From de60340e51d0a72a2efed7bc864c1fe746cc1055 Mon Sep 17 00:00:00 2001
From: b10s <b1os@bk.ru>
Date: Sun, 15 Nov 2020 23:08:25 +0900
Subject: [PATCH] Improve the getCgroupSubsystemsV1() which uses random record
 per subsystem returned by libcontainercgroups.GetCgroupMounts().

Example array from GetCgroupMounts():
```
[
        {
                Mountpoint: "/sys/fs/cgroup/systemd",
                Root: "/",
                Subsystems: []string len: 1, cap: 1, ["systemd"],},
        {
                Mountpoint: "/sys/fs/cgroup/cpu,cpuacct",
                Root: "/",
                Subsystems: []string len: 2, cap: 2, ["cpu","cpuacct"],},
        {
                Mountpoint: "/sys/fs/cgroup/systemd/some/path",
                Root: "/some/path",
                Subsystems: []string len: 1, cap: 1, ["systemd"],},
]
```
becames a map:
```
[
        "memory": "/sys/fs/cgroup/memory/kubepods",
        "systemd": "/sys/fs/cgroup/systemd/some/path",
]
```
which seems to be wrong.

Using shortest path of mountpoint per subsystem would be more reliable.

reference issue: https://github.com/kubernetes/kubernetes/issues/95488
---
 pkg/kubelet/cm/helpers_linux.go | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/pkg/kubelet/cm/helpers_linux.go b/pkg/kubelet/cm/helpers_linux.go
index 9b115ab5380..aa5c37639dc 100644
--- a/pkg/kubelet/cm/helpers_linux.go
+++ b/pkg/kubelet/cm/helpers_linux.go
@@ -202,8 +202,16 @@ func getCgroupSubsystemsV1() (*CgroupSubsystems, error) {
 	}
 	mountPoints := make(map[string]string, len(allCgroups))
 	for _, mount := range allCgroups {
+		// BEFORE kubelet used a random mount point per cgroups subsystem;
+		// NOW    more deterministic: kubelet use mount point with shortest path;
+		// FUTURE is bright with clear expectation determined in doc.
+		// ref. issue: https://github.com/kubernetes/kubernetes/issues/95488
+
 		for _, subsystem := range mount.Subsystems {
-			mountPoints[subsystem] = mount.Mountpoint
+			previous := mountPoints[subsystem]
+			if previous == "" || len(mount.Mountpoint) < len(previous) {
+				mountPoints[subsystem] = mount.Mountpoint
+			}
 		}
 	}
 	return &CgroupSubsystems{