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Date:      Wed, 28 Mar 2007 14:54:42 +0200
From:      Ivan Voras <ivoras@fer.hr>
To:        Greg Troxel <gdt@ir.bbn.com>
Cc:        freebsd-fs@freebsd.org
Subject:   Re: TDFS ... or other distributed file system technologies for	FreeBSD?
Message-ID:  <460A6592.3040308@fer.hr>
In-Reply-To: <rmi7it11rgi.fsf@fnord.ir.bbn.com>
References:  <4746DA006C148BC0FF1241C6@ganymede.hub.org>	<euberg$f1u$1@sea.gmane.org>	<45CCECCB7ECB612F504211F3@ganymede.hub.org>	<eubmlt$fgp$1@sea.gmane.org> <rmi7it11rgi.fsf@fnord.ir.bbn.com>

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Greg Troxel wrote:

> I've been playing with Coda for a long time, originally in FreeBSD
> 2.2, 3 and 4, and more recently in NetBSD.  My problems have been all
> correctness issues, both in coda's handling of conflicts and in the
> kernel vfs locking code.  Coda has not yet worked reliably enough that
> I've been worried about performance.  Once you put a network and
> another system in the path, the round trip to user space is not that
> big a deal.

Yes, I suspected that locking will one of the big problems.

> It is truly hard to get the vfs locking issues right (lock one vnode,
> release another, do it in the right order, reference counts, follow
> the rules exactly).  FUSE should (and probably is) taking care of this
> for you.

Yes, but it doesn't support file locking (flock()), which is kind of=20
required for serious work.

> The other thing people could do is import puffs and librefuse from
> NetBSD (also originally an SoC project).  puffs is like FUSE, but aims
> to be a richer interface.  librefuse uses puffs to provide a
> FUSE-compatible interface, so you can run FUSE filesystems linked
> against librefuse, and there's no GPL/LGPL code in the base system.

Interesting. I'll look into that. It's too late for SoC but it's nice=20
having something like it.

> Porting it to FreeBSD should mostly be straightforward, but I think
> the VFS locking rules have diverged, particularly in how .. locking is
> handled in vfs_lookup.  So making puffs work in FreeBSD will require
> cycles from someone who groks the vfs layer.

Thanks for the information.


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