[4173] in arla-drinkers
Re: Arla on FreeBSD
daemon@ATHENA.MIT.EDU (Robert Watson)
Thu Feb 15 10:05:06 2007
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Date: Thu, 15 Feb 2007 15:04:39 +0000 (GMT)
From: Robert Watson <rwatson@FreeBSD.org>
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To: Tomas Olsson <tol@it.su.se>
Subject: Re: Arla on FreeBSD
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On Thu, 15 Feb 2007, Tomas Olsson wrote:
>> Also, you could look at file handle API, that would save you of path
>> lookups after the vnode is looked up first time (look around for vfs_vptofh
>> and vfs_fhtovp ops). This API is used by NFS server, so it shall work :).
>>
> That's an idea. We used that before in another context, but then we ran into
> trouble with too many OSes so we dropped it. Depends on how much code one
> can share.
It has been ages since I looked at the xfs/nnpfs internals, but I thought it
already used file handles to identify cache files to the kernel? I seem to
recall several of our fh*() system calls were added by Assar specifically in
support of Arla work.
With regard to cache files -- historically (i.e., last time I looked closely),
there was a one-to-one mapping between cache files and files in the Arla
working set, and all files were transfered "whole" into the local cache.
This was in contrast to AFS's chunking behavior. I assume the cache file
changes to support "lines" in the cache are in support of adding chunking to
Arla. Is it the case that one file visible in /afs may now be backed by pages
coming from different cache files? How does this interact with the vnode
pager? I assume you actually end up with two pagers -- one for the file as
visible in /afs, and then satisfy the pager's VOP requests by forwarding them
to the right one of the cache vnodes? I trust you don't mmap the cache vnode,
which would lead to cache consistency issues between any mappings of the /afs
vnode vs the cache vnode?
Any chance we could attract you to BSDCan to meet in person to discuss this?
:-)
Thanks,
Robert N M Watson
Computer Laboratory
University of Cambridge
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