Re: [PATCH V3 01/17] perf pmu: Add support for PMU capabilities

["Liang, Kan" <kan.liang@linux.intel.com>]

On 3/18/2020 3:47 PM, Arnaldo Carvalho de Melo wrote:
> Em Fri, Mar 13, 2020 at 11:33:03AM -0700, kan.liang@linux.intel.com escreveu:
>> From: Kan Liang <kan.liang@linux.intel.com>
>>
>> The PMU capabilities information, which is located at
>> /sys/bus/event_source/devices/<dev>/caps, is required by perf tool.
>> For example, the max LBR information is required to stitch LBR call
>> stack.
>>
>> Add perf_pmu__caps_parse() to parse the PMU capabilities information.
>> The information is stored in a list.
>>
>> Add perf_pmu__scan_caps() to scan the capabilities one by one.
>>
>> The following patch will store the capabilities information in perf
>> header.
>>
>> Reviewed-by: Andi Kleen <ak@linux.intel.com>
>> Signed-off-by: Kan Liang <kan.liang@linux.intel.com>
>> ---
>>   tools/perf/util/pmu.c | 98 +++++++++++++++++++++++++++++++++++++++++++
>>   tools/perf/util/pmu.h | 12 ++++++
>>   2 files changed, 110 insertions(+)
>>
>> diff --git a/tools/perf/util/pmu.c b/tools/perf/util/pmu.c
>> index 8b99fd312aae..4cdfbb669567 100644
>> --- a/tools/perf/util/pmu.c
>> +++ b/tools/perf/util/pmu.c
>> @@ -844,6 +844,7 @@ static struct perf_pmu *pmu_lookup(const char *name)
>>   
>>   	INIT_LIST_HEAD(&pmu->format);
>>   	INIT_LIST_HEAD(&pmu->aliases);
>> +	INIT_LIST_HEAD(&pmu->caps);
>>   	list_splice(&format, &pmu->format);
>>   	list_splice(&aliases, &pmu->aliases);
>>   	list_add_tail(&pmu->list, &pmus);
>> @@ -1565,3 +1566,100 @@ int perf_pmu__scan_file(struct perf_pmu *pmu, const char *name, const char *fmt,
>>   	va_end(args);
>>   	return ret;
>>   }
>> +
>> +static int perf_pmu__new_caps(struct list_head *list, char *name, char *value)
>> +{
>> +	struct perf_pmu_caps *caps;
>> +
>> +	caps = zalloc(sizeof(*caps));
>> +	if (!caps)
>> +		return -ENOMEM;
> 
> Since there will be a v4 for other reasons, please combine the
> declaration plus assignment when possible, like above, i.e. make it:
> 

Sure.

> +	struct perf_pmu_caps *caps = zalloc(sizeof(*caps));
> +
> +	if (!caps)
> +		return -ENOMEM;
> 
>> +
>> +	caps->name = strdup(name);
>> +	if (!caps->name)
>> +		goto free_caps;
>> +	caps->value = strndup(value, strlen(value) - 1);
>> +	if (!caps->value)
>> +		goto free_name;
>> +	list_add_tail(&caps->list, list);
>> +	return 0;
>> +
>> +free_name:
>> +	free(caps->name);
> 
> In these cases I think this is preferred:
> 
> 	zfree(&caps->name);

Sure.

