daemon: move check for CPU-realtime daemon options

Perform the validation when the daemon starts instead of performing these
validations for each individual container, so that we can fail early.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

cmd/dockerd/config_unix.go

@@ -57,8 +57,8 @@ func installConfigFlags(conf *config.Config, flags *pflag.FlagSet) error {
 	flags.IntVar(&conf.OOMScoreAdjust, "oom-score-adjust", 0, "Set the oom_score_adj for the daemon")
 	flags.BoolVar(&conf.Init, "init", false, "Run an init in the container to forward signals and reap processes")
 	flags.StringVar(&conf.InitPath, "init-path", "", "Path to the docker-init binary")
-	flags.Int64Var(&conf.CPURealtimePeriod, "cpu-rt-period", 0, "Limit the CPU real-time period in microseconds for the parent cgroup for all containers")
-	flags.Int64Var(&conf.CPURealtimeRuntime, "cpu-rt-runtime", 0, "Limit the CPU real-time runtime in microseconds for the parent cgroup for all containers")
+	flags.Int64Var(&conf.CPURealtimePeriod, "cpu-rt-period", 0, "Limit the CPU real-time period in microseconds for the parent cgroup for all containers (not supported with cgroups v2)")
+	flags.Int64Var(&conf.CPURealtimeRuntime, "cpu-rt-runtime", 0, "Limit the CPU real-time runtime in microseconds for the parent cgroup for all containers (not supported with cgroups v2)")
 	flags.StringVar(&conf.SeccompProfile, "seccomp-profile", config.SeccompProfileDefault, `Path to seccomp profile. Use "unconfined" to disable the default seccomp profile`)
 	flags.Var(&conf.ShmSize, "default-shm-size", "Default shm size for containers")
 	flags.BoolVar(&conf.NoNewPrivileges, "no-new-privileges", false, "Set no-new-privileges by default for new containers")

cmd/dockerd/daemon.go

@@ -463,6 +463,11 @@ func loadDaemonCliConfig(opts *daemonOptions) (*config.Config, error) {
 		conf.TLSVerify = conf.TLS
 	}
 
+	err = validateCPURealtimeOptions(conf)
+	if err != nil {
+		return nil, err
+	}
+
 	return conf, nil
 }
 

cmd/dockerd/daemon_freebsd.go

@@ -1,5 +1,7 @@
 package main
 
+import "github.com/docker/docker/daemon/config"
+
 // preNotifyReady sends a message to the host when the API is active, but before the daemon is
 func preNotifyReady() {
 }
@@ -11,3 +13,7 @@ func notifyReady() {
 // notifyStopping sends a message to the host when the server is shutting down
 func notifyStopping() {
 }
+
+func validateCPURealtimeOptions(_ *config.Config) error {
+	return nil
+}

cmd/dockerd/daemon_linux.go

@@ -1,6 +1,12 @@
 package main
 
-import systemdDaemon "github.com/coreos/go-systemd/v22/daemon"
+import (
+	cdcgroups "github.com/containerd/cgroups"
+	systemdDaemon "github.com/coreos/go-systemd/v22/daemon"
+	"github.com/docker/docker/daemon/config"
+	"github.com/docker/docker/pkg/sysinfo"
+	"github.com/pkg/errors"
+)
 
 // preNotifyReady sends a message to the host when the API is active, but before the daemon is
 func preNotifyReady() {
@@ -16,3 +22,16 @@ func notifyReady() {
 func notifyStopping() {
 	go systemdDaemon.SdNotify(false, systemdDaemon.SdNotifyStopping)
 }
+
+func validateCPURealtimeOptions(config *config.Config) error {
+	if config.CPURealtimePeriod == 0 && config.CPURealtimeRuntime == 0 {
+		return nil
+	}
+	if cdcgroups.Mode() == cdcgroups.Unified {
+		return errors.New("daemon-scoped cpu-rt-period and cpu-rt-runtime are not implemented for cgroup v2")
+	}
+	if !sysinfo.New().CPURealtime {
+		return errors.New("daemon-scoped cpu-rt-period and cpu-rt-runtime are not supported by the kernel")
+	}
+	return nil
+}

cmd/dockerd/daemon_windows.go

@@ -97,3 +97,7 @@ func (cli *DaemonCli) initContainerD(_ context.Context) (func(time.Duration) err
 	system.InitContainerdRuntime(cli.Config.ContainerdAddr)
 	return nil, nil
 }
+
+func validateCPURealtimeOptions(_ *config.Config) error {
+	return nil
+}

daemon/oci_linux.go

@@ -818,16 +818,6 @@ func WithCgroups(daemon *Daemon, c *container.Container) coci.SpecOpts {
 			return nil
 		}
 
-		if cdcgroups.Mode() == cdcgroups.Unified {
-			return errors.New("daemon-scoped cpu-rt-period and cpu-rt-runtime are not implemented for cgroup v2")
-		}
-
-		// FIXME this is very expensive way to check if cpu rt is supported
-		sysInfo := daemon.RawSysInfo()
-		if !sysInfo.CPURealtime {
-			return errors.New("daemon-scoped cpu-rt-period and cpu-rt-runtime are not supported by the kernel")
-		}
-
 		p := cgroupsPath
 		if useSystemd {
 			initPath, err := cgroups.GetInitCgroup("cpu")