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Path: sserve!newshost.anu.edu.au!harbinger.cc.monash.edu.au!bunyip.cc.uq.oz.au!munnari.oz.au!news.hawaii.edu!ames!hookup!olivea!gossip.pyramid.com!sun.digidesign.com!netcomsv!netapp.com!netapp.com!not-for-mail From: guy@netapp.com (Guy Harris) Newsgroups: comp.unix.bsd Subject: Re: Why select() returns ``exceptional'' for files? Date: 28 Jan 1995 21:06:35 -0800 Organization: Network Appliance Corporation Lines: 36 Message-ID: <3gf7or$3k2@nova.netapp.com> References: <3fois1$5d5@shore.shore.net> <bakulD2wLz4.5Gn@netcom.com> <3g65hg$2ns@nova.netapp.com> <bakulD33vxv.KIt@netcom.com> NNTP-Posting-Host: 192.9.200.13 Bakul Shah <bakul@netcom.com> wrote: >guy@netapp.com (Guy Harris) writes: >>That way, the issue of select-on-exceptional-condition on files, and of >>changes to the NFS protocol to do stronger cache consistency (which is >>what eliminating polling for this case really implies, as far as I can >>tell), are decoupled - which, as far as I'm concerned, is as it should >>be, as there's no reason to deny people any benefits that might accrue >>from select-on-exceptional-condition on files merely because we don't >>have strong(er) cache consistency for NFS. > >I don't know. Seems to me that if there was a protocol that did >cache consistency, select-on-exceptional-condition-on-files >(SOECOF) would be almost for free. That's not a reason to deny people any benefits that might accrue from select-on-exceptional-condition on files merely because we don't have strong(er) cache consistency for NFS. SOECOF on NFS is probably easier to implement than real cache consistency for NFS, and doesn't require you to design a protocol and get all the NFS client and server vendors to implement it. I.e., the fact that SOECOF would come for free *if* you had real cache consistency isn't really relevant here, given that: 1) it wouldn't really come for free, given that the vast majority of NFS servers aren't likely to implement a real cache consistency protocol tomorrow, so, unless you want to render applications that use SOECOF unusable over NFS (which may keep people from using SOECOF in their applications), you'll have to implement it over Boring Old NFS V2 and Boring Old NFS V3 anyway; 2) there's probably enough work involved in designing a real cache consistency protocol for NFS *and* getting it adopted that "for free" is somewhat misleading.