resmgr: write a PID file upon successful startup.

pkg/cri/resource-manager/flags.go

@@ -19,6 +19,7 @@ import (
 	"time"
 
 	"github.com/intel/cri-resource-manager/pkg/cri/resource-manager/sockets"
+	"github.com/intel/cri-resource-manager/pkg/pidfile"
 )
 
 // Options captures our command line parameters.
@@ -29,6 +30,7 @@ type options struct {
 	RelayDir            string
 	AgentSocket         string
 	ConfigSocket        string
+	PidFile             string
 	ResctrlPath         string
 	FallbackConfig      string
 	ForceConfig         string
@@ -58,7 +60,8 @@ func init() {
 		"local socket of the cri-resmgr agent to connect")
 	flag.StringVar(&opt.ConfigSocket, "config-socket", sockets.ResourceManagerConfig,
 		"Unix domain socket path where the resource manager listens for cri-resmgr-agent")
-
+	flag.StringVar(&opt.PidFile, "pid-file", pidfile.GetPath(),
+		"PID file to write daemon PID to")
 	flag.StringVar(&opt.FallbackConfig, "fallback-config", "",
 		"Fallback configuration to use unless/until one is available from the cache or agent.")
 	flag.StringVar(&opt.ForceConfig, "force-config", "",

pkg/cri/resource-manager/resource-manager.go

@@ -36,6 +36,7 @@ import (
 	"github.com/intel/cri-resource-manager/pkg/cri/resource-manager/visualizer"
 	"github.com/intel/cri-resource-manager/pkg/instrumentation"
 	logger "github.com/intel/cri-resource-manager/pkg/log"
+	"github.com/intel/cri-resource-manager/pkg/pidfile"
 
 	policyCollector "github.com/intel/cri-resource-manager/pkg/policycollector"
 	"github.com/intel/cri-resource-manager/pkg/utils"
@@ -118,6 +119,10 @@ func NewResourceManager() (ResourceManager, error) {
 	}
 
 	if err := m.setupRelay(); err != nil {
+		pid, _ := pidfile.OwnerPid()
+		if pid > 0 {
+			m.Error("looks like we're already running as pid %d...", pid)
+		}
 		return nil, err
 	}
 
@@ -165,6 +170,13 @@ func (m *resmgr) Start() error {
 		return resmgrError("failed to start CRI relay: %v", err)
 	}
 
+	if err := pidfile.Remove(); err != nil {
+		return resmgrError("failed to remove stale/old PID file: %v", err)
+	}
+	if err := pidfile.Write(); err != nil {
+		return resmgrError("failed to write PID file: %v", err)
+	}
+
 	if opt.ForceConfig == "" {
 		if err := m.configServer.Start(opt.ConfigSocket); err != nil {
 			return resmgrError("failed to start configuration server: %v", err)