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I have a layered file system (implemented as a minifilter) which provides cache manager integration. I'm struggling to understand if there is a workable solution for receiving oplock breaks for the underlying CIFS files. Years ago I understood the answer to be "no" going off of info provided in posts such as these: https://community.osr.com/discussion/171306/intercepting-oplock-requests-in-a-minifilter
But recently, while stepping through rdbss internals I came across FsRtlUpperOplockFsctrl() for the first time (apparently introduced with Win 8.1). When I open the CIFS target file and then send an FSCTL_REQUEST_OPLOCK down (using FltPerformAsynchronousIo so I can register a completion callback) I always get a status of STATUS_OPLOCK_NOT_GRANTED in my callback. Stepping through rdbss!RxOplockRequest() I see that it is passing my IRP along with its own oplock to FsRtlUpperOplockFsctrl(). That function is returning the STATUS_OPLOCK_NOT_GRANTED which is getting passed along to my callback.
The documentation for FsRtlUpperOplockFsctrl and FsRtlCheckUpperOplock both explicitly say they are designed to allow oplock checking in layered file systems. But will these work in my scenario and with CIFS specifically? I cannot find any mention of the APIs on these forums, or in github examples, or anywhere other than the two MSDN pages.
I think it is clear, but for the inevitable "what are you trying to do?" question, I'm needing to invalidate my caching of a CIFS file on host 1 when an update on host 2 breaks the oplock. Rdbss itself would know about this, but it isn't the layer providing the cache manager integration.
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