FltGetLowerInstance function (fltkernel.h)

The FltGetLowerInstance routine returns an opaque instance pointer for the next lower minifilter driver instance, if there is one, that is attached below a given minifilter driver instance on the same volume.

Syntax

NTSTATUS FLTAPI FltGetLowerInstance(
  [in]  PFLT_INSTANCE CurrentInstance,
  [out] PFLT_INSTANCE *LowerInstance
);

Parameters

[in] CurrentInstance

Opaque instance pointer for the minifilter driver instance for which the lower minifilter driver instance is requested.

[out] LowerInstance

Pointer to a caller-allocated variable that receives an opaque minifilter driver instance pointer for the next lower minifilter driver instance. This parameter is required and cannot be NULL.

Return value

FltGetLowerInstance returns STATUS_SUCCESS or an appropriate NTSTATUS value, such as the following:

Remarks

One instance is said to be below another if it is attached at a lower altitude on the same volume. The term "altitude" refers to the position that an instance occupies (or should occupy) in the minifilter driver instance stack for a volume. The higher the altitude, the farther the instance is from the base file system in the stack. Only one instance can be attached at a given altitude on a given volume.

Altitude is specified by an altitude string, which is a counted Unicode string consisting of one or more decimal digits from 0 through 9, and it can include a single decimal point. For example, "100.123456" and "03333" are valid altitude strings.

The string "03333" represents a higher altitude than "100.123456". (Leading and trailing zeros are ignored.) In other words, an instance whose altitude is "03333" is farther from the base file system than an instance whose altitude is "100.123456". However, this comparison is only meaningful if both instances are attached to the same volume.

FltGetLowerInstance adds a rundown reference to the opaque instance pointer returned in the LowerInstance parameter. When this pointer is no longer needed, the caller must release it by calling FltObjectDereference. Thus every successful call to FltGetLowerInstance must be matched by a subsequent call to FltObjectDereference.

Requirements

See also

FltAttachVolume

FltAttachVolumeAtAltitude

FltCompareInstanceAltitudes

FltGetBottomInstance

FltGetTopInstance

FltGetUpperInstance

FltObjectDereference