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Merge pull request #605 from carlbraganza/snapshot-metadata-sidecar-alpha
Documentation on the external-snaphot-metadata sidecar (alpha).
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‎book/src/SUMMARY.md

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- [cluster-driver-registrar](cluster-driver-registrar.md) (deprecated)
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- [external-health-monitor-controller](external-health-monitor-controller.md)
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- [external-health-monitor-agent](external-health-monitor-agent.md)
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- [external-snapshot-metadata](external-snapshot-metadata.md)
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- [CSI objects](csi-objects.md)
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- [CSIDriver Object](csi-driver-object.md)
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- [CSINode Object](csi-node-object.md)
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- [CSI Windows](csi-windows.md)
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- [Volume Mode Conversion](prevent-volume-mode-conversion.md)
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- [Cross-Namespace Data Sources](cross-namespace-data-sources.md)
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- [Changed Block Tracking](changed-block-tracking.md)
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- [Deploying a CSI Driver on Kubernetes](deploying.md)
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- [Example](example.md)
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- [Driver Testing](testing-drivers.md)

‎book/src/changed-block-tracking.md

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# Changed Block Tracking
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## Status
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Status | Min K8s Version | Max K8s Version | Min CSI Version | Max CSI Version |
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-------|-----------------|-----------------|-----------------|-----------------|
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Alpha | 1.33 | - | [v1.10.0](https://github.com/container-storage-interface/spec/releases/tag/v1.10.0) | -
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## Overview
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This optional feature provides a secure mechanism to obtain metadata
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on the allocated blocks of a CSI VolumeSnapshot, or the changed blocks between two arbitrary pairs of CSI VolumeSnapshot objects of the same PersistentVolume.
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See [Kubernetes Enhancement Proposal 3314](https://github.com/kubernetes/enhancements/tree/master/keps/sig-storage/3314-csi-changed-block-tracking)
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for full details.
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A CSI driver must advertise its support for this feature by specifying the
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`SNAPSHOT_METADATA_SERVICE` capability in the response of the
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[GetPluginCapabilities](https://github.com/container-storage-interface/spec/blob/master/spec.md#getplugincapabilities)
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RPC (part of the
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[CSI Identity Service](https://github.com/container-storage-interface/spec/blob/master/spec.md#identity-service-rpc)),
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and must implement the
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[CSI SnapshotMetadata Service](https://github.com/container-storage-interface/spec/blob/master/spec.md#snapshot-metadata-service-rpcs).
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CSI drivers that implement this feature should deploy the
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[external-snapshot-metadata](./external-snapshot-metadata.md)
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sidecar and create the associated
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[Snapshot Metadata Service CR](https://github.com/kubernetes/enhancements/tree/master/keps/sig-storage/3314-csi-changed-block-tracking#snapshot-metadata-service-custom-resource).
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The `external-snapshot-metadata` sidecar implements the server side of the
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[Kubernetes SnapshotMetadata Service API](https://github.com/kubernetes/enhancements/tree/master/keps/sig-storage/3314-csi-changed-block-tracking#the-kubernetes-snapshotmetadata-service-api).
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Backup applications obtain VolumeSnapshot metadata directly from the sidecar
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through this API, bypassing the Kubernetes API server for the most part.
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Backup application developers should refer to the [Usage](external-snapshot-metadata.md#usage)
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and [Resources](external-snapshot-metadata.md#resources)
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sections of the sidecar documentation for details.
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‎book/src/example.md

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The example deployment uses the original RBAC rule files that are maintained together with sidecar apps and deploys into the default namespace. A real production should copy the RBAC files and customize them as explained in the comments of those files.
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The Hostpath CSI driver only supports the [Changed Block Tracking](./changed-block-tracking.md) feature for
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PersistentVolumes with `Block` VolumeMode.
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The support is not enabled by default, but requires additional configuration when deploying the driver.
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When enabled, the
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[external-snapshot-metadata](./external-snapshot-metadata.md)
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sidecar will also be deployed, and the additional RBAC policies needed will get created.
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See the [docs/example-snapshot-metadata.md](https://github.com/kubernetes-csi/csi-driver-host-path/blob/master/docs/example-snapshot-metadata.md)
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document for details.
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If you encounter any problems, please check the [Troubleshooting page](troubleshooting.html).

