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

[Athira Rajeev]

> On 06-May-2022, at 3:03 PM, Athira Rajeev <atrajeev at linux.vnet.ibm.com> wrote:
> 
> 
> 
>> 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

Hi,

Requesting for suggestions on this change

Thanks
Athira
> 
> 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