Return-Path: Received: from fieldses.org ([173.255.197.46]:56136 "EHLO fieldses.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751854AbdDNTdj (ORCPT ); Fri, 14 Apr 2017 15:33:39 -0400 Date: Fri, 14 Apr 2017 15:33:38 -0400 From: "J. Bruce Fields" To: Chuck Lever Cc: List Linux RDMA Mailing , Linux NFS Mailing List Subject: Re: [PATCH v3 09/14] svcrdma: Report Write/Reply chunk overruns Message-ID: <20170414193338.GA10208@fieldses.org> References: <20170409163820.15073.43257.stgit@klimt.1015granger.net> <20170409170641.15073.82788.stgit@klimt.1015granger.net> <20170414155634.GC5362@fieldses.org> <20170414175216.GA8290@fieldses.org> <809B3E7B-8991-4358-804F-B2D0101723FF@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <809B3E7B-8991-4358-804F-B2D0101723FF@oracle.com> Sender: linux-nfs-owner@vger.kernel.org List-ID: On Fri, Apr 14, 2017 at 03:07:20PM -0400, Chuck Lever wrote: > > > On Apr 14, 2017, at 1:52 PM, J. Bruce Fields wrote: > > > > On Fri, Apr 14, 2017 at 12:10:03PM -0400, Chuck Lever wrote: > >> > >>> On Apr 14, 2017, at 11:56 AM, J. Bruce Fields wrote: > >>> > >>> On Sun, Apr 09, 2017 at 01:06:41PM -0400, Chuck Lever wrote: > >>>> Observed at Connectathon 2017. > >>>> > >>>> If a client has underestimated the size of a Write or Reply chunk, > >>>> the Linux server writes as much payload data as it can, then it > >>>> recognizes there was a problem and closes the connection without > >>>> sending the transport header. > >>> > >>> Why would the client underestimate? Is this a client-side bug? > >> > >> It can be a bug, and the behavior in this case is that the > >> client retransmits indefinitely and deadlocks the transport, > >> because the client's upper layer never sees a reply. > >> > >> But as you know there are some NFS operations where the client > >> cannot predict in advance how large the reply will be. In > >> particular the upper bound size of an NFSACL GETACL reply or > >> certain NFSv4 GETATTR attributes are not predictable. > > > > Oh, I'd forgotten about those cases. > > > >> These > >> I might categorize as protocol bugs. > >> > >> A client can do its best by posting a very large reply buffer > >> for such operations, but since these situations typically > >> are in practice rare, but NFSv4 GETATTR can be a relatively > >> common operation, clients post a few dozen KB for the reply > >> buffer and call it a day. > >> > >> In these cases (if they should ever fail IRL), returning an > >> error is polite and allows operation of other RPCs on that > >> transport to continue. > > > > Got it, thanks. (I assume this is documented somewhere in the specs?) > > I've written about it in rfc5667bis-09. It's a short document, > review comments welcome. Oh, look, right there in https://tools.ietf.org/html/draft-ietf-nfsv4-rfc5667bis-09#section-2.1 Thanks! And apologies for not keeping up with stuff. --b.