2.3.43 FSCTL_OFFLOAD_WRITE Request
The FSCTL_OFFLOAD_WRITE Request message requests that the server perform an Offload Write operation to a specified portion of a file on a target volume, providing a Token to the server that indicates what data is to be logically written. On the server side, this request is received, processed, and sent to an intelligent storage subsystem that processes the Token and determines whether it can perform the data movement to the requested portion of the file. The Token is generated by an intelligent storage subsystem through an FSCTL_OFFLOAD_READ Request (section 2.3.41) or is constructed as a well-known Token type such as STORAGE_OFFLOAD_TOKEN in section 2.1.11.<41><42>
The request message contains an FSCTL_OFFLOAD_WRITE_INPUT data element, as follows:
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Size |
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Flags |
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FileOffset |
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CopyLength |
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TransferOffset |
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Token (512 bytes) |
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Size (4 bytes): A 32-bit unsigned integer that indicates the size, in bytes, of this data element.
Flags (4 bytes): A 32-bit unsigned integer that indicates the flags to be set for this operation. Currently, no flags are defined. This field SHOULD be set to 0x00000000 and MUST be ignored.
FileOffset (8 bytes): A 64-bit unsigned integer that contains the file offset, in bytes, of the start of a range of bytes in a file at which to begin writing the data logically represented by the Token. The value of this field MUST be greater than or equal to 0x0000000000000000 and MUST be aligned to a logical sector boundary on the volume.
CopyLength (8 bytes): A 64-bit unsigned integer that contains the size, in bytes, of the requested range of the file to write the data logically represented by the Token. The value of this field MUST be greater than or equal to 0x0000000000000000 and MUST be aligned to a logical sector boundary on the volume. This value can be smaller than the size of the data logically represented by the Token.
TransferOffset (8 bytes): A 64-bit unsigned integer that contains the file offset, in bytes, relative to the front of a region of data logically represented by the Token at which to start writing. The value of this field MUST be greater than or equal to 0x0000000000000000 and MUST be aligned to a logical sector boundary on the volume.
Token (512 bytes): A STORAGE_OFFLOAD_TOKEN (section 2.1.11) structure that contains the generated (or constructed) Token to be used as a representation of the data to be logically written. The contents of this field MUST NOT be modified during subsequent operations.