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ERROR_FLT_DUPLICATE_ENTRY
Each operation receives one registration record
ERROR_FLT_DUPLICATE_ENTRY indicates that the operation registration supplied to Filter Manager contains conflicting definitions for the same major function. The FLT_OPERATION_REGISTRATION array is not an ordered chain of handlers: one entry supplies the pre-operation callback, post-operation callback, and flags for one operation code.
Duplicate entries often appear when feature-specific registration arrays are concatenated or generated conditionally. Filter Manager cannot infer which flags or callback pair should win, so registration fails rather than silently selecting one. Combine the behavior behind a single dispatch callback or build one canonical entry after resolving feature flags.
How to find the collision
- Dump every major function in the final array passed to
FltRegisterFilter. - Check build-time feature branches that may append the same operation twice.
- Verify that the array ends with one
IRP_MJ_OPERATION_ENDsentinel. - Merge callback logic explicitly instead of relying on duplicate-array order.
References
- Microsoft: operation registration array format
- Microsoft: minifilter registration validation
- Microsoft Open Specifications: STATUS_FLT_DUPLICATE_ENTRY
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