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OID_TCP_TASK_OFFLOAD

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The host stack queries the OID_TCP_TASK_OFFLOAD OID to obtain the TCP offload capabilities of a miniport driver's NIC or of an offload target. After determining the offload capabilities that a NIC or an offload target supports, the host stack sets this OID to enable one or more of the reported capabilities. The host stack can also disable all of a NIC's or an offload target's TCP offload capabilities by setting OID_TCP_TASK_OFFLOAD. Only one protocol at a time can enable the TCP offload capabilities of a particular NIC.

Querying offload capabilities

When the host stack queries OID_TCP_TASK_OFFLOAD, it supplies in the InformationBuffer an NDIS_TASK_OFFLOAD_HEADER structure. This structure specifies the following:

  • The offload version supported by the host stack.
  • The encapsulation format for send and receive packets processed by the host stack.
  • The size of the encapsulation header in such packets.

With this information, a miniport driver or its NIC can locate the beginning of the first IP header in a transmit packet, which is a prerequisite for performing an offload task. An offload target needs to know the encapsulation format to process receive packets. In response to a query of OID_TCP_TASK_OFFLOAD, a miniport driver or offload target returns, in the InformationBuffer, the NDIS_TASK_OFFLOAD_HEADER structure followed immediately by one or more NDIS_TASK_OFFLOAD structures. Each NDIS_TASK_OFFLOAD structure describes an offload capability supported by the miniport driver's NIC or by the offload target. If the miniport driver's NIC or the offload target supports multiple versions of a particular offload capability, it should return one NDIS_TASK_OFFLOAD structure for each version.

Each NDIS_TASK_OFFLOAD structure has a Task member that specifies the particular offload capability to which the structure applies. Each NDIS_TASK_OFFLOAD structure also has a TaskBuffer that contains information pertinent to the specified offload capability. The information in the TaskBuffer is formatted as one of the following structures:

Note

If an intermediate driver modifies the contents of packets that it forwards to an underlying miniport driver such that TCP offload functions cannot be performed on the packets, the intermediate driver should respond to OID_TCP_TASK_OFFLOAD queries with a status of NDIS_STATUS_NOT_SUPPORTED instead of passing the OID request to the underlying miniport driver or offload target.

Enabling offload capabilities

After querying a NIC's or an offload target's offload capabilities, the host stack enables one or more of these capabilities by setting OID_TCP_TASK_OFFLOAD. When setting OID_TCP_TASK_OFFLOAD, the host stack supplies, in the InformationBuffer, an NDIS_TASK_OFFLOAD_HEADER structure followed immediately by an NDIS_TASK_OFFLOAD structure for each offload capability that the host stack is enabling.

The Task in each NDIS_TASK_OFFLOAD structure indicates the offload capability that the host stack is enabling. The host stack also enables specific aspects of a particular offload capability by setting members of the structure in the TaskBuffer of each NDIS_TASK_OFFLOAD structure.

Changing offload capabilities

To change the offload capabilities that are enabled for a NIC or an offload target, the host stack sets OID_TCP_TASK_OFFLOAD. The miniport driver or offload target must enable only those offload capabilities specified by the most recent set of OID_TCP_TASK_OFFLOAD. The miniport driver or offload target must disable all other offload capabilities. Note that before disabling a specific TCP chimney offload capability, the host stack terminates the offload of any offloaded TCP connections that use that capability.

An offload target can use pause or resume offload indications to change its reported TCP offload capabilities:

  • An offload target makes a pause indication by calling the NdisMIndicateStatusEx function with the NDIS_STATUS_INDICATION->StatusCode member set to NDIS_STATUS_OFFLOAD_PAUSE.
  • An offload target makes a resume indication by calling the NdisMIndicateStatusEx function with the NDIS_STATUS_INDICATION->StatusCode member set to NDIS_STATUS_OFFLOAD_RESUME.

After an offload target requests the host stack to resume offloading state objects, the host stack queries OID_TCP_TASK_OFFLOAD again to obtain the offload target's TCP offload revised capabilities. For more information, see NDIS_STATUS_OFFLOAD_RESUME.

Disabling offload capabilities

To disable all offload capabilities supported by a NIC or an offload target, the host stack sets OID_TCP_TASK_OFFLOAD. In the InformationBuffer, the host stack supplies an NDIS_TASK_OFFLOAD_HEADER structure with the OffsetFirstTask member of this structure set to zero.

Requirements

Version: Windows Vista and later Header: Ntddndis.h (include Ndis.h)