Re: [PATCH v7 4/8] perf tool: synthesize namespace events for current processes

[Hari Bathini <hbathini@linux.vnet.ibm.com>]

On Thursday 02 March 2017 02:35 AM, Arnaldo Carvalho de Melo wrote:
> Em Tue, Feb 21, 2017 at 07:31:44PM +0530, Hari Bathini escreveu:
>> Synthesize PERF_RECORD_NAMESPACES events for processes that were
>> running prior to invocation of perf record, the data for which is
>> taken from /proc/$PID/ns. These changes make way for analyzing
>> events with regard to namespaces.
>>
>> Signed-off-by: Hari Bathini <hbathini@linux.vnet.ibm.com>
>> ---
>>   tools/perf/builtin-record.c |   27 +++++++++--
>>   tools/perf/util/event.c     |  107 +++++++++++++++++++++++++++++++++++++++++--
>>   tools/perf/util/event.h     |    6 ++
>>   3 files changed, 130 insertions(+), 10 deletions(-)
>>
>> diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
>> index a8b9a78..f4bf6a6 100644
>> --- a/tools/perf/builtin-record.c
>> +++ b/tools/perf/builtin-record.c
>> @@ -986,6 +986,7 @@ static int __cmd_record(struct record *rec, int argc, const char **argv)
>>   	 */
>>   	if (forks) {
>>   		union perf_event *event;
>> +		pid_t tgid;
>>   
>>   		event = malloc(sizeof(event->comm) + machine->id_hdr_size);
>>   		if (event == NULL) {
>> @@ -999,10 +1000,28 @@ static int __cmd_record(struct record *rec, int argc, const char **argv)
>>   		 * cannot see a correct process name for those events.
>>   		 * Synthesize COMM event to prevent it.
>>   		 */
>> -		perf_event__synthesize_comm(tool, event,
>> -					    rec->evlist->workload.pid,
>> -					    process_synthesized_event,
>> -					    machine);
>> +		tgid = perf_event__synthesize_comm(tool, event,
>> +						   rec->evlist->workload.pid,
>> +						   process_synthesized_event,
>> +						   machine);
>> +		free(event);
>> +
>> +		if (tgid == -1)
>> +			goto out_child;
>> +
>> +		event = malloc(sizeof(event->namespaces) + machine->id_hdr_size);
>> +		if (event == NULL) {
>> +			err = -ENOMEM;
>> +			goto out_child;
>> +		}
>> +
>> +		/*
>> +		 * Synthesize NAMESPACES event for the command specified.
>> +		 */
>> +		perf_event__synthesize_namespaces(tool, event,
>> +						  rec->evlist->workload.pid,
>> +						  tgid, process_synthesized_event,
>> +						  machine);
>>   		free(event);
>>   
>>   		perf_evlist__start_workload(rec->evlist);
>> diff --git a/tools/perf/util/event.c b/tools/perf/util/event.c
>> index f118eac..c8c112a 100644
>> --- a/tools/perf/util/event.c
>> +++ b/tools/perf/util/event.c
>> @@ -50,6 +50,16 @@ static const char *perf_event__names[] = {
>>   	[PERF_RECORD_TIME_CONV]			= "TIME_CONV",
>>   };
>>   
>> +static const char *perf_ns__names[] = {
>> +	[NET_NS_INDEX]		= "net",
>> +	[UTS_NS_INDEX]		= "uts",
>> +	[IPC_NS_INDEX]		= "ipc",
>> +	[PID_NS_INDEX]		= "pid",
>> +	[USER_NS_INDEX]		= "user",
>> +	[MNT_NS_INDEX]		= "mnt",
>> +	[CGROUP_NS_INDEX]	= "cgroup",
>> +};
>> +
>>   const char *perf_event__name(unsigned int id)
>>   {
>>   	if (id >= ARRAY_SIZE(perf_event__names))
>> @@ -59,6 +69,13 @@ const char *perf_event__name(unsigned int id)
>>   	return perf_event__names[id];
>>   }
>>   
>> +static const char *perf_ns__name(unsigned int id)
>> +{
>> +	if (id >= ARRAY_SIZE(perf_ns__names))
>> +		return "UNKNOWN";
>> +	return perf_ns__names[id];
>> +}
>> +
>>   static int perf_tool__process_synth_event(struct perf_tool *tool,
>>   					  union perf_event *event,
>>   					  struct machine *machine,
>> @@ -204,6 +221,56 @@ pid_t perf_event__synthesize_comm(struct perf_tool *tool,
>>   	return tgid;
>>   }
>>   
>> +static void perf_event__get_ns_link_info(pid_t pid, const char *ns,
>> +					 struct perf_ns_link_info *ns_link_info)
>> +{
>> +	struct stat64 st;
>> +	char proc_ns[128];
>> +
>> +	sprintf(proc_ns, "/proc/%u/ns/%s", pid, ns);
>> +	if (stat64(proc_ns, &st) == 0) {
>> +		ns_link_info->dev = st.st_dev;
>> +		ns_link_info->ino = st.st_ino;
>> +	}
>> +}
>> +
>> +int perf_event__synthesize_namespaces(struct perf_tool *tool,
>> +				      union perf_event *event,
>> +				      pid_t pid, pid_t tgid,
>> +				      perf_event__handler_t process,
>> +				      struct machine *machine)
>> +{
>> +	u32 idx;
>> +	struct perf_ns_link_info *ns_link_info;
>> +
>> +	if (!tool->namespace_events)
>> +		return 0;
>> +
>> +	memset(&event->namespaces, 0,
>> +	       sizeof(event->namespaces) + machine->id_hdr_size);
>> +
>> +	event->namespaces.pid = tgid;
>> +	event->namespaces.tid = pid;
>> +
>> +	event->namespaces.nr_namespaces = NR_NAMESPACES;
> Huh? Don't you have to first figure out how many namespaces a process is
> in to then set this field?
>

NR_NAMESPACES is the total number of namespaces. For synthesized namespace
events, data is obtained from /proc/<pid>/ns/ dir. Looking at this dir, it
is difficult to arrive at the total number of namespaces in kernel, as
some namespaces can be compiled in/out of the kernel. NR_NAMESPACES is
used instead. Its value is most likely the same for kernel and perf tool
unless a new namespace is introduced - the warning in previous patch is
intended to alert the user about such scenario.

Thanks
Hari