From mboxrd@z Thu Jan 1 00:00:00 1970 From: Benny Halevy Subject: Re: RE: Finding hardlinks Date: Mon, 15 Jan 2007 10:45:07 +0200 Message-ID: <45AB3F13.7010008@panasas.com> References: Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Cc: Spencer Shepler , nfs@lists.sourceforge.net, nfsv4@ietf.org Return-path: To: "Noveck, Dave" , Trond Myklebust In-Reply-To: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: nfsv4-bounces@ietf.org List-ID: How about discussing this topic in the upcoming Connectathon? Benny Noveck, Dave wrote: > For now, I'm not going to address the controversial issues here, > mainly because I haven't decided how I feel about them yet. > > Whether allowing multiple filehandles per object is a good > or even reasonably acceptable idea. > > What the fact that RFC3530 talks about implies about what > clients should do about the issue. > > One thing that I hope is not controversial is that the v4.1 spec > should either get rid of this or make it clear and implementable. > I expect plenty of controversy about which of those to choose, but > hope that there isn't any about the proposition that we have to > choose one of those two. > >> SECINFO information is, for instance, given >> out on a per-filehandle basis, does that mean that the server will > have >> different security policies? > > Well yes, RFC3530 does say "The new SECINFO operation will allow the > client to determine, on a per filehandle basis", but I think that > just has to be considered as an error rather than indicating that if > you have two different filehandles for the same object, they can have > different security policies. SECINFO in RFC3530 takes a directory fh > and a name, so if there are multiple filehandles for the object with > that name, there is no way for SECINFO to associate different policies > with different filehandles. All it has is the name to go by. I think > this should be corrected to "on a per-object basis" in the new spec no > matter what we do on other issues. > > I think the principle here has to be that if we do allow multiple > fh's to map to the same object, we require that they designate the > same object, and thus it is not allowed for the server to act as if > you have multiple different object with different characteristics. > > Similarly as to: > >> In some places, people haven't even started >> to think about the consequences: >> >> If GETATTR directed to the two filehandles does not return the >> fileid attribute for both of the handles, then it cannot be >> determined whether the two objects are the same. Therefore, >> operations which depend on that knowledge (e.g., client side data >> caching) cannot be done reliably. > > I think they (and maybe "they" includes me, I haven't checked the > history > here) started to think about them, but went in a bad direction. > > The implication here that you can have a different set of attributes > supported for the same object based on which filehandle is used to > access the attributes is totally bogus. > > The definition of supp_attr says "The bit vector which would retrieve > all mandatory and recommended attributes that are supported for this > object. The scope of this attribute applies to all objects with a > matching fsid." So having the same object have different attributes > supported based on the filehandle used or even two objects in the same > fs having different attributes supported, in particular having fileid > supported for one and not the other just isn't valid. > >> The fact is that RFC3530 contains masses of rope with which >> to allow server and client vendors to hang themselves. > > If that means simply making poor choices, then OK. But if there are > other cases where you feel that the specification of a feature is simply > > incoherent and the consequences not really thought out, then I think > we need to discuss them and not propagate that state of affairs to v4.1. > > -----Original Message----- > From: Trond Myklebust [mailto:trond.myklebust@fys.uio.no] > Sent: Friday, January 05, 2007 5:29 AM > To: Benny Halevy > Cc: Jan Harkes; Miklos Szeredi; nfsv4@ietf.org; > linux-kernel@vger.kernel.org; Mikulas Patocka; > linux-fsdevel@vger.kernel.org; Jeff Layton; Arjan van de Ven > Subject: Re: [nfsv4] RE: Finding hardlinks > > > On Fri, 2007-01-05 at 10:28 +0200, Benny Halevy wrote: >> Trond Myklebust wrote: >>> Exactly where do you see us violating the close-to-open cache >>> consistency guarantees? >>> >> I haven't seen that. What I did see is cache inconsistency when > opening >> the same file with different file descriptors when the filehandle > changes. >> My testing shows that at least fsync and close fail with EIO when the > filehandle >> changed while there was dirty data in the cache and that's good. > Still, >> not sharing the cache while the file is opened (even on a different > file >> descriptors by the same process) seems impractical. > > Tough. I'm not going to commit to adding support for multiple > filehandles. The fact is that RFC3530 contains masses of rope with which > to allow server and client vendors to hang themselves. The fact that the > protocol claims support for servers that use multiple filehandles per > inode does not mean it is necessarily a good idea. It adds unnecessary > code complexity, it screws with server scalability (extra GETATTR calls > just in order to probe existing filehandles), and it is insufficiently > well documented in the RFC: SECINFO information is, for instance, given > out on a per-filehandle basis, does that mean that the server will have > different security policies? In some places, people haven't even started > to think about the consequences: > > If GETATTR directed to the two filehandles does not return the > fileid attribute for both of the handles, then it cannot be > determined whether the two objects are the same. Therefore, > operations which depend on that knowledge (e.g., client side data > caching) cannot be done reliably. > > This implies the combination is legal, but offers no indication as to > how you would match OPEN/CLOSE requests via different paths. AFAICS you > would have to do non-cached I/O with no share modes (i.e. NFSv3-style > "special" stateids). There is no way in hell we will ever support > non-cached I/O in NFS other than the special case of O_DIRECT. > > > ...and no, I'm certainly not interested in "fixing" the RFC on this > point in any way other than getting this crap dropped from the spec. I > see no use for it at all. > > Trond > > > _______________________________________________ > nfsv4 mailing list > nfsv4@ietf.org > https://www1.ietf.org/mailman/listinfo/nfsv4 _______________________________________________ nfsv4 mailing list nfsv4@ietf.org https://www1.ietf.org/mailman/listinfo/nfsv4