pkg: new package cgroups

provide a package for managing cgroups.  This is not supposed to be a
complete implementation with all the features supported by cgroups,
but it is a minimal implementation designed around what libpod needs
and it is currently using.

For example, it is currently possible to Apply only the pids limit,
as it is used by libpod for stopping containers, any other Apply will
just fail.

The main goal here is to have a minimal library where we have full
control, so we can start playing with cgroup v2.

When the need arises, we can add more features.

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

1 files changed, 62 insertions, 0 deletions

diff --git a/pkg/cgroups/pids.go b/pkg/cgroups/pids.go
new file mode 100644
index 000000000..f37ac7611
--- /dev/null
+++ b/pkg/cgroups/pids.go
@@ -0,0 +1,62 @@
+package cgroups
+
+import (
+	"fmt"
+	"io/ioutil"
+	"os"
+	"path/filepath"
+
+	spec "github.com/opencontainers/runtime-spec/specs-go"
+)
+
+type pidHandler struct {
+}
+
+func getPidsHandler() *pidHandler {
+	return &pidHandler{}
+}
+
+// Apply set the specified constraints
+func (c *pidHandler) Apply(ctr *CgroupControl, res *spec.LinuxResources) error {
+	if res.Pids == nil {
+		return nil
+	}
+	if ctr.cgroup2 {
+		return fmt.Errorf("function not implemented yet")
+	}
+
+	p := filepath.Join(ctr.getCgroupv1Path(Pids), "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 ctr.createCgroupDirectory(Pids)
+}
+
+// Destroy the cgroup
+func (c *pidHandler) Destroy(ctr *CgroupControl) error {
+	return os.Remove(ctr.getCgroupv1Path(Pids))
+}
+
+// Stat fills a metrics structure with usage stats for the controller
+func (c *pidHandler) Stat(ctr *CgroupControl, m *Metrics) error {
+	var PIDRoot string
+
+	if ctr.cgroup2 {
+		return fmt.Errorf("function not implemented yet")
+	}
+
+	PIDRoot := ctr.getCgroupv1Path(Pids)
+
+	current, err := readFileAsUint64(filepath.Join(PIDRoot, "pids.current"))
+	if err != nil {
+		return err
+	}
+
+	m.Pids = PidsMetrics{Current: current}
+	return nil
+}