From: ebiederm@xmission.com (Eric W. Biederman) Subject: Re: [RFC][PATCH 2/4] sunrpc: Use utsnamespaces Date: Tue, 06 Jan 2009 15:04:17 -0800 Message-ID: References: <20090106011314.534653345@us.ibm.com> <20090106011314.961946803@us.ibm.com> <20090106200229.GA17031@us.ibm.com> <1231274682.20316.65.camel@heimdal.trondhjem.org> <20090106215831.GE18147@us.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Trond Myklebust , Matt Helsley , Linux Containers , linux-nfs@vger.kernel.org, Linux Kernel Mailing List , "J. Bruce Fields" , Chuck Lever , "Eric W. Biederman" , Linux Containers , Cedric Le Goater To: "Serge E. Hallyn" Return-path: Received: from out02.mta.xmission.com ([166.70.13.232]:45826 "EHLO out02.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751620AbZAFXHt (ORCPT ); Tue, 6 Jan 2009 18:07:49 -0500 In-Reply-To: <20090106215831.GE18147@us.ibm.com> (Serge E. Hallyn's message of "Tue, 6 Jan 2009 15:58:31 -0600") Sender: linux-nfs-owner@vger.kernel.org List-ID: "Serge E. Hallyn" writes: > Quoting Trond Myklebust (trond.myklebust@fys.uio.no): >> On Tue, 2009-01-06 at 14:02 -0600, Serge E. Hallyn wrote: >> > Quoting Matt Helsley (matthltc@us.ibm.com): >> > > We can often specify the UTS namespace to use when starting an RPC client. >> > > However sometimes no UTS namespace is available (specifically during > system >> > > shutdown as the last NFS mount in a container is unmounted) so fall >> > > back to the initial UTS namespace. >> > >> > So what happens if we take this patch and do nothing else? >> > >> > The only potential problem situation will be rpc requests >> > made on behalf of a container in which the last task has >> > exited, right? So let's say a container did an nfs mount >> > and then exits, causing an nfs umount request. >> > >> > That umount request will now be sent with the wrong nodename. >> > Does that actually cause problems, will the server use the >> > nodename to try and determine the client sending the request? >> >> The NFSv2/v3 umount rpc call will be sent by the 'umount' program from >> userspace, not the kernel. The problem here is that because lazy mounts >> exist, the lifetime of the RPC client may be longer than that of the > > Right that was what i was referring to. > >> container. In addition, it may be shared among more than 1 container, >> because superblocks can be shared. > > Good point. And in that case what do we care about (even though > apparently we just might not care at all :) - who did the mount, > or who is using it? > > In fact one thing I noticed in Matt's patch 3 was that he copied > in the nodename verbatim, so a future hostname() by the container > wouldn't be reflected, again not sure if that would matter. > >> One thing you need to be aware of here is that inode dirty data >> writebacks may be initiated by completely different processes than the >> one that dirtied the inode. > > Right, but I *was* thinking that we wanted to associate the nodename > on the rpc calls with the hostname of the mounter, not the actor. Maybe > you'll tell me above that that is bogus. > >> IOW: Aside from being extremely ugly, approaches like [PATCH 4/4] which >> rely on being able to determine the container-specific node name at RPC >> generation time are therefore going to return incorrect values. > > So should we use patch 2/4, plus (as someone - was it you? - suggested) > using a DEFAULT instead of init_utsname()->nodename when > current->utsname() == NULL? Is there any reason to believe that the kernel helper threads will ever have a useful namespace value? I don't think so. That implies to me you want to capture the value at mount time, and to pass it in to the rpc_call creation, and only at very specific well defined points where we interact with user space should we examine current->utsname(). At which point there should be no question of current->utsname() is valid as the user space process is alive. Eric