perf namespaces: Introduce nsinfo__set_in_pidns()

When we're processing a perf.data file we will, for every thread in that
file do a machine__findnew_thread(machine, pid, tid) that when that pid
is seen for the first time will create a 'struct thread' representing
it.

That in turn will call nsinfo__new() -> nsinfo__init() and there it will
assume we're running live, which is wrong and will need to be addressed
in a followup patch.

The nsinfo__new() assumes that if we can't access that thread it has
already finished and will ignore the -1 return from nsinfo__init(), just
taking notes to avoid trying to enter in that namespace, since it isn't
there anymore, a race.

When doing this from 'perf inject', tho, we can fill in parts of that
nsinfo from what we get from the PERF_RECORD_MMAP2 (pid, tid) and in the
jitdump file name, that has the form of jit-<PID>.dump.

So if the pid in the jitdump file name is not the one in the
PERF_RECORD_MMAP2, we can assume that its the pid of the process
_inside_ the namespace, and that perf was runing outside that namespace.

This will be done in the following patch.

Reported-by: Francesco Nigro <fnigro@redhat.com>
Reported-by: Ilan Green <igreen@redhat.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Clark Williams <williams@redhat.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: James Clark <james.clark@linaro.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Yonatan Goldschmidt <yonatan.goldschmidt@granulate.io>
Link: https://lore.kernel.org/r/20241206204828.507527-4-acme@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/namespaces.c

@@ -271,6 +271,11 @@ pid_t nsinfo__in_pidns(const struct nsinfo  *nsi)
 	return RC_CHK_ACCESS(nsi)->in_pidns;
 }
 
+void nsinfo__set_in_pidns(struct nsinfo *nsi)
+{
+	RC_CHK_ACCESS(nsi)->in_pidns = true;
+}
+
 void nsinfo__mountns_enter(struct nsinfo *nsi,
 				  struct nscookie *nc)
 {