Support online and offline expansion without requiring them to be declared in plugin capabilities.

Ability for a plugin to delcare online and offline controller expansion
capabilities via GetPluginCapabilities is deprecated. A plugin may
support either mode of operation without having to declare them
in GetPluginCapabilities call.

If a plugin can not support controller expansion of published volume
it may return Volume-in-use error and CO should ensure that volume is
not published before retrying with exponential backoff.

Author: gnufied

spec.md

@@ -625,7 +625,7 @@ message PluginCapability {
       ONLINE = 1;
 
       // OFFLINE indicates that volumes currently published and
-      // available on a node SHALL NOT be expanded via
+      // available on a node SHOULD NOT be expanded via
       // ControllerExpandVolume. When a plugin supports OFFLINE volume
       // expansion it MUST implement either the EXPAND_VOLUME controller
       // capability or both the EXPAND_VOLUME controller capability and
@@ -644,6 +644,7 @@ message PluginCapability {
   oneof type {
     // Service that the plugin supports.
     Service service = 1;
+    // deprecated
     VolumeExpansion volume_expansion = 2;
   }
 }
@@ -1930,24 +1931,15 @@ This RPC allows the CO to expand the size of a volume.
 This operation MUST be idempotent.
 If a volume corresponding to the specified volume ID is already larger than or equal to the target capacity of the expansion request, the plugin SHOULD reply 0 OK.
 
-This call MAY be made by the CO during any time in the lifecycle of the volume after creation if plugin has `VolumeExpansion.ONLINE` capability.
+This call MAY be made by the CO during any time in the lifecycle of the volume after creation but an SP may not permit controller expansion of volumes which are controller published or available on a node. In which case - the plugin may return gRPC error code`FAILED_PRECONDITION` (Volume in use) and CO SHOULD ensure that volume is not published and retry with exponential backoff.
+
 If plugin has `EXPAND_VOLUME` node capability, then `NodeExpandVolume` MUST be called after successful `ControllerExpandVolume` and `node_expansion_required` in `ControllerExpandVolumeResponse` is `true`.
 
 If specified, the `volume_capability` in `ControllerExpandVolumeRequest` should be same as what CO would pass in `ControllerPublishVolumeRequest`.
 
-If the plugin has only `VolumeExpansion.OFFLINE` expansion capability and volume is currently published or available on a node then `ControllerExpandVolume` MUST be called ONLY after either:
-- The plugin has controller `PUBLISH_UNPUBLISH_VOLUME` capability and `ControllerUnpublishVolume` has been invoked successfully.
-
-OR ELSE
-
-- The plugin does NOT have controller `PUBLISH_UNPUBLISH_VOLUME` capability, the plugin has node `STAGE_UNSTAGE_VOLUME` capability, and `NodeUnstageVolume` has been completed successfully.
-
-OR ELSE
-
-- The plugin does NOT have controller `PUBLISH_UNPUBLISH_VOLUME` capability, nor node `STAGE_UNSTAGE_VOLUME` capability, and `NodeUnpublishVolume` has completed successfully.
 
 Examples:
-* Offline Volume Expansion:
+* Offline Volume Expansion(SP does not permit controller expansion of controller published volume):
   Given an ElasticSearch process that runs on Azure Disk and needs more space.
   - The administrator takes the Elasticsearch server offline by stopping the workload and CO calls `ControllerUnpublishVolume`.
   - The administrator requests more space for the volume from CO.
@@ -2003,7 +1995,7 @@ message ControllerExpandVolumeResponse {
 |-----------|-----------|-------------|-------------------|
 | Exceeds capabilities | 3 INVALID_ARGUMENT | Indicates that CO has specified capabilities not supported by the volume. | Caller MAY verify volume capabilities by calling ValidateVolumeCapabilities and retry with matching capabilities. |
 | Volume does not exist | 5 NOT FOUND | Indicates that a volume corresponding to the specified volume_id does not exist. | Caller MUST verify that the volume_id is correct and that the volume is accessible and has not been deleted before retrying with exponential back off. |
-| Volume in use | 9 FAILED_PRECONDITION | Indicates that the volume corresponding to the specified `volume_id` could not be expanded because it is currently published on a node but the plugin does not have ONLINE expansion capability. | Caller SHOULD ensure that volume is not published and retry with exponential back off. |
+| Volume in use | 9 FAILED_PRECONDITION | Indicates that the volume corresponding to the specified `volume_id` could not be expanded because it is currently published on a node. | Caller SHOULD ensure that volume is not published and retry with exponential back off. |
 | Unsupported `capacity_range` | 11 OUT_OF_RANGE | Indicates that the capacity range is not allowed by the Plugin. More human-readable information MAY be provided in the gRPC `status.message` field. | Caller MUST fix the capacity range before retrying. |
 
 #### RPC Interactions
@@ -2523,8 +2515,6 @@ If plugin has `STAGE_UNSTAGE_VOLUME` node capability then:
 
 Otherwise `NodeExpandVolume` MUST be called after successful `NodePublishVolume`.
 
-If a plugin only supports expansion via the `VolumeExpansion.OFFLINE` capability, then the volume MUST first be taken offline and expanded via `ControllerExpandVolume` (see `ControllerExpandVolume` for more details), and then node-staged or node-published before it can be expanded on the node via `NodeExpandVolume`.
-
 The `staging_target_path` field is not required, for backwards compatibility, but the CO SHOULD supply it.
 Plugins can use this field to determine if `volume_path` is where the volume is published or staged,
 and setting this field to non-empty allows plugins to function with less stored state on the node.