Date: Tue, 9 Nov 1999 10:00:20 +0100 From: Jan Pechanec <pechy@hp735.cvut.cz> To: Erez Zadok <ezk@cs.columbia.edu> Cc: freebsd-fs@FreeBSD.ORG Subject: Re: stupidfs - easily extensible test file systems? Message-ID: <Pine.SGI.4.05.9911090953400.5402-100000@akat.civ.cvut.cz> In-Reply-To: <199911051843.NAA21856@shekel.mcl.cs.columbia.edu>
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On Fri, 5 Nov 1999, Erez Zadok wrote: Why I'm interesting in this is that I would like to do something on this as my final work at university. I don't want to include my changes in any OS like FreeBSD or Linux, the work is not intended to be so vast. Maybe I would like to use Minix, it has no VFS etc. so I am free to change what I want and the changes won't be so expensive as they would be in FreeBSD, eg. I would like to try to separate fs into really small layers, ie. UFS can be devided in three layers (disk, inode, dir layer). I am not sure whether it is possible in an efficient way, but I want to try it. I can invent VFS-like interface that would be extensible etc. etc. I know that no of these changes most probably won't appear anywhere, but this is not my goal. I'm just interested. Please, could you comment whether you think it is worth the effort of not? thank you, Jan. >In message <Pine.SGI.4.05.9911051518180.10246-100000@akat.civ.cvut.cz>, Jan Pechanec writes: >> On Thu, 28 Oct 1999, Erez Zadok wrote: >> >> Hi, >> >> I think that it is a bit different. What Robert is hacking is >> a filesystem where in-vfs-not-experienced programmer can see how vfs >> is working. I have just read some of your papers, Erez, and I think >> that wrapfs wants me not to bother with something like vfs (just >> encode and decode routines). > >The encode and decode routines that wrapfs exports are an API that greatly >simplifies two difficult tasks: > >(1) modifying file names (e.g., translating b/t unix and 8.3 names) >(2) modifying file data (e.g., encryption) > >Every other task you want to accomplish in wrapfs, you do it right in the >actual f/s routines, right in the code itself. For example, if you wanted >to add acl support (as I've done w/ a trivial aclfs based on wrapfs), you >add the right code in lookup(). If you want to create an unrmfs (another >prototype I've got), you add it in unlink(). If you wish, you can also >touch the read/write/getpage/putpage routines directly and not use the >encode/decode API functions. But you'll find that there's a substantial >amount of support code needed to deal with data pages, locking, and a lot >more stuff around it. All of this is detailed in my Usenix 99 paper. > >> I think that Robert's effort is very useful, I wanted myself >> to write somethink like this (purpose: to learn and _touch_ vfs >> interface). Robert, do you carry on or not? > >I commend you, but don't be surprised if what you'll produce in the end will >be almost identical to wrapfs in functionality. It many ways, wrapfs is >"stupid", b/c it only provides a thin layer that passes all VOPs to the >layer below it, while maintaining semantics. Wrapfs does not do much more >than that. That's why I'm telling you now that your stupidfs may wind up >being very similar to wrapfs. You cannot get stacking functionality with >much less than wrapfs does. > >If you actually intend to modify the VFS, and add new VOPs, that'll be neat >too. But I think you'll find it a bit difficult to get VFS changes merged >into the main source tree... :-) And if you will change the VFS, you'll find >that your stupidfs does more than, and is "smarter" than wrapfs. > >You cannot introduce new VOPs w/o changing the VFS, and if you change the >VFS, you must make sure that other (native) file systems do something >reasonable with these new VOPs. > >> -- >> Jan PECHANEC (mailto:pechy@hp735.cvut.cz) Computing Center CTU (Zikova 4, >> Praha 6, 166 35, Czech Republic) http://www.civ.cvut.cz, tel: +420 2 2435 >> 2969, http://pechy.civ.cvut.cz > >Jan et al. I'm not trying to "hawk my merchandise" on you, but rather to >save you a great deal of effort repeating that which has been done before. >I've created and released my wrapfs templates so that others could build on >them, and create hopefully really useful (even commercial) file systems. It >may sound corny, but I hope that my work will revitalize the stagnating >field of stackable file systems research. You may save a lot of time, and >still be able to learn much, by starting with my wrapfs code, and modifying >it to your needs. I will be happy to help you in any way I can. > >Cheers, >Erez. > > >To Unsubscribe: send mail to majordomo@FreeBSD.org >with "unsubscribe freebsd-fs" in the body of the message > -- Jan PECHANEC (mailto:pechy@hp735.cvut.cz) Computing Center CTU (Zikova 4, Praha 6, 166 35, Czech Republic) www.civ.cvut.cz, pechy.civ.cvut.cz, tel: +420 2 24352969 (fax: 24310271) To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-fs" in the body of the message
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