FsRtlNumberOfRunsInLargeMcb function (ntifs.h)

Article
04/01/2021

The FsRtlNumberOfRunsInLargeMcb routine returns the number of runs in a map control block (MCB).

Syntax

ULONG FsRtlNumberOfRunsInLargeMcb(
  PLARGE_MCB Mcb
);

Parameters

Mcb

Supplies the MCB being examined.

Return value

Returns the number of distinct runs mapped by the input MCB.

Remarks

FsRtlNumberOfRunsInLargeMcb returns the number of distinct runs mapped by an MCB.

Runs can be mappings or holes. A mapping is a continuous range of VBNs that is mapped to a corresponding range of logical block numbers (LBN). Mappings cannot overlap. A hole is a continuous range of unmapped VBNs that falls between two mappings. Within the entire range of mapped VBNs, every VBN belongs to exactly one mapping or hole.

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

FsRtlNumberOfRunsInLargeMcb counts both types of runs. For example, an MCB containing a mapping for only VBNs zero and three will have three runs: one for VBN 0, one for the hole covering VBN 1 and VBN 2, and one for VBN 3.

Requirements

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