TXN_PARAMETER_BLOCK structure (ntddk.h)

The TXN_PARAMETER_BLOCK structure contains information about a transacted file operation.

Syntax

typedef struct _TXN_PARAMETER_BLOCK {
  USHORT Length;
  USHORT TxFsContext;
  PVOID  TransactionObject;
} TXN_PARAMETER_BLOCK, *PTXN_PARAMETER_BLOCK;

Members

Length

The size, in bytes, of the TXN_PARAMETER_BLOCK structure.

TxFsContext

The miniversion ID for the file.

TransactionObject

An opaque pointer to the transaction object for the transaction.

Remarks

A miniversion is a version of a file that a transacted writer creates during a transaction. (A transacted writer is a transacted file handle opened with any permission that is not part of generic read access, but is part of generic write access.)

If a specific miniversion number for the file is not provided, the TxFsContext member must be set to TXF_MINIVERSION_DEFAULT_VIEW.

The TxFsContext member of the TXN_PARAMETER_BLOCK uses TXF_MINIVERSION_DEFAULT_VIEW to get the default view of the requested file that is based on the value of the TransactionObject member. So if TransactionObject is the same transaction that has the requested file locked for transacted modification, the caller can see those modifications (the "dirty" view of the file) if the caller can specify the value of the TransactionObject member. If TransactionObject is not the same transaction that has the requested file locked for transacted modification, the caller gets a transactionally isolated view of the file if it specifies this value.

A miniversion exists only as a point-in-time view of a file and has not yet been written as an actual on-disk variant of a given file. A transacted writer creates a miniversion by using the FSCTL_TXFS_CREATE_MINIVERSION control code to call ZwFsControlFile. In response, the system creates a miniversion and returns its miniversion ID. The transacted writer can continue to make changes to the file thereafter. If the file is opened later by using the returned miniversion ID as the TxFsContext member of the TXN_PARAMETER_BLOCK structure, the resulting file handle shows the file as it was at the time that miniversion was created.

All miniversions created in a transaction go away when the transaction ends. Afterwards, the file can no longer be opened by using the miniversion IDs.

A miniversion is available only to the transacted writer that created the miniversion, not to a transacted reader or non-transacted reader.

The IoGetTransactionParameterBlock routine returns a pointer to this structure.

Requirements

Requirement	Value
Header	ntddk.h (include Ntddk.h, Ntifs.h, FltKernel.h)

See also

FSCTL_TXFS_CREATE_MINIVERSION

IoGetTransactionParameterBlock

ZwFsControlFile