The following APIs are yet not supported by the Terraform provider

1. POST /v1/volumes/{uuid}/revert
2. GET /v1/volume-snapshots?{query_string}
3. GET /v1/volume-snapshots/{uuid}
4. POST /v1/volume-snapshots
5. PATCH /v1/volume-snapshots/{uuid}
6. DELETE /v1/volume-snapshots/{uuid}

Are you planning to release a new version of the provider to include them? I fear that invoking these APIs using a null_resource will not be the best idea.

resource "null_resource" "cloudscale-shapshot-create" {
  provisioner "local-exec" {
      command = "$ curl -i -H "$AUTH_HEADER" -F name="pre-dist-upgrade" -F source_volume="<VOLUME-ID>" https://api.cloudscale.ch/v1/volume-snapshots"
  }
}