Before verify some complicated memory functionalities such as swap memory
and THP, we need add some helper functions to configure and retrieve cgroups
(specifically, memcg).

These helper functions consist:
  Create and destroy individual cgroup for test cases
  attach and dettach the test process to specified cgroup
  Read swap size and thp size from testing cgroup

Signed-off-by: Yongting Lin <linyongting@bytedance.com>
---
 tools/testing/selftests/mshare/util.c | 128 ++++++++++++++++++++++++++
 1 file changed, 128 insertions(+)

diff --git a/tools/testing/selftests/mshare/util.c b/tools/testing/selftests/mshare/util.c
index a3c3896bd507..f1db4eb3cd8f 100644
--- a/tools/testing/selftests/mshare/util.c
+++ b/tools/testing/selftests/mshare/util.c
@@ -124,3 +124,131 @@ int mshare_ioctl_munmap(int fd, size_t size)
 
 	return ioctl(fd, MSHAREFS_UNMAP, &munmap);
 }
+
+/*
+ * Helper functions for cgroup
+ */
+
+#define CGROUP_BASE "/sys/fs/cgroup/"
+#define CGROUP_TEST "mshare-test-XXXXXX"
+
+bool is_cgroup_v2;
+
+__attribute__((constructor))
+void get_cgroup_version(void)
+{
+	if (access(CGROUP_BASE "cgroup.controllers", F_OK) == 0)
+		is_cgroup_v2 = true;
+}
+
+int create_mshare_test_cgroup(char *cgroup, size_t len)
+{
+	if (is_cgroup_v2)
+		snprintf(cgroup, len, "%s/%s", CGROUP_BASE, CGROUP_TEST);
+	else
+		snprintf(cgroup, len, "%s/memory/%s", CGROUP_BASE, CGROUP_TEST);
+
+	char *path = mkdtemp(cgroup);
+
+	if (!path) {
+		perror("mkdtemp");
+		return -1;
+	}
+
+	return 0;
+}
+
+int remove_cgroup(char *cgroup)
+{
+	return rmdir(cgroup);
+}
+
+int write_data_to_cgroup(char *cgroup, char *file, char *data)
+{
+	char filename[128];
+	int fd;
+	int ret;
+
+	snprintf(filename, sizeof(filename), "%s/%s", cgroup, file);
+	fd = open(filename, O_RDWR);
+
+	if (fd == -1)
+		return -1;
+
+	ret = write(fd, data, strlen(data));
+	close(fd);
+
+	return ret;
+}
+
+int attach_to_cgroup(char *cgroup)
+{
+	char pid_str[32];
+
+	snprintf(pid_str, sizeof(pid_str), "%d", getpid());
+	return write_data_to_cgroup(cgroup, "cgroup.procs", pid_str);
+}
+
+/*
+ * Simplely, just move the pid to root memcg as avoid
+ * complicated consideration.
+ */
+int dettach_from_cgroup(char *cgroup)
+{
+	char pid_str[32];
+	char *root_memcg;
+
+	if (is_cgroup_v2)
+		root_memcg = CGROUP_BASE;
+	else
+		root_memcg = CGROUP_BASE "memory";
+
+	snprintf(pid_str, sizeof(pid_str), "%d", getpid());
+	return write_data_to_cgroup(root_memcg, "cgroup.procs", pid_str);
+}
+
+size_t read_data_from_cgroup(char *cgroup, char *file, char *field)
+{
+	char filename[128];
+	FILE *fp;
+	char line[80];
+	size_t size = -1;
+
+	snprintf(filename, sizeof(filename), "%s/%s", cgroup, file);
+	fp = fopen(filename, "r");
+	if (!fp) {
+		perror("fopen");
+		return -1;
+	}
+
+	while (fgets(line, sizeof(line), fp)) {
+		if (!strncmp(line, field, strlen(field))) {
+			char *value = line + strlen(field) + 1;
+
+			size = atol(value);
+			break;
+		}
+	}
+
+	fclose(fp);
+
+	return size;
+}
+
+size_t read_swap_from_cgroup(char *cgroup)
+{
+	if (is_cgroup_v2)
+		return read_data_from_cgroup(cgroup, "memory.stat", "pswpout");
+	else
+		return read_data_from_cgroup(cgroup, "memory.stat", "swap");
+}
+
+size_t read_huge_from_cgroup(char *cgroup)
+{
+	if (is_cgroup_v2)
+		return read_data_from_cgroup(cgroup, "memory.stat", "file_thp")
+		     + read_data_from_cgroup(cgroup, "memory.stat", "anon_thp")
+		     + read_data_from_cgroup(cgroup, "memory.stat", "shmem_thp");
+	else
+		return read_data_from_cgroup(cgroup, "memory.stat", "rss_huge");
+}
-- 
2.20.1