package libcontainer
import (
"errors"
"fmt"
"os"
"path/filepath"
"golang.org/x/sys/unix"
)
type PressureLevel uint
const (
LowPressure PressureLevel = iota
MediumPressure
CriticalPressure
)
func registerMemoryEvent(cgDir string, evName string, arg string) (<-chan struct{}, error) {
evFile, err := os.Open(filepath.Join(cgDir, evName))
if err != nil {
return nil, err
}
fd, err := unix.Eventfd(0, unix.EFD_CLOEXEC)
if err != nil {
evFile.Close()
return nil, err
}
eventfd := os.NewFile(uintptr(fd), "eventfd")
eventControlPath := filepath.Join(cgDir, "cgroup.event_control")
data := fmt.Sprintf("%d %d %s", eventfd.Fd(), evFile.Fd(), arg)
if err := os.WriteFile(eventControlPath, []byte(data), 0o700); err != nil {
eventfd.Close()
evFile.Close()
return nil, err
}
ch := make(chan struct{})
go func() {
defer func() {
eventfd.Close()
evFile.Close()
close(ch)
}()
buf := make([]byte, 8)
for {
if _, err := eventfd.Read(buf); err != nil {
return
}
// When a cgroup is destroyed, an event is sent to eventfd.
// So if the control path is gone, return instead of notifying.
if _, err := os.Lstat(eventControlPath); os.IsNotExist(err) {
return
}
ch <- struct{}{}
}
}()
return ch, nil
}
// notifyOnOOM returns channel on which you can expect event about OOM,
// if process died without OOM this channel will be closed.
func notifyOnOOM(dir string) (<-chan struct{}, error) {
if dir == "" {
return nil, errors.New("memory controller missing")
}
return registerMemoryEvent(dir, "memory.oom_control", "")
}
func notifyMemoryPressure(dir string, level PressureLevel) (<-chan struct{}, error) {
if dir == "" {
return nil, errors.New("memory controller missing")
}
if level > CriticalPressure {
return nil, fmt.Errorf("invalid pressure level %d", level)
}
levelStr := []string{"low", "medium", "critical"}[level]
return registerMemoryEvent(dir, "memory.pressure_level", levelStr)
}