Subject: Re: nfs optimization and veriexec
To: Elad Efrat <>
From: Brett Lymn <>
List: tech-kern
Date: 12/18/2007 15:53:21
On Tue, Dec 18, 2007 at 12:23:25AM +0200, Elad Efrat wrote:
> Okay. I gave this some thought. First, I think we need to better define
> the interaction between NFS (and probably remote file-systems in
> general) and Veriexec. IIRC, we did this a long time ago, but we
> really should make it clear and documented. We're also missing the
> per-page fingerprints that make it "easier to trust" files from a system
> you have no control over.

There are two sides to the NFS equation when it comes to veriexec:

1) Server side, this presents some issues because we usually hook into
   the VOP layer for read/write checking.  Unfortunately the NFS
   server does not use the VOP calls when it gets read/write requests,
   the server code pages the requested part of the file into memory
   and then pushes it out to the client.  From (possibly incorrect)
   memory, the open code path is different to most other file systems

2) Client side, does use the VOP calls so the veriexec checks should
   just work but with the caveat that the server needs to be trusted

I am sure that the per-page checking I would like to get in would
address the issues on both sides.  I need to get back to the unified
iodone call - after talking with Chuck a while back I understand
things a bit better, I need to update my tree and push another patch

Brett Lymn
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