FltSetStreamContext function (fltkernel.h)

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10/21/2021

The FltSetStreamContext routine sets a context for a file stream.

Syntax

NTSTATUS FLTAPI FltSetStreamContext(
  [in]  PFLT_INSTANCE             Instance,
  [in]  PFILE_OBJECT              FileObject,
  [in]  FLT_SET_CONTEXT_OPERATION Operation,
  [in]  PFLT_CONTEXT              NewContext,
  [out] PFLT_CONTEXT              *OldContext
);

Parameters

[in] Instance

An opaque instance pointer for the minifilter driver instance whose context is to be inserted into, removed from, or replaced in the list of contexts attached to the file stream.

[in] FileObject

A pointer to a file object for the file stream.

[in] Operation

Flag specifying details of the operation to be performed. This parameter must be one of the following:

Flag	Meaning
FLT_SET_CONTEXT_REPLACE_IF_EXISTS	If a context is already set for Instance, FltSetStreamContext will replace it with the context specified in NewContext. Otherwise, it will insert NewContext into the list of contexts for the file stream.
FLT_SET_CONTEXT_KEEP_IF_EXISTS	If a context is already set for this Instance, FltSetStreamContext will return STATUS_FLT_CONTEXT_ALREADY_DEFINED, and will not replace the existing context or increment the reference count. If a context has not already been set, the routine will insert NewContext into the list of contexts for the file stream and increment the reference count.

[in] NewContext

A pointer to the new context to be set for the file stream. This parameter is required and cannot be NULL.

[out] OldContext

A pointer to a caller-allocated variable that receives the address of the existing stream context for the Instance parameter, if one is already set. This parameter is optional and can be NULL. For more information about this parameter, see the following Remarks section.

Return value

The FltSetStreamContext routine returns STATUS_SUCCESS or an appropriate NTSTATUS value such as one of the following:

Return code	Description
STATUS_FLT_CONTEXT_ALREADY_DEFINED	If FLT_SET_CONTEXT_KEEP_IF_EXISTS was specified for Operation, this error code indicates that a stream context is already attached to the file stream.
STATUS_FLT_CONTEXT_ALREADY_LINKED	The context pointed to by the NewContext parameter is already linked to an object. In other words, this error code indicates that NewContext is already in use due to a successful prior call of a FltSetXxxContext routine.
STATUS_FLT_DELETING_OBJECT	The instance specified in the Instance parameter is being torn down. This is an error code.
STATUS_INVALID_PARAMETER	An invalid parameter was passed. For example, the NewContext parameter does not point to a valid stream context, or an invalid value was specified for the Operation parameter. This is an error code.
STATUS_NOT_SUPPORTED	The file system does not support per-stream contexts for this file stream. This is an error code.

Remarks

For more information about contexts, see About minifilter contexts.

A minifilter driver calls FltSetStreamContext to attach a stream context to a file stream, or to remove or replace an existing stream context. A minifilter driver can attach one context per minifilter driver instance to the file stream.

FltSetStreamContext cannot be called on an unopened FileObject. Hence it cannot be called from a pre-create callback for a stream because the stream has not been opened at that point. A minifilter driver can, however, allocate and set up the stream context in the pre-create callback, pass it to the post-create callback using the completion context parameter and set the stream context on the stream in the post-create callback.

Reference Counting

If FltSetStreamContext succeeds:

The reference count on NewContext is incremented. When NewContext is no longer needed, the minifilter must call FltReleaseContext to decrement its reference count.

Else if FltSetStreamContext fails:

The reference count on NewContext remains unchanged.
If OldContext is not NULL and does not point to NULL_CONTEXT then OldContext is a referenced pointer to the context currently associated with the stream. The filter calling FltSetStreamContext must call FltReleaseContext for OldContext as well when the context pointer is no longer needed.

Regardless of success:

The filter calling FltSetStreamContext must call FltReleaseContext to decrement the reference count on the NewContext object that was incremented by FltAllocateContext.

For more information, see Referencing Contexts.

Other context operations

For more information, see Setting Contexts, and Releasing Contexts:

To determine whether stream contexts are supported for a given file, call FltSupportsStreamContexts
To allocate a new context, call FltAllocateContext.
To get a stream context, call FltGetStreamContext.
To delete a stream context, call FltDeleteStreamContext or FltDeleteContext.

Requirements

Requirement	Value
Minimum supported client	Available and supported in Microsoft Windows 2000 Update Rollup 1 for SP4, Windows XP SP2, Windows Server 2003 SP1, and later operating systems.
Target Platform	Universal
Header	fltkernel.h (include Fltkernel.h)
Library	FltMgr.lib
DLL	Fltmgr.sys
IRQL	<= APC_LEVEL

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