> 
>> +free_caps:
>> +	free(caps);
>> +
>> +	return -ENOMEM;
>> +}
>> +
>> +/*
>> + * Reading/parsing the given pmu capabilities, which should be located at:
>> + * /sys/bus/event_source/devices/<dev>/caps as sysfs group attributes.
>> + * Return the number of capabilities
>> + */
>> +int perf_pmu__caps_parse(struct perf_pmu *pmu)
>> +{
>> +	struct stat st;
>> +	char caps_path[PATH_MAX];
>> +	const char *sysfs = sysfs__mountpoint();
>> +	DIR *caps_dir;
>> +	struct dirent *evt_ent;
>> +	int nr_caps = 0;
>> +
>> +	if (!sysfs)
>> +		return -1;
>> +
>> +	snprintf(caps_path, PATH_MAX,
>> +		 "%s" EVENT_SOURCE_DEVICE_PATH "%s/caps", sysfs, pmu->name);
>> +
>> +	if (stat(caps_path, &st) < 0)
>> +		return 0;	/* no error if caps does not exist */
>> +
>> +	caps_dir = opendir(caps_path);
>> +	if (!caps_dir)
>> +		return -EINVAL;
>> +
>> +	while ((evt_ent = readdir(caps_dir)) != NULL) {
>> +		char path[PATH_MAX + NAME_MAX + 1];
>> +		char *name = evt_ent->d_name;
>> +		char value[128];
>> +		FILE *file;
>> +
>> +		if (!strcmp(name, ".") || !strcmp(name, ".."))
>> +			continue;
>> +
>> +		snprintf(path, sizeof(path), "%s/%s", caps_path, name);
>> +
>> +		file = fopen(path, "r");
>> +		if (!file)
>> +			break;
> 
> I haven't looked at what is in such directories that would justify still
> returning whatever was read so far when failing to read one of its
> files, is this sensible? Care to explain a bit why you think so? Looks
> fishy :-\

There is no dependency among the 'capabilities'. If perf fails to read 
one, it should not impact others.
Yes, 'continue' looks better here.


> 
>> +
>> +		if (!fgets(value, sizeof(value), file) ||
>> +		    (perf_pmu__new_caps(&pmu->caps, name, value) < 0)) {
>> +			fclose(file);
>> +			break;
>> +		}
>> +
>> +		nr_caps++;
>> +		fclose(file);
>> +	}
>> +
>> +	closedir(caps_dir);
>> +
>> +	return nr_caps;
>> +}
>> +
>> +struct perf_pmu_caps *perf_pmu__scan_caps(struct perf_pmu *pmu,
>> +					  struct perf_pmu_caps *caps)
>> +{
>> +	if (!pmu)
>> +		return NULL;
>> +
>> +	if (!caps)
>> +		caps = list_prepare_entry(caps, &pmu->caps, list);
>> +
>> +	list_for_each_entry_continue(caps, &pmu->caps, list)
>> +		return caps;
> 
> Why not:
> 
> 	return caps ? list_next_entry(caps) : list_first_entry(&pmu->caps, struct perf_pmu_caps, list);
> 
> Nah, it'll return the head after the last entry, not NULL, argh.
> 
> Anyway, looks like a confusing API :-\
> 
> I'll see how it is used in the following patches...


As suggested in other thread, I will use list_for_each_entry() to 
replace in v4.

Thanks,
Kan

> 
>> +
>> +	return NULL;
>> +}
>> diff --git a/tools/perf/util/pmu.h b/tools/perf/util/pmu.h
>> index 6737e3d5d568..a228e27ae462 100644
>> --- a/tools/perf/util/pmu.h
>> +++ b/tools/perf/util/pmu.h
>> @@ -21,6 +21,12 @@ enum {
>>   
>>   struct perf_event_attr;
>>   
>> +struct perf_pmu_caps {
>> +	char *name;
>> +	char *value;
>> +	struct list_head list;
>> +};
>> +
>>   struct perf_pmu {
>>   	char *name;
>>   	__u32 type;
>> @@ -32,6 +38,7 @@ struct perf_pmu {
>>   	struct perf_cpu_map *cpus;
>>   	struct list_head format;  /* HEAD struct perf_pmu_format -> list */
>>   	struct list_head aliases; /* HEAD struct perf_pmu_alias -> list */
>> +	struct list_head caps;    /* HEAD struct perf_pmu_caps -> list */
>>   	struct list_head list;    /* ELEM */
>>   };
>>   
>> @@ -102,4 +109,9 @@ struct pmu_events_map *perf_pmu__find_map(struct perf_pmu *pmu);
>>   
>>   int perf_pmu__convert_scale(const char *scale, char **end, double *sval);
>>   
>> +int perf_pmu__caps_parse(struct perf_pmu *pmu);
>> +
>> +struct perf_pmu_caps *perf_pmu__scan_caps(struct perf_pmu *pmu,
>> +					  struct perf_pmu_caps *caps);
>> +
>>   #endif /* __PMU_H */
>> -- 
>> 2.17.1
>>
>