FsRtlLookupLargeMcbEntry function (ntifs.h)

Article
09/27/2023

Given a virtual block number (VBN) and a map control block (MCB), the FsRtlLookupLargeMcbEntry routine searches the MCB for mapping information corresponding to the specified VBN.

Syntax

BOOLEAN FsRtlLookupLargeMcbEntry(
                  PLARGE_MCB Mcb,
                  LONGLONG   Vbn,
                  PLONGLONG  Lbn,
                  PLONGLONG  SectorCountFromLbn,
                  PLONGLONG  StartingLbn,
                  PLONGLONG  SectorCountFromStartingLbn,
  [out, optional] PULONG     Index
);

Parameters

Mcb

Pointer to an initialized MCB structure.

Vbn

Pointer to the requested VBN.

Lbn

Pointer to a variable that receives the LBN that is mapped to LargeVbn in the mapping entry, or -1 if no such LBN exists. This parameter is optional and can be NULL.

SectorCountFromLbn

Pointer to a variable that receives the number of sectors that follow LargeVbn in the mapping run. This parameter is optional and can be NULL.

StartingLbn

Pointer to a variable that receives the LBN corresponding to the start of the mapping run, or -1 if no such LBN exists. This parameter is optional and can be NULL.

SectorCountFromStartingLbn

Pointer to a variable that receives the number of sectors in the mapping run. This parameter is optional and can be NULL.

[out, optional] Index

Pointer to a variable that receives the index of the mapping run that contains the VBN. This parameter is optional and can be NULL.

Return value

FsRtlLookupLargeMcbEntry returns TRUE if the specified VBN is within the range of VBNs that are mapped by the MCB, FALSE otherwise.

Remarks

FsRtlLookupLargeMcbEntry searches for a mapping entry in the MCB whose run includes the specified VBN.

If such a mapping exists, the lookup operation yields positive values for the corresponding LBN and sector count, and FsRtlLookupLargeMcbEntry returns TRUE.
If no such mapping exists, but the specified VBN is lower than the highest VBN mapped by the MCB, this is referred to as a hole in the mapping. In this case, FsRtlLookupLargeMcbEntry still returns TRUE, but the lookup operation yields a value of -1 for the LBN.
If the specified VBN is higher than the highest VBN mapped by the MCB, or if the MCB contains no mappings, FsRtlLookupLargeMcbEntry returns FALSE.

The upper 32 bits of the LBN are ignored. Only the lower 32 bits are used.

Requirements

Requirement	Value
Target Platform	Universal
Header	ntifs.h (include Ntifs.h)
Library	NtosKrnl.lib
DLL	NtosKrnl.exe
IRQL	<= APC_LEVEL