Bugfix: can't write to cpuset cgroup

WeiZhang555 · WeiZhang555 · commit 13aaafdc37e7 · 2018-09-14T11:18:51.000+08:00
Using linux resource in spec:

```
"resources": {
    "cpu": {
        "period": 100000,
        "quota": 40000
    },
...
}
```

In this case, `resources.CPU` != nil but `resources.CPU.Cpus` and `resources.CPU.Mems`
are empty strings, `cgroups` lib will write "" to cpuset.cpus and cpuset.mems in
Cpuset group, then no process can be written in this cgroup any more.

In this case, empty value means copying from parent but doesn't mean no CPU can
be used in this cgroup.

Signed-off-by: Wei Zhang &lt;zhangwei555@huawei.com&gt;
diff --git a/cpuset.go b/cpuset.go
@@ -57,21 +57,21 @@ func (c *cpusetController) Create(path string, resources *specs.LinuxResources)
 	if resources.CPU != nil {
 		for _, t := range []struct {
 			name  string
-			value *string
+			value string
 		}{
 			{
 				name:  "cpus",
-				value: &resources.CPU.Cpus,
+				value: resources.CPU.Cpus,
 			},
 			{
 				name:  "mems",
-				value: &resources.CPU.Mems,
+				value: resources.CPU.Mems,
 			},
 		} {
-			if t.value != nil {
+			if t.value != "" {
 				if err := ioutil.WriteFile(
 					filepath.Join(c.Path(path), fmt.Sprintf("cpuset.%s", t.name)),
-					[]byte(*t.value),
+					[]byte(t.value),
 					defaultFilePerm,
 				); err != nil {
 					return err
