perf namespaces: Add 'in_pidns' to nsinfo struct

Provides an accurate mean to determine if the owner thread is in a
different PID namespace.

Signed-off-by: Yonatan Goldschmidt <[e-mail]>
Acked-by: Jiri Olsa <[e-mail]>
Acked-by: Namhyung Kim <[e-mail]>
Cc: Alexander Shishkin <[e-mail]>
Cc: Ingo Molnar <[e-mail]>
Cc: Mark Rutland <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Stephane Eranian <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/util/namespaces.c

···
 	char spath[PATH_MAX];
 	char *newns = NULL;
 	char *statln = NULL;
+	char *nspid;
 	struct stat old_stat;
 	struct stat new_stat;
 	FILE *f = NULL;
···
 		}
 
 		if (strstr(statln, "NStgid:") != NULL) {
-			nsi->nstgid = (pid_t)strtol(strrchr(statln, '\t'),
-						     NULL, 10);
+			nspid = strrchr(statln, '\t');
+			nsi->nstgid = (pid_t)strtol(nspid, NULL, 10);
+			/* If innermost tgid is not the first, process is in a different
+			 * PID namespace.
+			 */
+			nsi->in_pidns = (statln + sizeof("NStgid:") - 1) != nspid;
 			break;
 		}
 	}
···
 		nsi->tgid = pid;
 		nsi->nstgid = pid;
 		nsi->need_setns = false;
+		nsi->in_pidns = false;
 		/* Init may fail if the process exits while we're trying to look
 		 * at its proc information.  In that case, save the pid but
 		 * don't try to enter the namespace.
···
 		nnsi->tgid = nsi->tgid;
 		nnsi->nstgid = nsi->nstgid;
 		nnsi->need_setns = nsi->need_setns;
+		nnsi->in_pidns = nsi->in_pidns;
 		if (nsi->mntns_path) {
 			nnsi->mntns_path = strdup(nsi->mntns_path);
 			if (!nnsi->mntns_path) {

tools/perf/util/namespaces.h

···
 	pid_t			tgid;
 	pid_t			nstgid;
 	bool			need_setns;
+	bool			in_pidns;
 	char			*mntns_path;
 	refcount_t		refcnt;
 };