‎book/src/external-snapshot-metadata.md

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# CSI external-snapshot-metadata
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## Status and Releases
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**Git Repository:** [https://github.com/kubernetes-csi/external-snapshot-metadata](https://github.com/kubernetes-csi/external-snapshot-metadata)
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### Supported Versions
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Latest stable release | Branch | Min CSI Version | Max CSI Version | Container Image | [Min K8s Version](project-policies.md#minimum-version) | [Max K8s Version](project-policies.md#maximum-version) | [Recommended K8s Version](project-policies.md#recommended-version) |
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--|--|--|--|--|--|--|--
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v0.1.0 | [v0.1.0](https://github.com/kubernetes-csi/external-snapshot-metadata/releases/tag/v0.1.0) | [v1.10.0](https://github.com/container-storage-interface/spec/releases/tag/v1.10.0) | - | registry.k8s.io/sig-storage/csi-snapshot-metadata:v0.1.0 | v1.33 | - | v1.33
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## Alpha
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### Description
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This sidecar securely serves snapshot metadata to Kubernetes clients through the
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[Kubernetes SnapshotMetadata Service API](https://github.com/kubernetes/enhancements/tree/master/keps/sig-storage/3314-csi-changed-block-tracking#the-kubernetes-snapshotmetadata-service-api).
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This API is similar to the
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[CSI SnapshotMetadata Service](https://github.com/container-storage-interface/spec/blob/master/spec.md#snapshot-metadata-service-rpcs)
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but is designed to be used by Kuberetes authenticated and authorized backup applications.
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Its [protobuf specification](https://github.com/kubernetes-csi/external-snapshot-metadata/tree/main/proto/schema.proto)
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is available in the sidecar repository.
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The sidecar authenticates and authorizes each Kubernetes backup application request made through the
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Kubernetes SnapshotMetadata Service API.
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It then acts as a proxy as it fetches the desired metadata from the CSI driver and
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streams it directly to the requesting application with no load on the Kubernetes API server.
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See ["The External Snapshot Metadata Sidecar"](https://github.com/kubernetes/enhancements/tree/master/keps/sig-storage/3314-csi-changed-block-tracking#the-external-snapshot-metadata-sidecar)
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section in the CSI Changed Block Tracking KEP for additional details on the sidecar.
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### Usage
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Backup applications, identified by their authorized ServiceAccount objects,
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directly communicate with the sidecar using the
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[Kubernetes SnapshotMetadata Service API](https://github.com/kubernetes/enhancements/tree/master/keps/sig-storage/3314-csi-changed-block-tracking#the-kubernetes-snapshotmetadata-service-api).
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The authorization needed is described in the
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["Risks and Mitigations"](https://github.com/kubernetes/enhancements/tree/master/keps/sig-storage/3314-csi-changed-block-tracking#risks-and-mitigations)
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section of the CSI Changed Block Tracking KEP.
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In particular, this requires the ability to use the Kubernetes
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[TokenRequest](https://kubernetes.io/docs/reference/kubernetes-api/authentication-resources/token-request-v1/)
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API and to access the objects required to use the API.
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The availability of this optional feature is advertised to backup applications by the presence of a
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[Snapshot Metadata Service CR](https://github.com/kubernetes/enhancements/tree/master/keps/sig-storage/3314-csi-changed-block-tracking#snapshot-metadata-service-custom-resource)
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that is named for the CSI driver that provisioned the PersistentVolume and VolumeSnapshot objects involved.
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The CR contains a gRPC service endpoint and CA certificate, and an audience string for authentication.
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A backup application must use the Kubernetes
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[TokenRequest](https://kubernetes.io/docs/reference/kubernetes-api/authentication-resources/token-request-v1/)
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API with the audience string to obtain a Kubernetes authentication token for use in the
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Kubernetes SnapshotMetadata Service API call.
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The backup application should establish trust for the CA certificate before making the gRPC call
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to the service endpoint.
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The Kubernetes SnapshotMetadata Service API uses a gRPC stream to return VolumeSnapshot metadata
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to the backup application. Metadata can be lengthy, so the API supports
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restarting an interrupted metadata request from an intermediate point in case of failure.
