From mboxrd@z Thu Jan 1 00:00:00 1970 From: ebiederm@xmission.com (Eric W. Biederman) Subject: Re: [PATCH 2/2] ovl: allow distributed fs as lower layer Date: Sat, 06 Jun 2015 20:02:56 -0500 Message-ID: <877frgwcsf.fsf@x220.int.ebiederm.org> References: <1433424586-7771-1-git-send-email-miklos@szeredi.hu> <1433424586-7771-3-git-send-email-miklos@szeredi.hu> <20150605000715.GP7232@ZenIV.linux.org.uk> <20150605150939.GA2174@tucsk> Mime-Version: 1.0 Content-Type: text/plain Return-path: Received: from out03.mta.xmission.com ([166.70.13.233]:56460 "EHLO out03.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752257AbbFGBIF (ORCPT ); Sat, 6 Jun 2015 21:08:05 -0400 In-Reply-To: <20150605150939.GA2174@tucsk> (Miklos Szeredi's message of "Fri, 5 Jun 2015 17:37:29 +0200") Sender: linux-unionfs-owner@vger.kernel.org List-Id: linux-unionfs@vger.kernel.org To: Miklos Szeredi Cc: Al Viro , linux-unionfs@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, sa-dev@rainbow.by, andre.roth@roche.com Miklos Szeredi writes: > On Fri, Jun 05, 2015 at 01:07:15AM +0100, Al Viro wrote: > >> Umm... Cosmetical point is that this >> >> > +static bool ovl_remote(struct dentry *root) >> > +{ >> > + const struct dentry_operations *dop = root->d_op; >> > + >> > + return dop && (dop->d_revalidate || dop->d_weak_revalidate); >> > +} >> >> is better done as >> root->d_flags & (DCACHE_OP_REVALIDATE | DCACHE_OP_WEAK_REVALIDATE) > > Okay. > >> >> More interesting question is whether anything in the system relies on >> existing behaviour that follows ->d_revalidate() returning 0. > > Hmm, d_invalidate() almost always follows ->d_revalidate(). Almost, becuase RCU > lookup can get aborted at that point. We can easily stick d_invalidate() in > there for the non-RCU case. > > Regular lookup also almost always follows ->d_revalidate(). Except if > allocation of new dentry fails. So relying on this would be buggy (which is not > to say nobody does it). > >> Have you tried to mount e.g. procfs as underlying layer and torture it for a >> while? > > I did try now. Nothing bad happened during the test (parallel stat(1) of the > whole overlayed proc tree). > > My laptop froze while trying to write this mail. But it's 8 years old and when > the fan starts to make noises and the weather is hot, it does this sometimes. I > don't think that has anything to do with overlayfs, but will do more > testing... A nasty corner case to be aware of (and I think this is part of what Al was warning about). /proc/sys/net is different depending upon which current->nsproxy->net_ns. Eric