NdisFreeMemory (NDIS 5.1) function

Article
06/19/2017

Note NDIS 5. x has been deprecated and is superseded by NDIS 6. x. For new NDIS driver development, see Network Drivers Starting with Windows Vista. For information about porting NDIS 5. x drivers to NDIS 6. x, see Porting NDIS 5.x Drivers to NDIS 6.0.

NdisFreeMemory releases a block of memory previously allocated with NdisAllocateMemory or NdisAllocateMemoryWithTag.

Syntax

VOID NdisFreeMemory(
  _In_ PVOID VirtualAddress,
  _In_ UINT  Length,
  _In_ UINT  MemoryFlags
);

Parameters

VirtualAddress [in]
Pointer to the base virtual address of the allocated memory. This address was returned by NdisAllocateMemory or NdisAllocateMemoryWithTag.
Length [in]
Specifies the size in bytes of the memory block to be released. This parameter must be identical to the Length that was passed to NdisAllocateMemory. However, if the memory was allocated with NdisAllocateMemoryWithTag or the MemoryFlags parameter is zero, this parameter is ignored.
MemoryFlags [in]
Specifies zero or the bitmask originally passed to NdisAllocateMemory for the preceding range, designating the following:

Value Meaning

zero

Nonpaged system-space memory

NDIS_MEMORY_CONTIGUOUS

Physically contiguous memory

NDIS_MEMORY_NONCACHED

Noncached memory

This value must be zero if the memory was allocated with NdisAllocateMemoryWithTag. This value must be identical to the MemoryFlags that was passed to NdisAllocateMemory.

Value	Meaning
zero	Nonpaged system-space memory
NDIS_MEMORY_CONTIGUOUS	Physically contiguous memory
NDIS_MEMORY_NONCACHED	Noncached memory

Return value

None

Remarks

The parameters passed to NdisFreeMemory must be identical to those passed to NdisAllocateMemory when the block of memory was allocated. That is, a caller of NdisFreeMemory cannot release a subrange of the block that was allocated.

Because noncached memory and contiguous memory are seldom released until the allocating NIC driver is unloading, a caller of NdisFreeMemory usually is running at IRQL = PASSIVE_LEVEL for these types of deallocations. In any case:

When releasing contiguous memory, a caller of NdisFreeMemory must be running at IRQL = PASSIVE_LEVEL
When releasing noncached memory, a caller of NdisFreeMemory must be running at IRQL < DISPATCH_LEVEL
When releasing memory that is neither contiguous nor noncached, a caller of NdisFreeMemory must be running at IRQL <= DISPATCH_LEVEL

Requirements

Target platform	Universal
Version	See NdisFreeMemory.
Header	Ndis.h (include Ndis.h)
Library	Ndis.lib
IRQL	See Remarks section.

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