FsRtlLookupBaseMcbEntry function (ntifs.h)

The FsRtlLookupBaseMcbEntry routine retrieves the mapping of a virtual block number (VBN) to a logical block number (LBN) from a map control block (MCB). It indicates if the mapping exists and the size of the run.

Syntax

BOOLEAN FsRtlLookupBaseMcbEntry(
  PBASE_MCB Mcb,
  LONGLONG  Vbn,
  PLONGLONG Lbn,
  PLONGLONG SectorCountFromLbn,
  PLONGLONG StartingLbn,
  PLONGLONG SectorCountFromStartingLbn,
  PULONG    Index
);

Parameters

Mcb

Supplies the Mcb being examined.

Vbn

Supplies the Vbn to lookup.

Lbn

Receives the Lbn corresponding to the Vbn. A value of -1 is returned if the Vbn does not have a corresponding Lbn.

SectorCountFromLbn

Receives the number of sectors that map from the Vbn to contiguous Lbn values beginning with the input Vbn.

StartingLbn

Contains the lbn at the start of the run. If it's a hole then the starting Lbn is zero.

SectorCountFromStartingLbn

Contains the number of sectors at the start of the run if a sector count argument is present.

Index

Receives the index of the run found.

Return value

This function returns TRUE if the Vbn is within the range of VBNs mapped by the MCB (even if it corresponds to a hole in the mapping), and FALSE if the Vbn is beyond the range of the MCB's mapping.

For example, if an MCB has a mapping for VBNs 5 and 7 but not for 6, then a lookup on Vbn 5 or 7 will yield a non zero Lbn and a sector count of 1. A lookup for Vbn 6 will return TRUE with an Lbn value of 0, and lookup for Vbn 8 or above will return FALSE.

Requirements

Requirement	Value
Header	ntifs.h