kselftest/cgroup: Add cpuset v2 partition root state test

Add a test script test_cpuset_prs.sh with a helper program wait_inotify
for exercising the cpuset v2 partition root state code.
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

tools/testing/selftests/cgroup/.gitignore

@@ -5,3 +5,4 @@ test_freezer
 test_kmem
 test_kill
 test_cpu
+wait_inotify

tools/testing/selftests/cgroup/Makefile

 # SPDX-License-Identifier: GPL-2.0
 CFLAGS += -Wall -pthread
 
-all:
+all: ${HELPER_PROGS}
 
 TEST_FILES     := with_stress.sh
-TEST_PROGS     := test_stress.sh
+TEST_PROGS     := test_stress.sh test_cpuset_prs.sh
+TEST_GEN_FILES := wait_inotify
 TEST_GEN_PROGS = test_memcontrol
 TEST_GEN_PROGS += test_kmem
 TEST_GEN_PROGS += test_core

tools/testing/selftests/cgroup/wait_inotify.c

+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Wait until an inotify event on the given cgroup file.
+ */
+#include <linux/limits.h>
+#include <sys/inotify.h>
+#include <sys/mman.h>
+#include <sys/ptrace.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <poll.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+static const char usage[] = "Usage: %s [-v] <cgroup_file>\n";
+static char *file;
+static int verbose;
+
+static inline void fail_message(char *msg)
+{
+	fprintf(stderr, msg, file);
+	exit(1);
+}
+
+int main(int argc, char *argv[])
+{
+	char *cmd = argv[0];
+	int c, fd;
+	struct pollfd fds = { .events = POLLIN, };
+
+	while ((c = getopt(argc, argv, "v")) != -1) {
+		switch (c) {
+		case 'v':
+			verbose++;
+			break;
+		}
+		argv++, argc--;
+	}
+
+	if (argc != 2) {
+		fprintf(stderr, usage, cmd);
+		return -1;
+	}
+	file = argv[1];
+	fd = open(file, O_RDONLY);
+	if (fd < 0)
+		fail_message("Cgroup file %s not found!\n");
+	close(fd);
+
+	fd = inotify_init();
+	if (fd < 0)
+		fail_message("inotify_init() fails on %s!\n");
+	if (inotify_add_watch(fd, file, IN_MODIFY) < 0)
+		fail_message("inotify_add_watch() fails on %s!\n");
+	fds.fd = fd;
+
+	/*
+	 * poll waiting loop
+	 */
+	for (;;) {
+		int ret = poll(&fds, 1, 10000);
+
+		if (ret < 0) {
+			if (errno == EINTR)
+				continue;
+			perror("poll");
+			exit(1);
+		}
+		if ((ret > 0) && (fds.revents & POLLIN))
+			break;
+	}
+	if (verbose) {
+		struct inotify_event events[10];
+		long len;
+
+		usleep(1000);
+		len = read(fd, events, sizeof(events));
+		printf("Number of events read = %ld\n",
+			len/sizeof(struct inotify_event));
+	}
+	close(fd);
+	return 0;
+}