Date: Fri, 20 Jun 2003 10:55:48 +0200 From: "Poul-Henning Kamp" <phk@phk.freebsd.dk> To: Donn Miller <dmmiller@cvzoom.net> Cc: fs@freebsd.org Subject: Re: ideas about a unioning file system Message-ID: <7880.1056099348@critter.freebsd.dk> In-Reply-To: Your message of "Fri, 20 Jun 2003 04:50:57 EDT." <3EF2CAF1.4080605@cvzoom.net>
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In message <3EF2CAF1.4080605@cvzoom.net>, Donn Miller writes: >David Schultz wrote: > >> Unionfs in FreeBSD has a number of implementation issues. Many of >> these stem out of locking problems and the fact that VFS layering >> doesn't really work right in FreeBSD. These are fixable details, >> and perhaps FiST addresses some of these. > >That's one thing I was curious about. Is there a need to redo the VFS >layer in FreeBSD? Someone mentioned it as a possible to-do item. If >so, would it make it easier to port new filesystems to FreeBSD? There are certainly deficiencies in our VFS layer, but nothing compared to our other challenges, so unless some external factor makes an up/down/side-grade a good idea, I think we should focus on making it work as it is. The majority of the problems we have in this area can be nailed down to only two issues: 1. The very tricky semantics of rename(2) 2. read/write/mmap coherency for stacked filesystems. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 phk@FreeBSD.ORG | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence.
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