IVssComponent::AddPartialFile method (vswriter.h)

Article
10/13/2021

The AddPartialFile method indicates that only portions of a given file are to be backed up and which portions those are.

Only a writer can call this method, and only during a backup operation.

Syntax

HRESULT AddPartialFile(
  [in] LPCWSTR wszPath,
  [in] LPCWSTR wszFilename,
  [in] LPCWSTR wszRanges,
  [in] LPCWSTR wszMetadata
);

Parameters

[in] wszPath

Null-terminated wide character string containing the path of the file involved in partial file operations.

The path can contain environment variables (for example, %SystemRoot%) but cannot contain wildcard characters.

There is no requirement that the path end with a backslash (""). It is up to applications that retrieve this information to check.

This path should match or be beneath the path of a file set already in the component (or one of its subcomponents if the component defines a component set).

[in] wszFilename

Null-terminated wide character string containing the name of the file involved in partial file operations. The name of the file (wszFilename) cannot contain wildcard characters (* or ?) and must be consistent with the file specification of a file set containing the source path (wszPath).

[in] wszRanges

Null-terminated wide character string containing either a listing of file offsets and lengths that make up the partial file support range (the sections of the file to actually be backed up), or the name of a file containing such a list.

Specifying the partial file support range is required, and this value cannot be NULL.

[in] wszMetadata

Null-terminated wide character 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.

If additional metadata is not required, this value can be NULL.

Return value

The following are the valid return codes for this method.

Value	Meaning
S_OK	Successfully set the item.
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 method was not called by a writer or, if called by a writer, was not called during a restore operation.

Remarks

Only a writer can call this method, and the writer cannot call this method during a restore operation.

The syntax of the range listing (wszRanges) 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 wszRange refers to a file containing all the offsets and lengths (a ranges file), wszRange will contain only 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

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

Requesters can retrieve the partial file information using IVssComponent::GetPartialFile and use the offset and length information returned by GetPartialFile to restore backed-up sections to the appropriate location within the copy of the file on disk at restore time.

AddPartialFile can be applied to a file already managed by the component (or one of its subcomponents if the component defines a component set), or it can add a new file to the component and indicate that it will participate in partial file operations.

When indicating that the file to participate is a new file, that file must exist on a shadow-copied volume and its path (wszPath) should match or be beneath a path already in the component (or one of its subcomponents if the component defines a component set). However, the file's file specification (wszFileSpec) should not match one in the components.

Any newly added files will not support alternate location mappings.

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