NdisSend

This function forwards a send request to the underlying driver.

At a Glance

Syntax

VOID NdisSend( OUT PNDIS_STATUS Status,
IN NDIS_HANDLE NdisBindingHandle, IN PNDIS_PACKET Packet );

Parameters

Status

Pointer to a caller-supplied variable that is set on return from this function. The underlying driver determines which NDIS_STATUS_XXX is returned, but it is usually one of the following values:

NDIS_STATUS_SUCCESS

The specified packet is being transmitted over the network.

NDIS_STATUS_PENDING

The request is being handled asynchronously, and the caller’s ProtocolSendComplete function will be called when it is completed.

NDIS_STATUS_INVALID_PACKET

The size of the requested transfer is too large for the NIC, or possibly the NIC indicated an erroneous packet transmission to its driver.

NDIS_STATUS_CLOSING

The underlying driver is closing.

NDIS_STATUS_RESET_IN_PROGRESS

The underlying driver is currently resetting the NIC. The caller’s ProtocolStatus function was or will be called with NDIS_STATUS_RESET_START to indicate that a reset is in progress.

NDIS_STATUS_FAILURE

This value is usually a nonspecific default returned when none of the more specific NDIS_STATUS_XXX caused the underlying driver to fail the request.

The specific NDIS_STATUS_XXX returned for device I/O errors that occur during a transmit operation depends on the nature of the NIC and the discretion of the NIC driver writer. For example, a miniport might return NDIS_STATUS_NO_CABLE if its NIC indicates this condition to the driver.

NdisBindingHandle

Handle returned by the NdisOpenAdapter function that identifies the target NIC or the virtual adapter of the next-lower driver to which the caller is bound.

Packet

Pointer to the caller-supplied packet descriptor, allocated with the NdisAllocatePacket function, with chained buffer descriptors mapping buffers containing the data that the underlying NIC driver should transmit over the wire.

Remarks

Before calling this function, a protocol driver can call the NdisSetPacketFlags function to set the flags in the private header, reserved for use by NDIS, of the packet descriptor that it allocated. These flags specify caller-determined information about the requested send operation that is not contained in the packet data. The underlying NIC driver’s MiniportSend function is given the send flags as an input parameter. The meaning of the packet flags bits is medium-specific and defined by the pair of collaborating drivers.

However, such a pair of collaborating drivers can use the NDIS_PACKET_OOB_DATA structure associated with each packet descriptor to communicate far more information than the packet flags can convey. Before calling this function, a protocol can use the NDIS_SET_PACKET_TIME_TO_SEND and/or NDIS_SET_PACKET_MEDIA_SPECIFIC_INFO macros to set up out-of-band information, if any, relevant to the underlying driver in the NDIS_PACKET_OOB_DATA structure associated with the protocol-allocated packet descriptor.

When an underlying driver has insufficient resources to transmit a valid send packet, the driver has two alternatives:

• Its MiniportSend function can insert the packet into an internal queue and return NDIS_STATUS_PENDING.

  The driver holds the packet queued until resources become available and sends the packet when they are.

• Its MiniportSend function can return control with NDIS_STATUS_RESOURCES.

  The NDIS library holds such a returned packet in an internal queue for resubmission to the miniport. The miniport indicates its readiness to accept send packets later by calling NdisMSendResourcesAvailable or NdisMSendComplete, whichever call occurs first.

In either of the preceding situations, this function returns NDIS_STATUS_PENDING to the caller, and the driver’s ProtocolSendComplete function is called when the packet is transmitted.

As soon as a protocol calls this function, it relinquishes ownership of the packet descriptor at Packet of all buffers mapped by buffer descriptors that it chained to the packet and of any out-of-band information that it supplied with the packet descriptor. The protocol regains ownership of these resources when the packet is completed with a status other than NDIS_STATUS_PENDING or when its ProtocolSendComplete function is called.

When either occurs, the protocol can call the NdisReinitializePacket function to prepare the packet for reuse after saving the buffer descriptors chained to the packet descriptor with calls to an NdisUnchainBufferAtXXX function. Reusing such a packet descriptor yields better performance than returning the packet to driver-allocated packet pool with the NdisFreePacket function, and then reallocating it for another send later.

An NDIS intermediate driver must repackage incoming sends from still higher level protocols in fresh packet descriptors before passing such a send request to the underlying miniport with this function.

A driver that calls this function runs at IRQL <= DISPATCH_LEVEL.

See Also

NdisAllocateBuffer, NdisAllocatePacket, NdisFreePacket, NdisGetPacketFlags, NdisMSendResourcesAvailable, NdisReinitializePacket, NdisUnchainBufferAtBack, NdisUnchainBufferAtFront