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

Thomas-Mich Richter
2018-06-14T14:10:46Z

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@linux.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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