FLT_CONTEXT_REGISTRATION structure (fltkernel.h)

The FLT_CONTEXT_REGISTRATION structure is used to register context types.

Syntax

typedef struct _FLT_CONTEXT_REGISTRATION {
  FLT_CONTEXT_TYPE               ContextType;
  FLT_CONTEXT_REGISTRATION_FLAGS Flags;
  PFLT_CONTEXT_CLEANUP_CALLBACK  ContextCleanupCallback;
  SIZE_T                         Size;
  ULONG                          PoolTag;
  PFLT_CONTEXT_ALLOCATE_CALLBACK ContextAllocateCallback;
  PFLT_CONTEXT_FREE_CALLBACK     ContextFreeCallback;
  PVOID                          Reserved1;
} FLT_CONTEXT_REGISTRATION, *PFLT_CONTEXT_REGISTRATION;

Members

ContextType

The type of context. This member is required and must be one of the following values:

FLT_FILE_CONTEXT (Windows Vista and later only.)

FLT_INSTANCE_CONTEXT

FLT_STREAM_CONTEXT

FLT_STREAMHANDLE_CONTEXT

FLT_SECTION_CONTEXT (Windows 8 and later only.)

FLT_TRANSACTION_CONTEXT (Windows Vista and later only.)

FLT_VOLUME_CONTEXT

Flags

A bitmask of flags that specify how the filter manager allocates a new context from a lookaside list of fixed-size contexts. This member can be zero or the following value.

ContextCleanupCallback

A pointer to a minifilter-defined ContextCleanupCallback routine of type PFLT_CONTEXT_CLEANUP_CALLBACK. The filter manager calls this routine immediately before it deletes the context. If the minifilter has no memory or pointers to clean up inside the context, this member is optional and can be NULL.

Size

The size, in bytes, of the minifilter-defined portion of the context, if the minifilter uses fixed-size contexts. Zero is a valid size value. If the minifilter uses variable-size contexts, this member is required and must be set to FLT_VARIABLE_SIZED_CONTEXTS.

PoolTag

A pool tag value to be used for the context. This tag, which is specified as a string of one to four 7-bit ASCII characters, appears in any crash dump of the system that occurs. If the ContextAllocateCallback member is NULL, this member is required and cannot be zero.

ContextAllocateCallback

Pointer to a minifilter-defined ContextAllocateCallback routine of type PFLT_CONTEXT_ALLOCATE_CALLBACK. This member is optional and can be NULL. If it is not NULL, the Size and PoolTag members are ignored.

ContextFreeCallback

A pointer to a minifilter-defined ContextFreeCallback routine of type PFLT_CONTEXT_FREE_CALLBACK. This member is optional and can be NULL. If it is not NULL, the Size and PoolTag members are ignored.

Reserved1

Reserved for system use. Minifilters must set this member to NULL.

Remarks

When a minifilter calls FltRegisterFilter from its DriverEntry routine, it must register each context type that it uses.

To register these context types, the minifilter creates a variable-length array of FLT_CONTEXT_REGISTRATION structures and stores a pointer to the array in the ContextRegistration member of the FLT_REGISTRATION structure that the minifilter passes as the Registration parameter of FltRegisterFilter. The last element of this array must be {FLT_CONTEXT_END}.

For each context type that the minifilter uses, the minifilter must supply at least one FLT_CONTEXT_REGISTRATION structure, according to the following rules:

• If the minifilter supplies an FLT_CONTEXT_REGISTRATION structure with a non-NULL ContextAllocateCallback member, it cannot supply any additional FLT_CONTEXT_REGISTRATION structures for that context type.
• If the minifilter supplies two or more identical FLT_CONTEXT_REGISTRATION structures, only the first one will be used. The others will be ignored.
• Only one FLT_CONTEXT_REGISTRATION structure with a Size member of FLT_VARIABLE_SIZED_CONTEXTS can be supplied for each context type.
• No more than three FLT_CONTEXT_REGISTRATION structures with a Size member other than FLT_VARIABLE_SIZED_CONTEXTS can be supplied for each context type.

Requirements

See also

FLT_REGISTRATION

FltRegisterFilter

PFLT_CONTEXT_ALLOCATE_CALLBACK

PFLT_CONTEXT_CLEANUP_CALLBACK

PFLT_CONTEXT_FREE_CALLBACK