[PATCH V2 1/2] tools/perf: Add utility function to read /proc/cpuinfo for any field

[Athira Rajeev]

> On 05-May-2022, at 10:54 PM, Arnaldo Carvalho de Melo <acme at kernel.org> wrote:
> 
> Em Thu, May 05, 2022 at 03:09:59PM +0530, Athira Rajeev escreveu:
>> /proc/cpuinfo provides information about type of processor, number
>> of CPU's etc. Reading /proc/cpuinfo file outputs useful information
>> by field name like cpu, platform, model (depending on architecture)
>> and its value separated by colon.
>> 
>> Add new utility function "cpuinfo_field" in "util/header.c" which
>> accepts field name as input string to search in /proc/cpuinfo content.
>> This returns the first matching value as resulting string. Example,
>> calling the function "cpuinfo_field(platform)" in powerpc returns
>> the platform value. This can be used to fetch processor information
>> from "cpuinfo" by other utilities/testcases.
>> 
>> Signed-off-by: Athira Rajeev <atrajeev at linux.vnet.ibm.com>
>> ---
>> tools/perf/util/header.c | 53 ++++++++++++++++++++++++++++++++++++++++
>> tools/perf/util/header.h |  1 +
>> 2 files changed, 54 insertions(+)
>> 
>> diff --git a/tools/perf/util/header.c b/tools/perf/util/header.c
>> index a27132e5a5ef..f08857f96606 100644
>> --- a/tools/perf/util/header.c
>> +++ b/tools/perf/util/header.c
>> @@ -983,6 +983,59 @@ static int write_dir_format(struct feat_fd *ff,
>> 	return do_write(ff, &data->dir.version, sizeof(data->dir.version));
>> }
>> 
>> +/*
>> + * Return entry from /proc/cpuinfo
>> + * indicated by "search" parameter.
>> + */
>> +char *cpuinfo_field(const char *search)
>> +{
>> +	FILE *file;
>> +	char *buf = NULL;
>> +	char *copy_buf = NULL, *p;
>> +	size_t len = 0;
>> +
>> +	if (!search)
>> +		return NULL;
>> +
>> +	file = fopen("/proc/cpuinfo", "r");
>> +	if (!file)
>> +		return NULL;
>> +
>> +	while (getline(&buf, &len, file) > 0) {
>> +		if (!strncmp(buf, search, strlen(search)))
> 
> Can you save the search string lenght in a variable and use it instead
> of calling strlen() for the same buffer for each line in /proc/cpuinfo?


Hi Arnaldo, Michael

Thanks for review comments. Based on suggestion from Michael, I am reworking on patch 2 to SKIP the test
if physical_id is set to -1 irrespective of value from cpuinfo.

In this patch, I had written "cpuinfo_field " function as generic function for retrieving any entry from /proc/cpuinfo.
But it won't be used in patch 2 now. Do you think this function is useful to keep ? Otherwise, I will drop patch 1

Thanks
Athira Rajeev

> 
>> +			break;
>> +	}
>> +
>> +	if (feof(file))
>> +		goto done;
>> +
>> +	/*
>> +	 * Trim the new line and separate
>> +	 * value for search field from ":"
>> +	 * in cpuinfo line output.
>> +	 * Example output line:
>> +	 * platform : <value>
>> +	 */
>> +	copy_buf = buf;
>> +	p = strchr(copy_buf, ':');
> 
> So you assume that this will always be there, right? Shouldn't we not
> assume that and check if p is NULL and bail out instead?
> 
>> +
>> +	/* Go to string after ":" */
>> +	copy_buf = p + 1;
>> +	p = strchr(copy_buf, '\n');
> 
> Ditto.
> 
>> +	if (p)
>> +		*p = '\0';
>> +
>> +	/* Copy the filtered string after removing space to buf */
>> +	strcpy(buf, strim(copy_buf));
>> +
>> +	fclose(file);
>> +	return buf;
>> +
>> +done:
> 
> Please rename this goto label to "not_found", "done" isn't intention
> revealing.
> 
>> +	free(buf);
>> +	fclose(file);
>> +	return NULL;
>> +}
>> /*
>>  * Check whether a CPU is online
>>  *
>> diff --git a/tools/perf/util/header.h b/tools/perf/util/header.h
>> index 0eb4bc29a5a4..b0f754364bd4 100644
>> --- a/tools/perf/util/header.h
>> +++ b/tools/perf/util/header.h
>> @@ -166,4 +166,5 @@ int get_cpuid(char *buffer, size_t sz);
>> 
>> char *get_cpuid_str(struct perf_pmu *pmu __maybe_unused);
>> int strcmp_cpuid_str(const char *s1, const char *s2);
>> +char *cpuinfo_field(const char *search);
>> #endif /* __PERF_HEADER_H */
>> -- 
>> 2.35.1
> 
> -- 
> 
> - Arnaldo