packet_mmap: How to kernel address from user-space address

[selvamuthukumar v]

I'm trying to accelerate snort with a hardware Pattern Matching Engine.
snort gets packets using libpcap which uses packet mmap. snort gets the
mmap-ed address, it does all header parsing, now I want to offload the
content detection to hardware. PME driver currently provides and ioctl
interface to pass the packet. Driver does copy_from_user to get packet data
to kernel and try to match it against pre-loaded contents. I'm trying to
avoid this copy. What is the best way to get the kernel address from user
address in this case?
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