Date: Thu, 15 Feb 2007 15:04:39 +0000 (GMT) From: Robert Watson <rwatson@FreeBSD.org> To: Tomas Olsson <tol@it.su.se> Cc: freebsd-fs@freebsd.org, arla-drinkers@stacken.kth.se Subject: Re: Arla on FreeBSD Message-ID: <20070215150015.O90799@fledge.watson.org> In-Reply-To: <lsr8xez5v15.fsf@kashyyyk.ite.kth.se> References: <20070214162938.GA96725@keira.kiwi-computer.com> <20070214173211.L1054@chrishome.localnet> <20070214170808.GC96725@keira.kiwi-computer.com> <lsrvei45pq1.fsf@kashyyyk.ite.kth.se> <20070215044707.GA39168@deviant.kiev.zoral.com.ua> <lsrmz3f680v.fsf_-_@kashyyyk.ite.kth.se> <20070215104537.GC39168@deviant.kiev.zoral.com.ua> <lsrhctn6393.fsf@kashyyyk.ite.kth.se> <20070215120855.GE39168@deviant.kiev.zoral.com.ua> <lsrd54b603c.fsf@kashyyyk.ite.kth.se> <20070215134608.GG39168@deviant.kiev.zoral.com.ua> <lsr8xez5v15.fsf@kashyyyk.ite.kth.se>
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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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