OffloadWriteFile Event

Fires when the OS wants the virtual filesystem to perform an offloaded data transfer (ODX) write operation.


virtual int FireOffloadWriteFile(CBFSOffloadWriteFileEventParams *e);
typedef struct {
const char *FileName;
int64 Position;
int64 CopyLength;
int64 TransferOffset;
int64 *pTransferLength;
int TokenType;
const void *Token;
int64 TokenLength;
int ResultFlags;
int64 HandleInfo;
void *FileContext;
void *HandleContext;
int ResultCode; int reserved; } CBFSOffloadWriteFileEventParams;
virtual INT FireOffloadWriteFile(CBFSOffloadWriteFileEventParams *e);
typedef struct {
LONG64 Position;
LONG64 CopyLength;
LONG64 TransferOffset;
LONG64 *pTransferLength;
INT TokenType;
LONG64 TokenLength;
INT ResultFlags;
LONG64 HandleInfo;
LPVOID FileContext;
LPVOID HandleContext;
INT ResultCode; INT reserved; } CBFSOffloadWriteFileEventParams;


This event fires when the OS wants the virtual filesystem to perform an offload write for the file specified by FileName as part of an offloaded data transfer.

To handle this event properly, applications should perform any actions needed to handle the offloaded write based on the specified parameters, and then return the result information. Please refer to the parameter descriptions below for more information.

The Position and CopyLength parameters specify the byte offset and length (respectively) of the data chunk that should be written in the specified file. The CopyLength parameter's value may be smaller than the total amount of data represented by the token (in which case TransferOffset may be greater than 0).

The TransferOffset parameters specifies the byte offset, in the chunk of data represented by the token, from which to begin writing.

The TransferLength parameter must be set to the number of bytes actually written as a result of this request. It may be less than CopyLength.

The TokenType parameter indicates the type of token stored in the Token buffer. A value of STORAGE_OFFLOAD_TOKEN_TYPE_ZERO_DATA (0xFFFF0001) indicates that the token represents data which is all zeros; while any other value (outside of the reserved range 0xFFFF0002 to 0xFFFFFFFF) indicates an application-defined token format.

The Token parameter points to a memory buffer that contains the token returned in response to an earlier offload read request. The token identifies the chunk of data that has been read/prepared for transfer; refer to the OffloadReadFile event for more information. The TokenLength parameter specifies the length, in bytes, of the data in Token.

Please refer to the Buffer Parameters topic for more information on how to work with memory buffer event parameters.

The ResultFlags parameter must be set to a combination of zero or more of the flags described in the FSCTL_OFFLOAD_WRITE_OUTPUT structure's documentation.

The HandleInfo parameter carries a handle to an object with information about the file handle. While within the event handler, it can be used to call any of the following methods: GetHandleCreatorProcessId, GetHandleCreatorProcessName, GetHandleCreatorThreadId, or GetHandleCreatorToken. (This parameter may be absent, in which case it will be 0.)

The FileContext and HandleContext parameters are placeholders for application-defined data associated with the file and specific handle, respectively. Please refer to the Contexts topic for more information. (HandleContext may be absent, in which case it will be NULL.)

The ResultCode parameter will always be 0 when the event is fired. If the event cannot be handled in a "successful" manner for some reason (e.g., a resource isn't available, security checks failed, etc.), set it to a non-zero value to report an appropriate error. Please refer to the Error Reporting and Handling topic for more information.

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CBFS Connect 2020 C++ Edition - Version 20.0 [Build 7545]