describe what if topology not match exactly

Describe what to expect when the accessible_topology of node and volume does
not match exactly.

csi.proto

@@ -579,6 +579,11 @@ message Volume {
   // COs MAY use this information along with the topology information
   // returned by NodeGetInfo to ensure that a given volume is accessible
   // from a given node when scheduling workloads.
+  // The volume is accessible from all locations in the
+  // specified topology.
+  // The volume is accessible from a node if the volume's
+  // accessible_topology is a superset of the node's
+  // accessible_topology.
   // This field is OPTIONAL. If it is not specified, the CO MAY assume
   // the volume is equally accessible from all nodes in the cluster and
   // MAY schedule workloads referencing the volume on any available
@@ -1677,6 +1682,10 @@ message NodeGetInfoResponse {
   // COs MAY use this information along with the topology information
   // returned in CreateVolumeResponse to ensure that a given volume is
   // accessible from a given node when scheduling workloads.
+  // The node can access some of the locations in the
+  // specified topology.
+  // The node can access a volume if the node's accessible_topology
+  // is a subset of the volume's accessible_topology.
   // This field is OPTIONAL. If it is not specified, the CO MAY assume
   // the node is not subject to any topological constraint, and MAY
   // schedule workloads that reference any volume V, such that there are
@@ -1686,7 +1695,12 @@ message NodeGetInfoResponse {
   //   accessible_topology =
   //     {"region": "R1", "zone": "Z2"}
   // Indicates the node exists within the "region" "R1" and the "zone"
-  // "Z2".
+  // "Z2". And it can access the following volumes:
+  //   Volume 1: accessible_topology = {"region": "R1", "zone": "Z2"}
+  //   Volume 2: accessible_topology = {"region": "R1"}
+  // But can not access the following volume:
+  //   Volume 3: accessible_topology =
+  //     {"region": "R1", "zone": "Z2", "rack": "R3"}
   Topology accessible_topology = 3;
 }
 message NodeExpandVolumeRequest {

spec.md

@@ -1050,6 +1050,11 @@ message Volume {
   // COs MAY use this information along with the topology information
   // returned by NodeGetInfo to ensure that a given volume is accessible
   // from a given node when scheduling workloads.
+  // The volume is accessible from all locations in the
+  // specified topology.
+  // The volume is accessible from a node if the volume's
+  // accessible_topology is a superset of the node's
+  // accessible_topology.
   // This field is OPTIONAL. If it is not specified, the CO MAY assume
   // the volume is equally accessible from all nodes in the cluster and
   // MAY schedule workloads referencing the volume on any available
@@ -2767,6 +2772,10 @@ message NodeGetInfoResponse {
   // COs MAY use this information along with the topology information
   // returned in CreateVolumeResponse to ensure that a given volume is
   // accessible from a given node when scheduling workloads.
+  // The node can access some of the locations in the
+  // specified topology.
+  // The node can access a volume if the node's accessible_topology
+  // is a subset of the volume's accessible_topology.
   // This field is OPTIONAL. If it is not specified, the CO MAY assume
   // the node is not subject to any topological constraint, and MAY
   // schedule workloads that reference any volume V, such that there are
@@ -2776,7 +2785,12 @@ message NodeGetInfoResponse {
   //   accessible_topology =
   //     {"region": "R1", "zone": "Z2"}
   // Indicates the node exists within the "region" "R1" and the "zone"
-  // "Z2".
+  // "Z2". And it can access the following volumes:
+  //   Volume 1: accessible_topology = {"region": "R1", "zone": "Z2"}
+  //   Volume 2: accessible_topology = {"region": "R1"}
+  // But can not access the following volume:
+  //   Volume 3: accessible_topology =
+  //     {"region": "R1", "zone": "Z2", "rack": "R3"}
   Topology accessible_topology = 3;
 }
 ```