FltEnumerateFilterInformation function (fltkernel.h)

Article
10/21/2021

The FltEnumerateFilterInformation routine provides information about all the registered filter drivers (including minifilter and legacy filter drivers) in the system.

Syntax

NTSTATUS FLTAPI FltEnumerateFilterInformation(
  [in]  ULONG                    Index,
  [in]  FILTER_INFORMATION_CLASS InformationClass,
  [out] PVOID                    Buffer,
  [in]  ULONG                    BufferSize,
  [out] PULONG                   BytesReturned
);

Parameters

[in] Index

Zero-based index of the filter driver for which the information is requested. This parameter identifies the filter in the global list of registered filter drivers. If the list contains n filter drivers, valid Index values range from 0 to n-1. If the Index value exceeds this range, FltEnumerateFilterInformation returns STATUS_NO_MORE_ENTRIES.

[in] InformationClass

Type of information requested. This parameter can have one of the following values.

Value	Meaning
FilterFullInformation	The buffer pointed to by the Buffer parameter receives a FILTER_FULL_INFORMATION structure for the minifilter driver (legacy filter drivers are ignored).
FilterAggregateBasicInformation	The buffer pointed to by the Buffer parameter receives a FILTER_AGGREGATE_BASIC_INFORMATION structure for the minifilter or legacy filter driver. This InformationClass value is available starting with Microsoft Windows Server 2003 SP1 and Windows XP SP2 with filter manager rollup. For more about the filter manager rollup package for Windows XP SP2, see article 914882, "The filter manager rollup package for Windows XP SP2," in the Microsoft Knowledge Base.
FilterAggregateStandardInformation	The buffer pointed to by the Buffer parameter receives a FILTER_AGGREGATE_STANDARD_INFORMATION structure for the minifilter or legacy filter driver. This InformationClass value is available starting with Windows Vista.

[out] Buffer

Pointer to a caller-allocated buffer that receives the requested information. The type of the information returned in the buffer is defined by the InformationClass parameter.

[in] BufferSize

Size, in bytes, of the buffer that the Buffer parameter points to. The caller should set this parameter according to the given InformationClass value.

[out] BytesReturned

Pointer to a caller-allocated variable that receives the number of bytes returned in the buffer that Buffer points to. If the input value of BufferSize is too small, FltEnumerateFilterInformation returns STATUS_BUFFER_TOO_SMALL and sets this variable to the number of bytes required to store the requested information. This parameter is required and cannot be NULL.

Return value

FltEnumerateFilterInformation returns STATUS_SUCCESS or an appropriate NTSTATUS value, such as one of the following:

Return code	Description
STATUS_BUFFER_TOO_SMALL	The buffer that the Buffer parameter points to is not large enough to store the requested information. This is an error code.
STATUS_FLT_DELETING_OBJECT	A matching minifilter driver was found, but it is being torn down. This is an error code.
STATUS_INVALID_PARAMETER	An invalid value was specified for the InformationClass parameter. For example, if FilterAggregateStandardInformation is specified on operating systems prior to Windows Vista, the routine will return STATUS_INVALID_PARAMETER. This is an error code.
STATUS_NO_MORE_ENTRIES	There are no more entries in the global list of registered filter drivers. (The value of the Index parameter is greater than or equal to the number of filter drivers.) This is a warning code.

Remarks

Starting with Microsoft Windows Server 2003 SP1 and Windows XP SP2 with filter manager rollup, FltEnumerateFilterInformation provides information about file system filter drivers (also called "legacy filters") as well as minifilter drivers. On earlier versions of Windows, FltEnumerateFilterInformation only provides information about minifilter drivers.

The following pseudocode enumerates filter information for all registered filter drivers.

#define InfoClass FilterAggregateStandardInformation   // Assumes Windows Vista or later operating system.

int i = 0;
while ( FltEnumerateFilterInformation(i, InfoClass, ...) != STATUS_NO_MORE_ENTRIES )
{
 Process acquired filter driver information returned by the Buffer parameter of FltEnumerateFilterInformation, if applicable.
 i++;
}

FltEnumerateFilterInformation returns information about registered filter drivers, through the Buffer parameter, in order of decreasing distance from the underlying file system. For example, assume that there are n filter drivers attached above an underlying file system. Information about the filter driver attached farthest from the file system is returned first (with an Index parameter value of 0). Information about the next-farthest attached filter driver is returned second (with an Index parameter value of 1), and so on. Finally, information about the filter driver closest to the file system is returned last (with an Index parameter value of n-1).

Note Because filter drivers can register at any time, it is possible that two calls to FltEnumerateFilterInformation with the same Index might not return the same result.

To enumerate all registered minifilter drivers, call FltEnumerateFilters.

To enumerate all registered legacy filter drivers, call IoEnumerateRegisteredFiltersList.

To enumerate all instances of a given minifilter driver, call FltEnumerateInstanceInformationByFilter.

To enumerate all minifilter driver instances on a given volume, call FltEnumerateInstanceInformationByVolume.

To list volume information for all volumes that are known to the Filter Manager, call FltEnumerateVolumeInformation.

Requirements

Requirement	Value
Target Platform	Universal
Header	fltkernel.h (include FltKernel.h)
Library	FltMgr.lib
IRQL	<= APC_LEVEL