[platform] add device_control env var (#12009)

Signed-off-by: youkaichao <youkaichao@gmail.com>

vllm/platforms/interface.py

@@ -78,20 +78,30 @@ class Platform:
     _enum: PlatformEnum
     device_name: str
     device_type: str
+
     # available dispatch keys:
     # check https://github.com/pytorch/pytorch/blob/313dac6c1ca0fa0cde32477509cce32089f8532a/torchgen/model.py#L134 # noqa
     # use "CPU" as a fallback for platforms not registered in PyTorch
     dispatch_key: str = "CPU"
+
     # available ray device keys:
     # https://github.com/ray-project/ray/blob/10ba5adadcc49c60af2c358a33bb943fb491a171/python/ray/_private/ray_constants.py#L438 # noqa
     # empty string means the device does not support ray
     ray_device_key: str = ""
+
+    # platform-agnostic way to specify the device control environment variable,
+    # .e.g. CUDA_VISIBLE_DEVICES for CUDA.
+    # hint: search for "get_visible_accelerator_ids_env_var" in
+    # https://github.com/ray-project/ray/tree/master/python/ray/_private/accelerators # noqa
+    device_control_env_var: str = "VLLM_DEVICE_CONTROL_ENV_VAR_PLACEHOLDER"
+
     # The torch.compile backend for compiling simple and
     # standalone functions. The default value is "inductor" to keep
     # the same behavior as PyTorch.
     # NOTE: for the forward part of the model, vLLM has another separate
     # compilation strategy.
     simple_compile_backend: str = "inductor"
+
     supported_quantization: list[str] = []
 
     def is_cuda(self) -> bool: