pkg, cgroups: add initial support for cgroup v2

This is an initial implementation of cgroup v2 support for
pkg/cgroups.  It currently works with crun, with this patch:
https://github.com/giuseppe/crun/pull/49).

It adds the pieces for:

- set PID limit to 1
- retrieve stats so that "podman stats" work.

the only missing part is the support for reading per
CPU stats (that is cpuacct.usage_percpu on cgroup v1), so for now it
always returns an empty result.

Signed-off-by: Giuseppe Scrivano <gscrivan@redhat.com>

1 files changed, 10 insertions, 6 deletions

diff --git a/pkg/cgroups/pids.go b/pkg/cgroups/pids.go
index 342b25d85..c90dc1c02 100644
--- a/pkg/cgroups/pids.go
+++ b/pkg/cgroups/pids.go
@@ -21,18 +21,22 @@ func (c *pidHandler) Apply(ctr *CgroupControl, res *spec.LinuxResources) error {
 	if res.Pids == nil {
 		return nil
 	}
+	var PIDRoot string
+
 	if ctr.cgroup2 {
-		return fmt.Errorf("function not implemented yet")
+		PIDRoot = filepath.Join(cgroupRoot, ctr.path)
+	} else {
+		PIDRoot = ctr.getCgroupv1Path(Pids)
 	}
 
-	p := filepath.Join(ctr.getCgroupv1Path(Pids), "pids.max")
+	p := filepath.Join(PIDRoot, "pids.max")
 	return ioutil.WriteFile(p, []byte(fmt.Sprintf("%d\n", res.Pids.Limit)), 0644)
 }
 
 // Create the cgroup
 func (c *pidHandler) Create(ctr *CgroupControl) (bool, error) {
 	if ctr.cgroup2 {
-		return false, fmt.Errorf("function not implemented yet")
+		return false, fmt.Errorf("pid create not implemented for cgroup v2")
 	}
 	return ctr.createCgroupDirectory(Pids)
 }
@@ -47,11 +51,11 @@ func (c *pidHandler) Stat(ctr *CgroupControl, m *Metrics) error {
 	var PIDRoot string
 
 	if ctr.cgroup2 {
-		return fmt.Errorf("function not implemented yet")
+		PIDRoot = filepath.Join(cgroupRoot, ctr.path)
+	} else {
+		PIDRoot = ctr.getCgroupv1Path(Pids)
 	}
 
-	PIDRoot = ctr.getCgroupv1Path(Pids)
-
 	current, err := readFileAsUint64(filepath.Join(PIDRoot, "pids.current"))
 	if err != nil {
 		return err