IVssComponent::GetPartialFile method (vswriter.h)

Article
10/13/2021

The GetPartialFile method returns information on a partial file associated with this component.

Syntax

HRESULT GetPartialFile(
  [in]  UINT iPartialFile,
  [out] BSTR *pbstrPath,
  [out] BSTR *pbstrFilename,
  [out] BSTR *pbstrRange,
  [out] BSTR *pbstrMetadata
);

Parameters

[in] iPartialFile

Index number of the partial file. The value of this parameter is an integer from 0 to n–1 inclusive, where n is the total number of partial files associated with a given component. The value of n is returned by IVssComponent::GetPartialFileCount.

[out] pbstrPath

Pointer to a string containing the path of the partial file.

Users of this method need to check to determine whether this path ends with a backslash ("").

[out] pbstrFilename

Pointer to a string containing the name of the partial file.

[out] pbstrRange

A pointer to a string containing either a listing of file offsets and lengths that make up the partial file support range (the sections of the file that were backed up), or the name of a file containing such a list.

[out] pbstrMetadata

Pointer to a string containing any additional metadata required by a writer to validate a partial file restore operation. The information in this metadata string will be opaque to requesters.

Additional metadata is not required, so pbstrMetadata may also be empty (zero length).

Return value

The following are the valid return codes for this method.

Value	Meaning
S_OK	Successfully returned the attribute value.
E_INVALIDARG	One of the parameter values is not valid.
E_OUTOFMEMORY	The caller is out of memory or other system resources.
VSS_E_BAD_STATE	The caller is not in the correct state (either backup or restore) for the operation.
VSS_E_INVALID_XML_DOCUMENT	The XML document is not valid. Check the event log for details. For more information, see Event and Error Handling Under VSS.
VSS_E_OBJECT_NOT_FOUND	The specified item was not found.

Remarks

The caller should free the memory held by the pbstrPath, pbstrFilename, pbstrRange, and pbstrMetadata parameters by calling SysFreeString.

A range indicates a subsection of a given file that is to be backed up, independent of the rest of the file.

The syntax of the range listing (pbstrRanges) is that of a comma-separated list of the form offset1:length1, offset2:length2, where each offset and length is a 64-bit integer specifying a byte offset and length in bytes, respectively. The offset and length can be expressed either as hexadecimal or decimal values.

If pbstrRanges refers to a file containing all the offsets and lengths (a ranges file), pbstrRanges should contain the full path to the file.

If wszRange refers to a file containing all the offsets and lengths (a ranges file), wszRange should contain the full path to the file.

A ranges file must be a binary file with the following format:

A 64-bit integer indicating the number of distinct file ranges that need to be backed up.
Each range expressed as a pair of 64-bit integers: the offset into the file being backed up, in bytes, and the length of data starting from that offset to be backed up.

A ranges file should have been backed up along with the partial file and typically is restored to the same location that it was backed up from.

However, the location to which a ranges file is restored might be altered by the requester, which uses IVssBackupComponents::SetRangesFilePath to indicate this and to update the Backup Components Document so that pbstrRanges indicates the correct ranges file.

A requester would use the ranges information returned by GetPartialFile to restore the backed-up sections to the appropriate location within the copy of the file on disk at restore time.

Requirements

Requirement	Value
Minimum supported client	Windows XP [desktop apps only]
Minimum supported server	Windows Server 2003 [desktop apps only]
Target Platform	Windows
Header	vswriter.h (include Vss.h, VsWriter.h)
Library	VssApi.lib