Change devicemanager to implement HintProvider.Allocate()

This change will not work on its own. Higher level code needs to make
sure and call Allocate() before AddContainer is called. This is already
being done in cases when the TopologyManager feature gate is enabled (in
the PodAdmitHandler of the TopologyManager). However, we need to make
sure we add proper logic to call it in cases when the TopologyManager
feature gate is disabled.

Author: klueska

pkg/kubelet/cm/devicemanager/manager.go

@@ -369,10 +369,30 @@ func (m *ManagerImpl) allocatePodResources(pod *v1.Pod) error {
 
 // Allocate is the call that you can use to allocate a set of devices
 // from the registered device plugins.
-func (m *ManagerImpl) Allocate(pod *v1.Pod) error {
+func (m *ManagerImpl) Allocate(pod *v1.Pod, container *v1.Container) error {
+	// TODO: This function does not yet do what it is supposed to. The call to
+	// allocatePodResources() below is still allocating devices to a pod all at
+	// once. We need to unroll this logic to allow it to allocate devices on a
+	// container-by-container basis instead. The main challenge will be
+	// ensuring that we "reuse" devices from init containers when allocating
+	// devices to app containers (just as the logic inside
+	// allocatePodResources() currently does). The hard part being that we will
+	// need to maintain the 'devicesToReuse' present in allocatePodResources()
+	// across invocations of Allocate().
+	//
+	// My initial inclination to solve this with the least coode churn is:
+	//   1) Create a new type called PodReusableDevices, defined as:
+	//			type PodReusableDevices map[string]map[string]sets.String
+	//   2) Instantiate a PodReusableDevices map as a new field of the
+	//      devicemanager called devicesToReuse (similar to the local
+	//      devicesToReuse variable currently in allocatePodResources)
+	//   3) Use devicesToReuse[string(pod.UID) just as devicesToReuse is used
+	//      today, being careful to create / destroy the nested maps where
+	//      appropriate.
+
 	err := m.allocatePodResources(pod)
 	if err != nil {
-		klog.Errorf("Failed to allocate device plugin resource for pod %s: %v", string(pod.UID), err)
+		klog.Errorf("Failed to allocate device plugin resource for pod %s, container %s: %v", string(pod.UID), container.Name, err)
 		return err
 	}
 	return nil
@@ -864,8 +884,8 @@ func (m *ManagerImpl) GetDeviceRunContainerOptions(pod *v1.Pod, container *v1.Co
 		}
 	}
 	if needsReAllocate {
-		klog.V(2).Infof("needs re-allocate device plugin resources for pod %s", podUID)
-		if err := m.allocatePodResources(pod); err != nil {
+		klog.V(2).Infof("needs re-allocate device plugin resources for pod %s, container %s", podUID, container.Name)
+		if err := m.Allocate(pod, container); err != nil {
 			return nil, err
 		}
 	}

pkg/kubelet/cm/devicemanager/manager_stub.go

@@ -45,7 +45,7 @@ func (h *ManagerStub) Stop() error {
 }
 
 // Allocate simply returns nil.
-func (h *ManagerStub) Allocate(pod *v1.Pod) error {
+func (h *ManagerStub) Allocate(pod *v1.Pod, container *v1.Container) error {
 	return nil
 }
 

pkg/kubelet/cm/devicemanager/types.go

@@ -34,12 +34,12 @@ type Manager interface {
 	// Start starts device plugin registration service.
 	Start(activePods ActivePodsFunc, sourcesReady config.SourcesReady) error
 
-	// Allocate configures and assigns devices to a pod. From the requested
-	// device resources, Allocate will communicate with the owning device
-	// plugin to allow setup procedures to take place, and for the device
-	// plugin to provide runtime settings to use the device (environment
-	// variables, mount points and device files).
-	Allocate(pod *v1.Pod) error
+	// Allocate configures and assigns devices to a container in a pod. From
+	// the requested device resources, Allocate will communicate with the
+	// owning device plugin to allow setup procedures to take place, and for
+	// the device plugin to provide runtime settings to use the device
+	// (environment variables, mount points and device files).
+	Allocate(pod *v1.Pod, container *v1.Container) error
 
 	// UpdatePluginResources updates node resources based on devices already
 	// allocated to pods. The node object is provided for the device manager to