Copyright © 2022 Oleg Pykhalov <go.wigust@gmail.com>

Create a PID file after containerd is ready to serve requests.

Fixes <https://issues.guix.gnu.org/38432>.

--- a/cmd/containerd/command/notify_linux.go	1970-01-01 03:00:01.000000000 +0300
+++ b/cmd/containerd/command/notify_linux.go	2022-07-02 04:42:35.553753495 +0300
@@ -22,15 +22,22 @@
 	sd "github.com/coreos/go-systemd/v22/daemon"
 
 	"github.com/containerd/containerd/log"
+
+	"os"
+	"strconv"
 )
 
 // notifyReady notifies systemd that the daemon is ready to serve requests
 func notifyReady(ctx context.Context) error {
+	pidFile, _ := os.Create("/run/containerd/containerd.pid")
+	defer pidFile.Close()
+	pidFile.WriteString(strconv.FormatInt(int64(os.Getpid()), 10))
 	return sdNotify(ctx, sd.SdNotifyReady)
 }
 
 // notifyStopping notifies systemd that the daemon is about to be stopped
 func notifyStopping(ctx context.Context) error {
+	os.Remove("/run/containerd/containerd.pid")
 	return sdNotify(ctx, sd.SdNotifyStopping)
 }