What does NTSTATUS 0xC01C0008 (STATUS_FLT_FILTER_NOT_READY) mean?

 
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STATUS_FLT_NOT_INITIALIZED STATUS_FLT_POST_OPERATION_CLEANUP

STATUS_FLT_FILTER_NOT_READY

STATUS_FLT_FILTER_NOT_READY identifies a specific stage between registration and activation. The minifilter has not completed the transition made by FltStartFiltering, so it is not ready to attach to volumes or receive filtering work.

The correct fix is sequencing, not a retry loop around an arbitrary volume. Initialize global resources, register callbacks and contexts, then call FltStartFiltering. Once that call starts, Filter Manager can present volumes and I/O before it returns, so every resource used by those callbacks must already be ready.

Distinguish the lifecycle states

  • Not initialized: Filter Manager itself was unavailable for registration.
  • Not ready: the minifilter exists but has not begun filtering.
  • Deleting object: an active filter or volume is already being torn down.

FltStartFiltering | FltAttachVolumeAtAltitude | NTSTATUS reference


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