FltAllocateCallbackDataEx function

Description

The FltAllocateCallbackDataEx routine allocates a callback data structure and can preallocate memory for additional structures that a minifilter driver can use to initiate an I/O request.

Parameters

Instance [in]

Opaque instance pointer to the minifilter driver instance that is initiating the I/O operation. This parameter is required and cannot be NULL.

FileObject [in/optional]

Pointer to a file object to be used in the I/O operation. This parameter is optional and can be NULL. Set FileObject to NULL if this is a CREATE operation.

Flags [in]

A value of zero or the following flag: FLT_ALLOCATE_CALLBACK_DATA_PREALLOCATE_ALL_MEMORY

If this flag is set, the routine preallocates all the memory needed by the filter manager for additional structures to be used in an I/O request.

RetNewCallbackData [out]

Pointer to a caller-allocated variable that receives the address of the newly allocated callback data FLT_CALLBACK_DATA structure.

Return value

The FltAllocateCallbackDataEx routine returns STATUS_SUCCESS on success or STATUS_INSUFFICIENT_RESOURCES if the routine encountered a pool allocation failure when attempting to allocate the callback data structure or if the FLT_ALLOCATE_CALLBACK_DATA_PREALLOCATE_ALL_MEMORY flag is set and additional memory could not be allocated.

Remarks

If the FLT_ALLOCATE_CALLBACK_DATA_PREALLOCATE_ALL_MEMORY flag is set, the routine allocates all the memory needed for additional filter manager structures to be used in a subsequent I/O request. Using this flag enables a minifilter to preallocate one or more callback data structures to be used for issuing I/O requests under low memory conditions or in situations where recovering from a memory allocation failure might be complicated.

[!NOTE] The additional allocated memory is for use by the filter manager. The file system or other filters can still fail the I/O request due to an out-of-memory condition.

[!IMPORTANT] The comments for FltAllocateCallbackData apply to FltAllocateCallbackDataEx as well. Review that information in order to select the correct routine for your design.

See also

FLT_CALLBACK_DATA

FltAllocateCallbackData