Merge pull request #316 from saad-ali/clarifyInvalidArgument

Clarify InvalidArgument details

Author: saad-ali

spec.md

@@ -404,7 +404,7 @@ The status `code` MUST contain a [canonical error code](https://github.com/grpc/
 
 | Condition | gRPC Code | Description | Recovery Behavior |
 |-----------|-----------|-------------|-------------------|
-| Missing required field | 3 INVALID_ARGUMENT | Indicates that a required field is missing from the request. More human-readable information MAY be provided in the `error_description` field. | Caller MUST fix the request by adding the missing required field before retrying. |
+| Missing required field | 3 INVALID_ARGUMENT | Indicates that a required field is missing from the request. More human-readable information MAY be provided in the `status.message` field. | Caller MUST fix the request by adding the missing required field before retrying. |
 | Invalid or unsupported field in the request | 3 INVALID_ARGUMENT | Indicates that the one ore more fields in this field is either not allowed by the Plugin or has an invalid value. More human-readable information MAY be provided in the gRPC `status.message` field. | Caller MUST fix the field before retrying. |
 | Permission denied | 7 PERMISSION_DENIED | The Plugin is able to derive or otherwise infer an identity from the secrets present within an RPC, but that identity does not have permission to invoke the RPC. | System administrator SHOULD ensure that requisite permissions are granted, after which point the caller MAY retry the attempted RPC. |
 | Operation pending for volume | 10 ABORTED | Indicates that there is already an operation pending for the specified volume. In general the Cluster Orchestrator (CO) is responsible for ensuring that there is no more than one call "in-flight" per volume at a given time. However, in some circumstances, the CO MAY lose state (for example when the CO crashes and restarts), and MAY issue multiple calls simultaneously for the same volume. The Plugin, SHOULD handle this as gracefully as possible, and MAY return this error code to reject secondary calls. | Caller SHOULD ensure that there are no other calls pending for the specified volume, and then retry with exponential back off. |