2.3.65 FSCTL_SET_SPARSE Request

This message requests that the server mark the file that is associated with the handle on which this FSCTL was invoked as sparse. In a sparse file, large ranges of zeros (0) might not require disk allocation. Space for nonzero data is allocated as the file is written. The message either has no data elements at all or it contains a FILE_SET_SPARSE_BUFFER element. If there is no data element, the sparse flag for the file is set, exactly as if the FILE_SET_SPARSE_BUFFER element was supplied and had a SetSparse value of TRUE.<58>

The FILE_SET_SPARSE_BUFFER element is as follows:


0


1


2


3


4


5


6


7


8


9

1
0


1


2


3


4


5


6


7


8


9

2
0


1


2


3


4


5


6


7


8


9

3
0


1

SetSparse

SetSparse (1 byte): A Boolean (section 2.1.8) value.

A FALSE value will cause the file system to attempt to "unsparse" the file by allocating clusters for any regions of the file that are currently sparsed. If the entire file is successfully unsparsed, the sparse flag is cleared for the file. If an error is encountered during unsparsing, any regions of the file that were unsparsed MAY<59> remain unsparsed.

A TRUE value will cause the sparse flag for the file to set. Currently allocated clusters SHOULD NOT<60> be deallocated.

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