store pointer in process structure?

Does anyone know how to save a context information of file system
driver in process structure. Is there a unused field in process
structure that driver can make use of. IoSetTopLevelIrp() wont help me
cause the context information remains forever till the process

Also is there way to directly send UDP packets without using IRPs. Why
TDI drivers dont have FASTIO dispatch routines?

thanks for any help

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