csi: provide `CSI_ENDPOINT` env var to plugins (#12050)

The CSI specification says:
> The CO SHALL provide the listen-address for the Plugin by way of the
`CSI_ENDPOINT` environment variable.

Note that plugins without filesystem isolation won't have the plugin
dir bind-mounted to their alloc dir, but we can provide a path to the
socket anyways.

Refactor to use opts struct for plugin supervisor hook config.
The parameter list for configuring the plugin supervisor hook has
grown enough where is makes sense to use an options struct similiar to
many of the other task runner hooks (ex. template).

.changelog/12050.txt

@@ -0,0 +1,3 @@
+```release-note:bug
+csi: provide `CSI_ENDPOINT` environment variable to plugin tasks
+```

client/allocrunner/taskrunner/plugin_supervisor_hook.go

@@ -34,6 +34,8 @@ type csiPluginSupervisorHook struct {
 	runner     *TaskRunner
 	mountPoint string
 
+	caps *drivers.Capabilities
+
 	// eventEmitter is used to emit events to the task
 	eventEmitter ti.EventEmitter
 
@@ -48,6 +50,14 @@ type csiPluginSupervisorHook struct {
 	previousHealthState bool
 }
 
+type csiPluginSupervisorHookConfig struct {
+	clientStateDirPath string
+	events             ti.EventEmitter
+	runner             *TaskRunner
+	capabilities       *drivers.Capabilities
+	logger             hclog.Logger
+}
+
 // The plugin supervisor uses the PrestartHook mechanism to setup the requisite
 // mount points and configuration for the task that exposes a CSI plugin.
 var _ interfaces.TaskPrestartHook = &csiPluginSupervisorHook{}
@@ -61,8 +71,8 @@ var _ interfaces.TaskPoststartHook = &csiPluginSupervisorHook{}
 // with the catalog and to ensure any mounts are cleaned up.
 var _ interfaces.TaskStopHook = &csiPluginSupervisorHook{}
 
-func newCSIPluginSupervisorHook(csiRootDir string, eventEmitter ti.EventEmitter, runner *TaskRunner, logger hclog.Logger) *csiPluginSupervisorHook {
-	task := runner.Task()
+func newCSIPluginSupervisorHook(config *csiPluginSupervisorHookConfig) *csiPluginSupervisorHook {
+	task := config.runner.Task()
 
 	// The Plugin directory will look something like this:
 	// .
@@ -72,19 +82,21 @@ func newCSIPluginSupervisorHook(csiRootDir string, eventEmitter ti.EventEmitter,
 	//  {volume-id}/{usage-mode-hash}/ - Intermediary mount point that will be used by plugins that support NODE_STAGE_UNSTAGE capabilities.
 	// per-alloc/
 	//  {alloc-id}/{volume-id}/{usage-mode-hash}/ - Mount Point that will be bind-mounted into tasks that utilise the volume
-	pluginRoot := filepath.Join(csiRootDir, string(task.CSIPluginConfig.Type), task.CSIPluginConfig.ID)
+	pluginRoot := filepath.Join(config.clientStateDirPath, "csi",
+		string(task.CSIPluginConfig.Type), task.CSIPluginConfig.ID)
 
 	shutdownCtx, cancelFn := context.WithCancel(context.Background())
 
 	hook := &csiPluginSupervisorHook{
-		alloc:            runner.Alloc(),
-		runner:           runner,
-		logger:           logger,
+		alloc:            config.runner.Alloc(),
+		runner:           config.runner,
+		logger:           config.logger,
 		task:             task,
 		mountPoint:       pluginRoot,
+		caps:             config.capabilities,
 		shutdownCtx:      shutdownCtx,
 		shutdownCancelFn: cancelFn,
-		eventEmitter:     eventEmitter,
+		eventEmitter:     config.events,
 	}
 
 	return hook
@@ -119,6 +131,20 @@ func (h *csiPluginSupervisorHook) Prestart(ctx context.Context,
 		Readonly: false,
 	}
 
+	switch h.caps.FSIsolation {
+	case drivers.FSIsolationNone:
+		// Plugin tasks with no filesystem isolation won't have the
+		// plugin dir bind-mounted to their alloc dir, but we can
+		// provide them the path to the socket. These Nomad-only
+		// plugins will need to be aware of the csi directory layout
+		// in the client data dir
+		resp.Env = map[string]string{
+			"CSI_ENDPOINT": filepath.Join(h.mountPoint, "csi.sock")}
+	default:
+		resp.Env = map[string]string{
+			"CSI_ENDPOINT": filepath.Join(h.task.CSIPluginConfig.MountDir, "csi.sock")}
+	}
+
 	mounts := ensureMountpointInserted(h.runner.hookResources.getMounts(), configMount)
 	mounts = ensureMountpointInserted(mounts, devMount)
 

client/allocrunner/taskrunner/task_runner_hooks.go

@@ -3,7 +3,6 @@ package taskrunner
 import (
 	"context"
 	"fmt"
-	"path/filepath"
 	"sync"
 	"time"
 
@@ -72,7 +71,14 @@ func (tr *TaskRunner) initHooks() {
 
 	// If the task has a CSI stanza, add the hook.
 	if task.CSIPluginConfig != nil {
-		tr.runnerHooks = append(tr.runnerHooks, newCSIPluginSupervisorHook(filepath.Join(tr.clientConfig.StateDir, "csi"), tr, tr, hookLogger))
+		tr.runnerHooks = append(tr.runnerHooks, newCSIPluginSupervisorHook(
+			&csiPluginSupervisorHookConfig{
+				clientStateDirPath: tr.clientConfig.StateDir,
+				events:             tr,
+				runner:             tr,
+				capabilities:       tr.driverCapabilities,
+				logger:             hookLogger,
+			}))
 	}
 
 	// If Vault is enabled, add the hook