Date: Thu, 7 Jan 1999 02:31:04 +0000 (GMT) From: Terry Lambert <tlambert@primenet.com> To: Don.Lewis@tsc.tdk.com (Don Lewis) Cc: dyson@iquest.net, tlambert@primenet.com, dillon@apollo.backplane.com, pfgiffun@bachue.usc.unal.edu.co, freebsd-hackers@FreeBSD.ORG Subject: Re: questions/problems with vm_fault() in Stable Message-ID: <199901070231.TAA08668@usr09.primenet.com> In-Reply-To: <199901062244.OAA01922@salsa.gv.tsc.tdk.com> from "Don Lewis" at Jan 6, 99 02:44:47 pm
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> } Subject: Re: questions/problems with vm_fault() in Stable > > } Any of the problems with the existing VFS/VM scheme have been with the > } intricacies of dealing with VFS special cases, and dealing with the > } I/O abstraction of buffers as a cache. Forget "files" and think > } "blobs of memory." Once the notion of file is forgotten, then shadowing, > } invalidation and aliasing of memory become very obvious... [ ... ] > Maybe the thing to do is to turn all the filesystems into stacking > layers, including ffs. UFS *is* a stacking layer that imposed directory hierarchy on FFS. The complication doesn't arise (i.e., FFS works despite generalized stacking being shot in the head from day one of the 4.4 integration) because *the same set of vnodes are used at the same level for both layers*. This is tantamount to there being implicit object coherency between the layers. We know that implicit object coherency between stacking layers would work because we have this example where it *does* work. Put another way, any method that results in a umapfs with *any* implementations for anything other than credential-containing VOP descriptors is wrong (the VOP_BYPASS stuff is a crock; it results from some side-effects that are gratuitous. See the null_bypass() code for details on this; if SunOS can do it right, *BSD can damn well do it right). Terry Lambert terry@lambert.org --- Any opinions in this posting are my own and not those of my present or previous employers. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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