chore: import upstream snapshot with attribution

vllm/model_executor/layers/attention_layer_base.py

@@ -0,0 +1,35 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+"""Base class for attention-like layers."""
+
+from abc import ABC, abstractmethod
+
+from vllm.config import VllmConfig
+from vllm.v1.attention.backend import AttentionBackend, AttentionImpl
+from vllm.v1.kv_cache_interface import KVCacheSpec
+
+
+class AttentionLayerBase(ABC):
+    """
+    Base class for attention-like layers (Attention, Mamba, etc.)
+    that support the v1 engine.
+
+    This provides a common interface for getting attention backends
+    from different layer types.
+    """
+
+    impl: "AttentionImpl"
+    supports_dcp: bool = True
+
+    @abstractmethod
+    def get_attn_backend(self) -> type[AttentionBackend]:
+        """Get the attention backend class for this layer."""
+        pass
+
+    @abstractmethod
+    def get_kv_cache_spec(self, vllm_config: VllmConfig) -> KVCacheSpec | None:
+        """
+        Get the KV cache spec for this layer.
+        May be None if the layer does not need KV cache.
+        """
+        pass