Clarify content of cloned / restored volumes

When cloning a volume or restoring a snapshot, the resulting volume should be
exact copy of the original volume. This includes any filesystem metadata.
Therefore, when the new volume is larger than the original one, the new
volume may need to resize the filesystem (ie call resize2fs, xfs_growfs, ...) to
make the bigger capacity available to workloads.

spec.md

@@ -725,7 +725,13 @@ Plugins MAY create 3 types of volumes:
 
 - Empty volumes. When plugin supports `CREATE_DELETE_VOLUME` OPTIONAL capability.
 - From an existing snapshot. When plugin supports `CREATE_DELETE_VOLUME` and `CREATE_DELETE_SNAPSHOT` OPTIONAL capabilities.
+  The Plugin SHOULD create a volume that looks like exact copy of the original snapshotted volume at the time the snapshot was taken.
+  If CO requests a volume that is larger than the original snapshotted volume, the Plugin can either refuse such a call with `OUT_OF_RANGE` error or SHOULD provide a volume that, when presented to a workload by `NodePublish` call, has both the requested (larger) size and contains data from the snapshot.
+  Explicitly, it's responsibility of the Plugin to resize the filesystem of the volume at or before `NodePublish` call, if the volume has `VolumeCapability` `MountVolume` and the filesystem resize is required to have the larger volume usable by the workload.
 - From an existing volume. When plugin supports cloning, and reports the OPTIONAL capabilities `CREATE_DELETE_VOLUME` and `CLONE_VOLUME`.
+  The Plugin SHOULD create a volume that looks like exact copy of the original volume.
+  If CO requests a volume that is larger than the original volume, the Plugin can either refuse such a call with `OUT_OF_RANGE` error or SHOULD provide a volume that, when presented to a workload by `NodePublish` call, has both the requested (larger) size and contains data from the original volume.
+  Explicitly, it's responsibility of the Plugin to resize the filesystem of the volume at or before `NodePublish` call, if the volume has `VolumeCapability` `MountVolume` and the filesystem resize is required to have the larger volume usable by the workload.
 
 ```protobuf
 message CreateVolumeRequest {
@@ -1161,7 +1167,7 @@ The CO MUST implement the specified error recovery behavior when it encounters t
 | Source does not exist | 5 NOT_FOUND | Indicates that the specified source does not exist. | Caller MUST verify that the `volume_content_source` is correct, the source is accessible, and has not been deleted before retrying with exponential back off. |
 | Volume already exists but is incompatible | 6 ALREADY_EXISTS | Indicates that a volume corresponding to the specified volume `name` already exists but is incompatible with the specified `capacity_range`, `volume_capabilities`, `parameters`, `accessibility_requirements` or `volume_content_source`. | Caller MUST fix the arguments or use a different `name` before retrying. |
 | Unable to provision in `accessible_topology` | 8 RESOURCE_EXHAUSTED | Indicates that although the `accessible_topology` field is valid, a new volume can not be provisioned with the specified topology constraints. More human-readable information MAY be provided in the gRPC `status.message` field. | Caller MUST ensure that whatever is preventing volumes from being provisioned in the specified location (e.g. quota issues) is addressed before retrying with exponential backoff. |
-| Unsupported `capacity_range` | 11 OUT_OF_RANGE | Indicates that the capacity range is not allowed by the Plugin, for example when trying to create a volume smaller than the source snapshot. More human-readable information MAY be provided in the gRPC `status.message` field. | Caller MUST fix the capacity range before retrying. |
+| Unsupported `capacity_range` | 11 OUT_OF_RANGE | Indicates that the capacity range is not allowed by the Plugin, for example when trying to create a volume smaller than the source snapshot or the Plugin does not support creating volumes larger than the source snapshot. More human-readable information MAY be provided in the gRPC `status.message` field. | Caller MUST fix the capacity range before retrying. |
 
 
 #### `DeleteVolume`