From owner-freebsd-fs Thu Feb 22 19:27:31 2001 Delivered-To: freebsd-fs@freebsd.org Received: from phoenix.volant.org (dickson.phoenix.volant.org [205.179.79.193]) by hub.freebsd.org (Postfix) with ESMTP id 8AC2537B491 for ; Thu, 22 Feb 2001 19:27:26 -0800 (PST) (envelope-from patl@Phoenix.Volant.ORG) Received: from asimov.phoenix.volant.org ([205.179.79.65]) by phoenix.volant.org with esmtp (Exim 1.92 #8) id 14W8tB-0002Qi-00; Thu, 22 Feb 2001 19:27:25 -0800 Received: from localhost (localhost [127.0.0.1]) by asimov.phoenix.volant.org (8.9.3+Sun/8.9.3) with SMTP id TAA11841; Thu, 22 Feb 2001 19:26:42 -0800 (PST) From: patl@Phoenix.Volant.ORG Date: Thu, 22 Feb 2001 19:26:42 -0800 (PST) Reply-To: patl@Phoenix.Volant.ORG Subject: Re: Status of nullfs To: Peter Wemm Cc: tlambert@primenet.com, freebsd-fs@FreeBSD.ORG In-Reply-To: <200102230242.f1N2gUf43386@mobile.wemm.org> Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; CHARSET=US-ASCII Sender: owner-freebsd-fs@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.org On 22-Feb-01 at 18:42, Peter Wemm (peter@netplex.com.au) wrote: > > Any mmap'ed writes will fail due to cache coherency problems. If > > the system isn't quiescent long enough to flush everything out > > before an unmount, you can panic. If you have exposed the NULL > > mount , e.g. by mounting an FS on /usr, and then nullfs mounting > > it to /null_usr, then modifications to the /usr FS will not > > result in coherency notification, and files will become corrupt, > > if accessed both ways. Paging from executables can cause problems > > for multiple copies of executables, if statically initialized data > > is modified (copy on write) due to the way backing page handling > > is limited. > > > > All of these derive from the fact that the vnode in the upper > > layer (nullfs) and the vnode in the lower layer (ffs or whatever) > > have seperate vm_object_t's, even though the data contents of the > > file are supposed to be treated as identical for both. > > Terry, please check your facts. This has been recently fixed. See the > VOP_GETVOBJECT() stuff. The trick though is to get it MFC'ed into > 4.x... In Terry's support, I -was- specificly asking about -STABLE. > > There are a number of patches to manually enforce coherency; as > > far as I know, they don't deal with the pager path, and, since > > the coherency is explicit, the /usr vs. /null_usr problem is > > not resolved. Check the list archives to obtain the patches. > > nullfs is fully functional in -current. Backporting the changes should > be easy. Hmm. Easy for someone familiar with the kernel internals; or easy for someone with 30 years of systems level software engineering experience but -no- unix kernel experience? (If the later, I may see if I can free up the cycles to do it. If the former, I doubt that I'll get enough cycles to climb that specific learning curve before other priorities intervene.) -Pat To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-fs" in the body of the message