RtlInitializeBitMap function (wdm.h)

Article
02/22/2024

The RtlInitializeBitMap routine initializes the header of a bitmap variable.

Syntax

NTSYSAPI VOID RtlInitializeBitMap(
  [out] PRTL_BITMAP             BitMapHeader,
  [in]  __drv_aliasesMem PULONG BitMapBuffer,
  [in]  ULONG                   SizeOfBitMap
);

Parameters

[out] BitMapHeader

Pointer to an empty RTL_BITMAP structure.

[in] BitMapBuffer

Pointer to caller-allocated memory for the bitmap itself. The base address of this buffer must be ULONG-aligned. The size of the allocated buffer must be an integer multiple of sizeof(ULONG) bytes.

[in] SizeOfBitMap

Specifies the number of bits in the bitmap. This value can be any number of bits that will fit in the buffer allocated for the bitmap.

Return value

None

Remarks

A driver can use a bitmap variable as an economical way to keep track of a set of reusable items. For example, file systems use a bitmap variable to track which clusters/sectors on a disk have already been allocated to hold file data. The system-supplied SCSI port driver uses a bitmap variable to track which queue tags have been assigned to SCSI request blocks (SRBs).

RtlInitializeBitMap must be called before any other RtlXxx routine that operates on a bitmap variable. The BitMapHeader pointer is an input parameter in all subsequent RtlXxx calls that operate on the caller's bitmap variable at BitMapBuffer. The caller is responsible for synchronizing access to the bitmap variable.

RtlInitializeBitMap initializes the caller-supplied RTL_BITMAP structure by copying the caller-supplied BitMapBuffer and SizeOfBitMap values into it. Subsequently, the structure can be passed to other routines to manipulate the bitmap. RtlInitializeBitMap does not modify the contents of the bitmap.

Requirements

Requirement	Value
Minimum supported client	Available starting with Windows 2000.
Target Platform	Universal
Header	wdm.h (include Wdm.h, Ntddk.h, Ntifs.h)
Library	NtosKrnl.lib
DLL	NtosKrnl.exe (kernel mode); Ntdll.dll (user mode)
IRQL	Any IRQL if BitMapHeader is memory-resident; <= APC_LEVEL if BitMapHeader is pageable or on Windows 7 and earlier