Date: Mon, 9 Mar 1998 15:21:25 +0200 From: Anatoly Vorobey <mellon@pobox.com> To: current@FreeBSD.ORG Subject: Re: vnode_pager: *** WARNING *** stale FS code in system Message-ID: <19980309152125.08053@techunix.technion.ac.il> In-Reply-To: <199803090344.UAA17601@usr08.primenet.com>; from Terry Lambert on Mon, Mar 09, 1998 at 03:44:12AM %2B0000 References: <199803090300.UAA13920@mt.sri.com> <199803090344.UAA17601@usr08.primenet.com>
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Probably a silly question, but still: You, Terry Lambert, were spotted writing this on Mon, Mar 09, 1998 at 03:44:12AM +0000: > > (BTW, can you describe succintly what a 'local media' FS is in your > > terms, so that I'm not making any wrong assumptions?) > > A file system is stackable if it both provides and consumes the VFS > interface. NULLFS is an example of a stackable FS. > > A file system is not stackable if it provides the VFS interface, but > consumes another interface (such as the local OS's VM system). FFS is > an example of a non-stackable FS which consumes another interface. > > A file system is not stackable if it does not provide the VFS interface, > even if it consumes the VFS interface. The NFS server is an example of > a non-stackable VFS consumer. The FreeBSD system call interface is another > example of a non-stackable VFS consumer. What about the NFS as a whole? It's both a provider and a consumer of VFS. Does it mean it's a stackable FS? (forgetting for a moment the networking details; e.g. export and mount a local filesystem for proof of concept). And if it does, how does it manage to exist if you're saying a lot of work has to be done to make stackable FSs possible? Another question: which OSes _today_ provide for stackable file systems? Not FreeBSD, apparently not Linux or Solaris. NT has got "filesystem filters" kind of drivers which stack above the FS (and on each other if needed) - this is neat and often useful - but hasn't got stackable filesystems IIRC. A third question: can you give a (few?) example(s?) of hypothetical useful stackable file systems, besides NULLFS? Thanks in advance for your patience. -- Anatoly Vorobey, mellon@pobox.com http://pobox.com/~mellon/ "Angels can fly because they take themselves lightly" - G.K.Chesterton To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-current" in the body of the message
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