Add document for Cross namespace data sources

Author: ttakahashi21

content/en/docs/concepts/storage/persistent-volumes.md

@@ -952,6 +952,18 @@ or to a VolumeSnapshot, the `dataSourceRef` field can contain a reference to any
 same namespace, except for core objects other than PVCs. For clusters that have the feature
 gate enabled, use of the `dataSourceRef` is preferred over `dataSource`.
 
+## Cross namespace data sources
+{{< feature-state for_k8s_version="v1.26" state="alpha" >}}
+
+Kubernetes supports cross namespace volume data source.
+To use cross namespace volume datasource, you must enable the `AnyVolumeDataSource` and `CrossNamespaceVolumeDataSource`
+[feature gate](/docs/reference/command-line-tools-reference/feature-gates/) for
+the kube-apiserver, kube-controller-manager.
+Also, you must enable the `CrossNamespaceVolumeDataSource` feature gate for csi-provisioner.
+
+Enabling the `CrossNamespaceVolumeDataSource` feature gate allow you to specify a namespace in the dataSourceRef field.
+{{< note >}}  When a namespace is specified, a gateway.networking.k8s.io/ReferenceGrant object is required in the referent namespace to allow that namespace's owner to accept the reference. See the [ReferenceGrant documentation](https://gateway-api.sigs.k8s.io/api-types/referencegrant/) for details.
+
 ## Data source references
 
 The `dataSourceRef` field behaves almost the same as the `dataSource` field. If either one is
@@ -969,6 +981,11 @@ users should be aware of:
 * The `dataSourceRef` field may contain different types of objects, while the `dataSource` field
   only allows PVCs and VolumeSnapshots.
 
+When the `CrossNamespaceVolumeDataSource` feature is enabled, there are additional differences:
+
+* The `dataSource` field only allows local objects, while the `dataSourceRef` field allows objects in any namespaces.  
+* When namespace is specified, `dataSource` and `dataSourceRef` are not synced.
+
 Users should always use `dataSourceRef` on clusters that have the feature gate enabled, and
 fall back to `dataSource` on clusters that do not. It is not necessary to look at both fields
 under any circumstance. The duplicated values with slightly different semantics exist only for
@@ -1009,6 +1026,50 @@ is registered to handle that kind of data source. When a suitable populator is i
 responsibility of that populator controller to report Events that relate to volume creation and issues during
 the process.
 
+### Using Cross Namespace Volume Data Source
+{{< feature-state for_k8s_version="v1.26" state="alpha" >}}
+
+Create a gateway.networking.k8s.io/ReferenceGrant to allow the namespace owner to accept the reference.
+Users create a populated volume by referring cross namespace volume data source using the `dataSourceRef` field:
+
+   ```yaml
+   apiVersion: gateway.networking.k8s.io/v1beta1
+   kind: ReferenceGrant
+   metadata:
+     name: allow-ns1-pvcg
+     namespace: default
+   spec:
+     from:
+     - group: ""
+       kind: PersistentVolumeClaim
+       namespace: ns1
+     to:
+     - group: snapshot.storage.k8s.io
+       kind: VolumeSnapshot
+       name: new-snapshot-demo
+   ```
+
+   ```yaml
+   apiVersion: v1
+   kind: PersistentVolumeClaim
+   metadata:
+     name: foo-pvc
+     namespace: ns1
+   spec:
+     storageClassName: example
+     accessModes:
+     - ReadWriteOnce
+     resources:
+       requests:
+         storage: 1Gi
+     dataSourceRef:
+       apiGroup: snapshot.storage.k8s.io
+       kind: VolumeSnapshot
+       name: new-snapshot-demo
+       namespace: default
+     volumeMode: Filesystem
+   ```
+
 ## Writing Portable Configuration
 
 If you're writing configuration templates or examples that run on a wide range of clusters

content/en/docs/reference/command-line-tools-reference/feature-gates.md

@@ -72,6 +72,7 @@ For a reference to old feature gates that are removed, please refer to
 | `CPUManagerPolicyBetaOptions` | `true` | Beta | 1.23 | |
 | `CPUManagerPolicyOptions` | `false` | Alpha | 1.22 | 1.22 |
 | `CPUManagerPolicyOptions` | `true` | Beta | 1.23 | |
+| `CrossNamespaceVolumeDataSource` | `false` | Alpha| 1.26 | |
 | `CSIMigrationPortworx` | `false` | Alpha | 1.23 | 1.24 |
 | `CSIMigrationPortworx` | `false` | Beta | 1.25 | |
 | `CSIMigrationRBD` | `false` | Alpha | 1.23 | |
@@ -410,6 +411,8 @@ Each feature gate is designed for enabling/disabling a specific feature:
   This feature gate guards *a group* of CPUManager options whose quality level is beta.
   This feature gate will never graduate to stable.
 - `CPUManagerPolicyOptions`: Allow fine-tuning of CPUManager policies.
+- `CrossNamespaceVolumeDataSource`: Enable the usage of cross namespace volume data source
+   to allow you to specify a namespace in the dataSourceRef field.
 - `CSIInlineVolume`: Enable CSI Inline volumes support for pods.
 - `CSIMigration`: Enables shims and translation logic to route volume
   operations from in-tree plugins to corresponding pre-installed CSI plugins
@@ -747,4 +750,4 @@ Each feature gate is designed for enabling/disabling a specific feature:
   feature, you will also need to enable any associated API resources.
   For example, to enable a particular resource like
   `storage.k8s.io/v1beta1/csistoragecapacities`, set `--runtime-config=storage.k8s.io/v1beta1/csistoragecapacities`.
-  See [API Versioning](/docs/reference/using-api/#api-versioning) for more details on the command line flags.
+  See [API Versioning](/docs/reference/using-api/#api-versioning) for more details on the command line flags.