selftests: cgroup: Add task migration tests

Add two new tests that verify that thread and threadgroup migrations
work as expected.

Signed-off-by: Michal Koutný <mkoutny@suse.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

tools/testing/selftests/cgroup/cgroup_util.c

@@ -158,6 +158,22 @@ long cg_read_key_long(const char *cgroup, const char *control, const char *key)
 	return atol(ptr + strlen(key));
 }
 
+long cg_read_lc(const char *cgroup, const char *control)
+{
+	char buf[PAGE_SIZE];
+	const char delim[] = "\n";
+	char *line;
+	long cnt = 0;
+
+	if (cg_read(cgroup, control, buf, sizeof(buf)))
+		return -1;
+
+	for (line = strtok(buf, delim); line; line = strtok(NULL, delim))
+		cnt++;
+
+	return cnt;
+}
+
 int cg_write(const char *cgroup, const char *control, char *buf)
 {
 	char path[PATH_MAX];
@@ -424,3 +440,13 @@ ssize_t proc_read_text(int pid, bool thread, const char *item, char *buf, size_t
 
 	return read_text(path, buf, size);
 }
+
+int proc_read_strstr(int pid, bool thread, const char *item, const char *needle)
+{
+	char buf[PAGE_SIZE];
+
+	if (proc_read_text(pid, thread, item, buf, sizeof(buf)) < 0)
+		return -1;
+
+	return strstr(buf, needle) ? 0 : -1;
+}