Date: Wed, 12 Jul 2000 00:03:23 -0700 (PDT) From: Kelly Yancey <kbyanc@posi.net> To: Marius Bendiksen <mbendiks@eunet.no> Cc: Dmitry Brodsky <dima@cs.ubc.ca>, freebsd-fs@FreeBSD.ORG Subject: Re: Meta-Data & stackable FS Message-ID: <Pine.BSF.4.21.0007112346510.39799-100000@gateway.posi.net> In-Reply-To: <Pine.BSF.4.05.10007112232360.2092-100000@login-1.eunet.no>
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On Tue, 11 Jul 2000, Marius Bendiksen wrote: > > Use the v_data pointer on your vnodes to point to your local meta-data. Now, > > if you need this meta-data to be persistent, that's another matter > > entirely. In that case, you'll probably want to look at umapfs or the quota > > code for reference. > > Absolutely not! > > Persistent metadata should be stuck in the EAs. We have a mechanism for > this, now, so let's not start reinventing the wheel. > So long as you only stack over FFS. As much as I like the idea of extended attributes, stacked file systems should be able to stack over any other filesystem. Unless I'm mistaken, NFS doesn't support EA's, not to mention any of the misc. filesystems. I don't even know where one would begin trying to add EA support to say, procfs. But the man page touches on this, and other valid converns: As there are a plethora of file systems with differing extended attributes, availability and functionality of these functions may be limited, and they should be used with awareness of the underlying semantics of the supporting file system. Authorization schemes for extended attribute data may also vary by file system, as well as maximum attribute size, and whether or not any or specific new attributes may be defined. How could you possibly build a stackable filesystem using EA's when there are so many unknowns except for the degenerate case of "you can stack this filesystem over FFS, or you can't stack it anywhere". And that doesn't even touch the fact that even with FFS, other filesystems can trample on EA's required by your filesystem. The ideas behind EA's are noble, but I can't see using EA's in practice. :( Kelly -- Kelly Yancey - kbyanc@posi.net - Belmont, CA System Administrator, eGroups.com http://www.egroups.com/ Maintainer, BSD Driver Database http://www.posi.net/freebsd/drivers/ Coordinator, Team FreeBSD http://www.posi.net/freebsd/Team-FreeBSD/ To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-fs" in the body of the message
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