Return-Path: linux-nfs-owner@vger.kernel.org Received: from mx2.netapp.com ([216.240.18.37]:32786 "EHLO mx2.netapp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752039Ab1JUAH2 convert rfc822-to-8bit (ORCPT ); Thu, 20 Oct 2011 20:07:28 -0400 Subject: Re: Does NFS4 need st_gen? From: Trond Myklebust To: Nikolaus Rath Cc: linux-nfs@vger.kernel.org Date: Thu, 20 Oct 2011 19:07:27 -0500 In-Reply-To: <871uu79z7m.fsf@inspiron.ap.columbia.edu> References: <87ipnlcbg8.fsf@inspiron.ap.columbia.edu> <20111019171551.GA32028@fieldses.org> <87d3dsdcf4.fsf@inspiron.ap.columbia.edu> <20111020120207.GL5444@fieldses.org> <877h3za89w.fsf@inspiron.ap.columbia.edu> <20111020195731.GC9987@fieldses.org> <871uu79z7m.fsf@inspiron.ap.columbia.edu> Content-Type: text/plain; charset="UTF-8" Message-ID: <1319155647.2768.4.camel@lade.trondhjem.org> Mime-Version: 1.0 Sender: linux-nfs-owner@vger.kernel.org List-ID: On Thu, 2011-10-20 at 16:37 -0400, Nikolaus Rath wrote: > "J. Bruce Fields" writes: > > On Thu, Oct 20, 2011 at 01:21:31PM -0400, Nikolaus Rath wrote: > >> I'm working on a FUSE file system that stores file system metadata in an > >> SQL database (http://code.google.com/p/s3ql/). Not having to keep track > >> of inode generation numbers would keep the code much simpler, because I > >> want to delete inode-rows from the SQL table when the last reference to > >> the inode is deleted (so I can't keep track of the generation no). > > > > You can use current time, or a counter, or something, as the generation > > number. > > With current time I'm screwed if the system clock doesn't have > sufficiently fine granularity. With a counter, I either have to remember > counter values per-inode even after the inode is deleted, or the global > counter will overflow at some point (in which case I may just as well > require unique inodes in the first place). The filehandle is between 32 (NFSv2) and 128(NFSv4) bytes long. How long do you expect it to take you to create+destroy between 2^256 and 2^1024 inodes? I'm guessing that we'll all be long dead and the universe will have undergone heat death before that happens... Trond -- Trond Myklebust Linux NFS client maintainer NetApp Trond.Myklebust@netapp.com www.netapp.com