From: Bernd Schubert Subject: Re: Extended file stat: Splitting file- and fs-specific info? Date: Wed, 09 May 2012 16:12:57 +0200 Message-ID: <4FAA7B69.7060300@itwm.fraunhofer.de> References: <20120509002420.GL5091@dastard> <20120419140558.17272.74360.stgit@warthog.procyon.org.uk> <16281.1336508382@redhat.com> <20170.1336555274@redhat.com> <20120509111958.GA11345@infradead.org> <4FAA5B24.1020306@itwm.fraunhofer.de> <20120509120544.GA17535@infradead.org> <4FAA6230.7040700@itwm.fraunhofer.de> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Christoph Hellwig , David Howells , Dave Chinner , bfields@fieldses.org, smfrench@gmail.com, ben@decadent.org.uk, Trond.Myklebust@netapp.com, roland@hack.frob.com, jra@samba.org, linux-fsdevel@vger.kernel.org, linux-nfs@vger.kernel.org, linux-cifs@vger.kernel.org, samba-technical@lists.samba.org, linux-ext4@vger.kernel.org, linux-api@vger.kernel.org, libc-alpha@sourceware.org To: Andreas Dilger Return-path: Received: from mailgw1.uni-kl.de ([131.246.120.220]:49412 "EHLO mailgw1.uni-kl.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755041Ab2EIONN (ORCPT ); Wed, 9 May 2012 10:13:13 -0400 In-Reply-To: Sender: linux-ext4-owner@vger.kernel.org List-ID: On 05/09/2012 03:51 PM, Andreas Dilger wrote: > On 2012-05-09, at 6:25 AM, Bernd Schubert wrote: >> On 05/09/2012 02:05 PM, Christoph Hellwig wrote: >>> On Wed, May 09, 2012 at 01:55:16PM +0200, Bernd Schubert wrote: >>>> The basic idea of generation numbers is to check if an inode was >>>> recycled, so only if the tuple of inode-number and generation-number >>>> matches we still have the same file. Kernel nfs >>> >>> NFS does not and should not look at the inode generation. Except for a >>> bit of legacy code for the old pre-Linux 2.4 filehandles it looks at the >>> opaque file handle returned and only interpreted by the filesystem. Any >>> userspace NFS server should do the same. >> >> Ok, I didn't look how kernel NFS does it for quite some time already... >> User space NFS only can do it beginning with 2.6.39 - given that user space also needs to support older kernels and other OSs, which might not have open_by_handle, userspace unfortunately cannot entirely rely on that feature. > > But even fewer kernels have sys_statxat() in them (i.e. none), so you can rely on that even less than open_by_handle()... Well, I didn't say that :) In summary, an application needs to try to use the open-by-handle call and if that is not supported, it has to fall back to traditional stat and generation-number-ioctl. And as I said before, open-by-handle very likely removes the requirement for generation numbers in sys_statxat(). Cheers, Bernd