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Re: Unionmount: proxying the control port

From: olafBuddenhagen
Subject: Re: Unionmount: proxying the control port
Date: Sat, 11 Jul 2009 02:40:49 +0200
User-agent: Mutt/1.5.19 (2009-01-05)


On Fri, Jul 10, 2009 at 12:18:58AM +0300, Sergiu Ivanov wrote:
> On Wed, Jul 08, 2009 at 09:39:06PM +0200, Carl Fredrik Hammar wrote:
> > On Wed, Jul 08, 2009 at 03:41:51PM +0300, Sergiu Ivanov wrote:

> Also note that no other program but nfsd in the Hurd source tree uses
> fsys_getfile and file_getfh (and, consequently, file handles).  Also,
> the content of a file handle seems pretty artificial, so Fredrik posed
> the question whether the concept of a file handle makes much sense at
> all and whether nfsd could be implemented without it.

Well, I don't know exactly why, but I do know that NFS needs some stable
representation of nodes. I remember how in a talk about some Linux
filesystem they said they implemented a two-level structure for the
directory index, with the explicit purpose of getting a stable directory
order for NFS...

> Secondly, nfsd seems to concoct a globally unique thing by maintaining
> such a structure: {filesystem index; file handle} (consider
> hurd/nfsd/cache.c, functions fh_hash and lookup_cache_handle).
> Unfourtunately, unionfs (as well as a number of other translator,
> BTW), gives off ports to the underlying filesystems, too, so this RPC
> cannot be properly implemented.

Is this really a problem? The question is whether nfsd can deal with the
fact that with unionfs, individual files can be supplied by different
file systems, even in a single directory...

(And if it can't in the current implementation, whether this is fixable.)


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