Re: [patch 1/4] Add routine for generating an ID for kernel pointer

From: Cyrill Gorcunov
Date: Sat Dec 31 2011 - 02:51:33 EST

On Fri, Dec 30, 2011 at 06:51:37PM -0500, KOSAKI Motohiro wrote:
> >
> >Guys, this become more and more complex, finally I fear someone
> >propose to do ideal hashing run-time ;) Maybe we can step back and
> >live with root-only and plain pointers here? I'm not sure who else
> >might need such facility except us, and if once there will be a candidate
> >-- we could take a look on hashing again and provide safe hashes there. No?
> But recently kernel security fashion are, we don't expose a kernel
> pointer at all even though the file is root only. I'm not sure how
> much effective such fashion. but you seems run opposite way.
> I doubt user land can implement good comparison way. Why you gave up
> Andrew's sys_are_these_files_the_same() idea?

Because of speed, as Pavel mentioned
| With this the complexity of determining sharing for N files scattered across
| several tasks would be N^2, since we'll have to compare each file to each file.
| On the other hand having just N IDs at hands would allow us to use more
| efficient algorithms resulting in e.g. N*log(N) complexity.

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