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The [Resources](external-snapshot-metadata.md#resources) section below describes the
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programming artifacts available to support backup application use of this API.
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### Deployment
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The CSI `external-snapshot-metadata` sidecar should be deployed by
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CSI drivers that support the
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[Changed Block Tracking](./changed-block-tracking.md) feature.
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The sidecar must be deployed in the same pod as the CSI driver and
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will communicate with its gRPC [CSI SnapshotMetadata Service](https://github.com/container-storage-interface/spec/blob/master/spec.md#snapshot-metadata-service-rpcs)
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and [CSI Identity Service](https://github.com/container-storage-interface/spec/blob/master/spec.md#identity-service-rpc)
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over a UNIX domain socket.
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The sidecar should be configured to run under the authority of its
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CSI driver ServiceAccount, which must be authorized as described in the
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["Risks and Mitigations"](https://github.com/kubernetes/enhancements/tree/master/keps/sig-storage/3314-csi-changed-block-tracking#risks-and-mitigations)
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section of the CSI Changed Block Tracking KEP.
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In particular, this requires the ability to use the Kubernetes
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[TokenReview](https://kubernetes.io/docs/reference/kubernetes-api/authentication-resources/token-review-v1/)
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and
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[SubjectAccessReview](https://kubernetes.io/docs/reference/kubernetes-api/authorization-resources/subject-access-review-v1/)
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APIs.
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A Service object must be created to expose the endpoints of the
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[Kubernetes SnapshotMetadata Service API](https://github.com/kubernetes/enhancements/tree/master/keps/sig-storage/3314-csi-changed-block-tracking#the-kubernetes-snapshotmetadata-service-api)
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gRPC server implemented by the sidecar.
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A [SnapshotMetadataService CR](https://github.com/kubernetes/enhancements/tree/master/keps/sig-storage/3314-csi-changed-block-tracking#snapshot-metadata-service-custom-resource),
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named for the CSI driver, must be created to advertise the
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availability of this optional feature to Kubernetes backup application clients.
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The CR contains the CA certificate and Service endpoint address
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of the sidecar and the audience string needed for the client
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authentication token.
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### Resources
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The [external-snapshot-metadata repository](https://github.com/kubernetes-csi/external-snapshot-metadata) contains
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the [protobuf specification](https://github.com/kubernetes-csi/external-snapshot-metadata/tree/main/proto/schema.proto)
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of the
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[Kubernetes SnapshotMetadata Service API](https://github.com/kubernetes/enhancements/tree/master/keps/sig-storage/3314-csi-changed-block-tracking#the-kubernetes-snapshotmetadata-service-api).
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In addition, the repository has a number of useful artifacts to support Go language programs:
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- The
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[Go client interface](https://github.com/kubernetes-csi/external-snapshot-metadata/tree/main/client)
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for the Kubernetes SnapshotMetadata Service API.
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- The
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[pkg/iterator](https://github.com/kubernetes-csi/external-snapshot-metadata/tree/main/pkg/iterator)
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client helper package.
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This may be used by backup applications instead of working directly with the
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Kubernetes SnapshotMetadata Service gRPC client interfaces.
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The
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[snapshot-metadata-lister](https://github.com/kubernetes-csi/external-snapshot-metadata/tree/main/examples/snapshot-metadata-lister)
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example Go command illustrates the use of this helper package.
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- Go language
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[CSI SnapshotMetadataService API client mocks](https://github.com/kubernetes-csi/external-snapshot-metadata/tree/main/pkg/csiclientmocks).
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The sample [Hostpath CSI driver](example.md) has been extended to support the
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[Changed Block Tracking](./changed-block-tracking.md) feature
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and provides an illustration on how to deploy a CSI driver.

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