Both NIC and transport drivers allocate and manage virtual memory buffers in the host. The NDIS interface library provides functions that allow the drivers to allocate, construct, and inspect such buffers. These buffers are listed in Table A.2.6.
NDIS 3.0 (ndis.h) uses an NDIS_BUFFER structure to define a variable-length buffer descriptor for a buffer. A buffer descriptor is an MDL that contains virtual and physical addressing information for the buffer, the buffer length, and a pointer to the next buffer descriptor in the chain of buffer descriptors that make up a packet descriptor.
For bus-mastering transfers, a NIC driver needs to send the physical addresses of virtual memory buffers to its network interface card. Under NDIS 3.0, the driver can obtain these addresses by calling NdisStartBufferPhysicalMapping. A portable NIC driver has limited use of physical addresses and sometimes only has knowledge of a virtual address when the network interface card requires a physical address. The operating system must then map the virtual address to an appropriate physical address. The resultant mapping is temporary and the NIC driver must manage it using map registers.
Table A.2.6 Buffer Functions
| Function | Definition |
| NdisAdjustBufferLength | Modifies the length field in an allocated buffer descriptor. |
| NdisAllocateBuffer | Allocates and initializes a buffer descriptor for virtual memory. |
| NdisAllocateBufferPool | Allocates and initializes a block of storage for a pool of buffer descriptors. |
| NDIS_BUFFER_LINKAGE | Retrieves the internal buffer linkage from a buffer descriptor for use by a transport driver. |
| NdisChainBufferAtBack | Appends a buffer descriptor to a chain of buffer descriptors for a packet descriptor. |
| NdisChainBufferAtFront | Adds a buffer descriptor at the front of a chain of buffer descriptors for a packet descriptor. |
| NdisCompleteBufferPhysicalMapping | Indicates to the operating system that a physical address mapping is no longer needed. |
| NdisCopyBuffer | Creates a buffer descriptor for a specific memory descriptor that a higher network layer passes to the transport driver. |
| NdisCreateLookaheadBufferFrom SharedMemory | Provides a lookahead buffer, which is a virtual memory copy of shared memory on the network interface card. |
| NdisDestroyLookaheadBufferFrom SharedMemory | Disassociates a lookahead buffer from shared memory on the network card. |
| NdisFreeBuffer | Frees a buffer descriptor. |
| NdisFreeBufferPool | Terminates the use of a buffer descriptor pool. |
| NdisGetBufferPhysicalAddress | Obtains the physical segments that make up a single buffer. This function is obsolete, and NdisStartBufferPhysicalMapping replaces it. |
| NdisGetBufferPhysicalArraySize | Determines the maximum number of physical segments in a buffer. |
| NdisGetNextBuffer | Finds the next buffer descriptor in a buffer descriptor chain. |
| NdisGetPhysicalAddressHigh | Queries the high 32 bits of a physical address. |
| NdisGetPhysicalAddressLow | Returns the low 32 bits of a physical address. |
| NdisQueryBuffer | Queries a specified buffer descriptor. |
| NdisSetPhysicalAddressHigh | Sets the high 32 bits of a physical address. |
| NdisSetPhysicalAddressLow | Sets the low 32 bits of a physical address. |
| NdisStartBufferPhysicalMapping | Starts a mapping that the NDIS interface library uses to associate the virtual address of a buffer with the addresses of its physical segments. Replaces function NdisGetBufferPhysicalAddress that is no longer supported. |
| NdisUnchainBufferAtBack | Removes the last buffer descriptor from a buffer descriptor chain. |
| NdisUnchainBufferAtFront | Removes the first buffer descriptor from a buffer descriptor chain. |