From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756752AbbAZTa4 (ORCPT ); Mon, 26 Jan 2015 14:30:56 -0500 Received: from zeniv.linux.org.uk ([195.92.253.2]:41234 "EHLO ZenIV.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755788AbbAZTax (ORCPT ); Mon, 26 Jan 2015 14:30:53 -0500 Date: Mon, 26 Jan 2015 19:30:49 +0000 From: Al Viro To: Steven Rostedt Cc: linux-kernel@vger.kernel.org, Greg Kroah-Hartman , Ingo Molnar , Andrew Morton Subject: Re: [PATCH 00/16 v3] tracing: Add new file system tracefs Message-ID: <20150126193049.GN29656@ZenIV.linux.org.uk> References: <20150126150913.653681560@goodmis.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150126150913.653681560@goodmis.org> 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 Mon, Jan 26, 2015 at 10:09:13AM -0500, Steven Rostedt wrote: > There has been complaints that tracing is tied too much to debugfs, > as there are systems that would like to perform tracing, but do > not mount debugfs for security reasons. That is because any subsystem > may use debugfs for debugging, and these interfaces are not always > tested for security. > > Creating a new tracefs that the tracing directory will now be attached > to allows system admins the ability to access the tracing directory > without the need to mount debugfs. > > Another advantage is that debugfs does not support the system calls > for mkdir and rmdir. Tracing uses these system calls to create new > instances for sub buffers. This was done by a hack that hijacked the > dentry ops from the "instances" debugfs dentry, and replacing it with > one that could work. > > Instead of using this hack, tracefs can provide a proper interface to > allow the tracing system to have a mkdir and rmdir feature. > > To maintain backward compatibility with older tools that expect that > the tracing directory is mounted with debugfs, the tracing directory > is still created under debugfs and tracefs is automatically mounted > there. > > Finally, a new directory is created when tracefs is enabled called > /sys/kernel/tracing. This will be the new location that system admins > may mount tracefs if they are not using debugfs. You are still fighting an inconvenient API, but now it's not debugfs one - it's your copy thereof. Why not give your instances/ an inode_operations of its own? One with ->mkdir() and ->rmdir(), leaving all other directories as-is. That way you don't need the secondary methods at all. And sure, debugfs_create_dir() grabs ->i_mutex on parent, making you drop that in your ->mkdir() if you want to call it. But now you are not talking to it - just to your own code, where you are free to change the calling conventions, making it caller's responsibility to get that ->i_mutex. The same goes for the rmdir side...