is used.
>>
>> Output before:
>> tx_nc_tend -> 'cpum_cf'/'event=0x008d
>> '/
>>
>> Output after:
>> tx_nc_tend -> 'cpum_cf'/'event=0x8d'/
>>
>> Signed-off-by: Thomas Richter <tmricht@...ux.ibm.com>
>> ---
>>  tools/perf/util/pmu.c | 7 ++++++-
>>  1 file changed, 6 insertions(+), 1 deletion(-)
>>
>> diff --git a/tools/perf/util/pmu.c b/tools/perf/util/pmu.c
>> index 7878934ebb23..26c79a9c4142 100644
>> --- a/tools/perf/util/pmu.c
>> +++ b/tools/perf/util/pmu.c
>> @@ -294,7 +294,7 @@ static int __perf_pmu__new_alias(struct list_head *list, char *dir, char *name,
>>
>>  static int perf_pmu__new_alias(struct list_head *list, char *dir, char *name, FILE *file)
>>  {
>> -	char buf[256];
>> +	char *cp, buf[256];
>>  	int ret;
>>
>>  	ret = fread(buf, 1, sizeof(buf), file);
>> @@ -303,6 +303,11 @@ static int perf_pmu__new_alias(struct list_head *list, char *dir, char *name, FI
>>
>>  	buf[ret] = 0;
>>
>> +	/* Remove trailing newline from sysfs file */
>> +	cp = strrchr(buf, '\n');
>> +	if (cp)
>> +		*cp = '\0';
> 
> A nit, perhaps, but this will search backwards through the entire string if a newline is not found, which is the most common case, I presume.  Would it be more efficient to just look at the last character?  Something like:
> i = strlen(buf);
> if (i > 0 && buf[i-1] == '\n')
>   buf[i-1] = '\0';
> 
>> +
>>  	return __perf_pmu__new_alias(list, dir, name, NULL, buf, NULL, NULL, NULL,
>>  				     NULL, NULL, NULL);
>>  }
>>
> 
> PC
> 

Arnaldo suggested rtrim() which I will use.
I agree that your approach is a bit faster...



-- 
Thomas Richter, Dept 3303, IBM s390 Linux Development, Boeblingen, Germany
--
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