From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755347AbbAYU1i (ORCPT ); Sun, 25 Jan 2015 15:27:38 -0500 Received: from zeniv.linux.org.uk ([195.92.253.2]:37533 "EHLO ZenIV.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752107AbbAYU1f (ORCPT ); Sun, 25 Jan 2015 15:27:35 -0500 Date: Sun, 25 Jan 2015 20:27:29 +0000 From: Al Viro To: Steven Rostedt Cc: Greg Kroah-Hartman , linux-kernel@vger.kernel.org, Ingo Molnar , Andrew Morton Subject: Re: [PATCH 3/5 v2] tracing: Automatically mount tracefs on debugfs/tracing Message-ID: <20150125202729.GI29656@ZenIV.linux.org.uk> References: <20150123155525.795129339@goodmis.org> <20150123162414.580817092@goodmis.org> <20150124030041.GB5009@kroah.com> <20150124063330.2c986ea2@grimm.local.home> <20150125132206.GA16249@kroah.com> <20150125143830.760c448a@gandalf.local.home> <20150125195932.GH29656@ZenIV.linux.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150125195932.GH29656@ZenIV.linux.org.uk> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Jan 25, 2015 at 07:59:32PM +0000, Al Viro wrote: > On Sun, Jan 25, 2015 at 02:38:30PM -0500, Steven Rostedt wrote: > > On Sun, 25 Jan 2015 21:22:07 +0800 > > Greg Kroah-Hartman wrote: > > > > > > > If we could do it in a non-racy way, that would be good, otherwise I > > > don't see us being able to even take this patch :( > > > > Is it still racy even if it's only done at boot up? This path only gets > > hit the first time it is called. "if (tr->flags &TRACE_ARRAY_FL_GLOBAL)" > > is the top level tracing directory ("tracing") and is only called > > during boot up (fs_initcall) and never hit again. I could even make > > this called directly by that code so we could label it "__init" to make > > sure that it is to be never hit. Or is this racy even when done by > > fs_initcall? > > > > Waiting for Al to comment on this, because, I can't add this feature > > until debugfs/tracing still containing the tracing information, > > otherwise it will break all the tools that interact with the tracing > > infrastructure, and we all know how happy Linus feels about such > > changes. > > Actually, I'm almost done massaging that sucker into adding > debugfs_create_automount(). The only remaining question is what arguments > do we put it; for now I'm giving it dentry_operations + data (to go into > inode->i_private), but it might be better to give it a pointer just to > d_automount() callback + data for it... Turns out that it is better that way (and less prone to abuse). See vfs.git#debugfs_automount; some massage on top of 3.19-rc5, the payoff is in the last commit. For your code it's a matter of replacing struct path *path with void *unused in trace_automount() and just calling debugfs_create_automount("tracing", NULL, trace_automount, NULL); to create the sucker. That's it - no games with ->d_op, etc.