From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: linux-nfs-owner@vger.kernel.org Received: from out03.mta.xmission.com ([166.70.13.233]:56713 "EHLO out03.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755833Ab2JIWrw (ORCPT ); Tue, 9 Oct 2012 18:47:52 -0400 From: ebiederm@xmission.com (Eric W. Biederman) To: "J. Bruce Fields" Cc: "Myklebust\, Trond" , Alexander Viro , Stanislav Kinsbursky , "linux-nfs\@vger.kernel.org" , "linux-kernel\@vger.kernel.org" , "devel\@openvz.org" References: <20121008105437.18668.99905.stgit@localhost.localdomain> <20121009193506.GA19680@fieldses.org> <4FA345DA4F4AE44899BD2B03EEEC2FA90901A143@SACEXCMBX04-PRD.hq.netapp.com> <87txu3bdnj.fsf@xmission.com> <20121009223139.GA25826@fieldses.org> Date: Tue, 09 Oct 2012 15:47:42 -0700 In-Reply-To: <20121009223139.GA25826@fieldses.org> (J. Bruce Fields's message of "Tue, 9 Oct 2012 18:31:39 -0400") Message-ID: <87bogb1cvl.fsf@xmission.com> MIME-Version: 1.0 Content-Type: text/plain Subject: Re: [PATCH v3] SUNRPC: set desired file system root before connecting local transports Sender: linux-nfs-owner@vger.kernel.org List-ID: "J. Bruce Fields" writes: > On Tue, Oct 09, 2012 at 01:20:48PM -0700, Eric W. Biederman wrote: >> "Myklebust, Trond" writes: >> >> > On Tue, 2012-10-09 at 15:35 -0400, J. Bruce Fields wrote: >> >> Cc'ing Eric since I seem to recall he suggested doing it this way? >> >> Yes. On second look setting fs->root won't work. We need to change fs. >> The problem is that by default all kernel threads share fs so changing >> fs->root will have non-local consequences. > > Oh, huh. And we can't "unshare" it somehow? I don't fully understand how nfs uses kernel threads and work queues. My general understanding is work queues reuse their kernel threads between different users. So it is mostly a don't pollute your environment thing. If there was a dedicated kernel thread for each environment this would be trivial. What I was suggesting here is changing task->fs instead of task->fs.root. That should just require task_lock(). > Or, previously you suggested: > > - introduce sockaddr_fd that can be applied to AF_UNIX sockets, > and teach unix_bind and unix_connect how to deal with a second > type of sockaddr, AT_FD: > struct sockaddr_fd { short fd_family; short pad; int fd; } > > - introduce sockaddr_unix_at that takes a directory file > descriptor as well as a unix path, and teach unix_bind and > unix_connect to deal with a second sockaddr type, AF_UNIX_AT: > struct sockaddr_unix_at { short family; short pad; int dfd; char path[102]; } > > Any other options? I am still half hoping we don't have to change the userspace API/ABI. There is sanity checking on that path that no one seems interested in to solve this problem. This is a weird issue as we are dealing with both the vfs and the networking stack. Fundamentally we need to change task->fs.root or we need to capitialize on the openat functionality in the kernel, so that we don't create mountains of special cases to support this. I think swapping task->fs instead of task->fs.root is effecitely the same complexity. >> I very much believe we want if at all possible to perform a local >> modification. >> >> Changing fs isn't all that different from what devtmpfs is doing. > > Sorry, I don't know much about devtmpfs, are you suggesting it as a > model? What exactly should we look at? Roughly all I meant was that devtmpsfsd is a kernel thread that runs with an unshared fs struct. Although I admit devtmpfsd is for all practical purposes a userspace daemon that just happens to run in kernel space. Eric