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WofIsExternalFile function (wofapi.h)

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Used to determine if a file is being backed by a physical file or is backed by a system data provider, and optionally indicates which provider or additional data about the file.

Syntax

HRESULT WofIsExternalFile(
  [in]                LPCWSTR FilePath,
  [out, optional]     PBOOL   IsExternalFile,
  [out, optional]     PULONG  Provider,
  [out, optional]     PVOID   ExternalFileInfo,
  [in, out, optional] PULONG  BufferLength
);

Parameters

[in] FilePath

Specifies the path to the file for which the backing state is desired.

[out, optional] IsExternalFile

Optionally points to a BOOL value. On successful return, this value will be TRUE if the object is externally backed, FALSE if it is a physical file.

[out, optional] Provider

Optionally points to a ULONG value. On successful return, this value will be set to the provider that externally backs this object. Currently defined providers are:

WOF_PROVIDER_WIM Indicates that the data for the file resides in a separate WIM file. On access, data is transparently extracted, decompressed and provided to applications. If the file contents are modified, data is transparently decompressed and the file is restored to a regular file.
WOF_PROVIDER_FILE Indicates that the data for the file should be compressed and stored with the file itself. On access, data is transparently decompressed and provided to applications. If the file contents are modified, data is transparently decompressed and the file is restored to a regular file. This provider requires Windows 10.

[out, optional] ExternalFileInfo

Optionally points to a caller allocated buffer. On successful return, this buffer will contain additional information about the state of the file. If this value is provided, BufferLength must also be specified. Data structures for each defined provider are:

WOF_PROVIDER_WIM WIM_EXTERNAL_FILE_INFO
WOF_PROVIDER_FILE WOF_FILE_COMPRESSION_INFO

[in, out, optional] BufferLength

Optionally points to a value that contains the length of the buffer specified in ExternalFileInfo. On return, this value will be set to the size of the buffer consumed, or the size of the buffer required. If the buffer is of insufficient length, this function will succeed indicating the required size and will not populate the buffer in ExternalFileInfo. This length should correspond to one of the structures defined above:

WOF_PROVIDER_WIM sizeof(WIM_EXTERNAL_FILE_INFO)
WOF_PROVIDER_FILE sizeof(WOF_FILE_COMPRESSION_INFO)

Return value

This function returns an HRESULT indicating success or the reason for failure. If the buffer specified in ExternalFileInfo is not of the correct size, the function will return S_OK and indicate the required buffer size in BufferLength.

Requirements

Requirement Value
Target Platform Windows
Header wofapi.h
Library Wofutil.lib
DLL Wofutil.dll

See also

FSCTL_GET_EXTERNAL_BACKING