runc/libcontainer/cgroups/fs/cpuset.go

// +build linux

package fs

import (
	"os"
	"path/filepath"

	"github.com/opencontainers/runc/libcontainer/cgroups"
	"github.com/opencontainers/runc/libcontainer/cgroups/fscommon"
	"github.com/opencontainers/runc/libcontainer/configs"
	"golang.org/x/sys/unix"
)

type CpusetGroup struct {
}

func (s *CpusetGroup) Name() string {
	return "cpuset"
}

func (s *CpusetGroup) Apply(path string, d *cgroupData) error {
	return s.ApplyDir(path, d.config, d.pid)
}

func (s *CpusetGroup) Set(path string, cgroup *configs.Cgroup) error {
	if cgroup.Resources.CpusetCpus != "" {
		if err := fscommon.WriteFile(path, "cpuset.cpus", cgroup.Resources.CpusetCpus); err != nil {
			return err
		}
	}
	if cgroup.Resources.CpusetMems != "" {
		if err := fscommon.WriteFile(path, "cpuset.mems", cgroup.Resources.CpusetMems); err != nil {
			return err
		}
	}
	return nil
}

func (s *CpusetGroup) GetStats(path string, stats *cgroups.Stats) error {
	return nil
}

func (s *CpusetGroup) ApplyDir(dir string, cgroup *configs.Cgroup, pid int) error {
	// This might happen if we have no cpuset cgroup mounted.
	// Just do nothing and don't fail.
	if dir == "" {
		return nil
	}
	// 'ensureParent' start with parent because we don't want to
	// explicitly inherit from parent, it could conflict with
	// 'cpuset.cpu_exclusive'.
	if err := cpusetEnsureParent(filepath.Dir(dir)); err != nil {
		return err
	}
	if err := os.MkdirAll(dir, 0755); err != nil {
		return err
	}
	// We didn't inherit cpuset configs from parent, but we have
	// to ensure cpuset configs are set before moving task into the
	// cgroup.
	// The logic is, if user specified cpuset configs, use these
	// specified configs, otherwise, inherit from parent. This makes
	// cpuset configs work correctly with 'cpuset.cpu_exclusive', and
	// keep backward compatibility.
	if err := s.ensureCpusAndMems(dir, cgroup); err != nil {
		return err
	}

	// because we are not using d.join we need to place the pid into the procs file
	// unlike the other subsystems
	return cgroups.WriteCgroupProc(dir, pid)
}

func getCpusetSubsystemSettings(parent string) (cpus, mems string, err error) {
	if cpus, err = fscommon.ReadFile(parent, "cpuset.cpus"); err != nil {
		return
	}
	if mems, err = fscommon.ReadFile(parent, "cpuset.mems"); err != nil {
		return
	}
	return cpus, mems, nil
}

// cpusetEnsureParent makes sure that the parent directories of current
// are created and populated with the proper cpus and mems files copied
// from their respective parent. It does that recursively, starting from
// the top of the cpuset hierarchy (i.e. cpuset cgroup mount point).
func cpusetEnsureParent(current string) error {
	var st unix.Statfs_t

	parent := filepath.Dir(current)
	err := unix.Statfs(parent, &st)
	if err == nil && st.Type != unix.CGROUP_SUPER_MAGIC {
		return nil
	}
	// Treat non-existing directory as cgroupfs as it will be created,
	// and the root cpuset directory obviously exists.
	if err != nil && err != unix.ENOENT {
		return &os.PathError{Op: "statfs", Path: parent, Err: err}
	}

	if err := cpusetEnsureParent(parent); err != nil {
		return err
	}
	if err := os.MkdirAll(current, 0755); err != nil {
		return err
	}
	return cpusetCopyIfNeeded(current, parent)
}

// cpusetCopyIfNeeded copies the cpuset.cpus and cpuset.mems from the parent
// directory to the current directory if the file's contents are 0
func cpusetCopyIfNeeded(current, parent string) error {
	currentCpus, currentMems, err := getCpusetSubsystemSettings(current)
	if err != nil {
		return err
	}
	parentCpus, parentMems, err := getCpusetSubsystemSettings(parent)
	if err != nil {
		return err
	}

	if isEmptyCpuset(currentCpus) {
		if err := fscommon.WriteFile(current, "cpuset.cpus", string(parentCpus)); err != nil {
			return err
		}
	}
	if isEmptyCpuset(currentMems) {
		if err := fscommon.WriteFile(current, "cpuset.mems", string(parentMems)); err != nil {
			return err
		}
	}
	return nil
}

func isEmptyCpuset(str string) bool {
	return str == "" || str == "\n"
}

func (s *CpusetGroup) ensureCpusAndMems(path string, cgroup *configs.Cgroup) error {
	if err := s.Set(path, cgroup); err != nil {
		return err
	}
	return cpusetCopyIfNeeded(path, filepath.Dir(path))
}