From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Morton Subject: Re: [PATCH v2 1/1] eventfd: implementation of EFD_MASK flag Date: Thu, 14 Feb 2013 21:24:11 -0800 Message-ID: <20130214212411.55788ec1.akpm@linux-foundation.org> References: <1360311077-14474-1-git-send-email-sustrik@250bpm.com> <20130214145430.04f8750c.akpm@linux-foundation.org> <511DAEA3.4080201@250bpm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Cc: Alexander Viro , Sha Zhengju , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, netdev@vger.kernel.org, Michael Kerrisk , Davide Libenzi , Andy Lutomirski , Eric Wong To: Martin Sustrik Return-path: In-Reply-To: <511DAEA3.4080201@250bpm.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On Fri, 15 Feb 2013 04:42:27 +0100 Martin Sustrik wrote: > > This is a non-back-compatible userspace interface change. A procfs > > file which previously displayed > > > > eventfd-count: nnnn > > > > can now also display > > > > eventfd-mask: nnnn > > > > So existing userspace could misbehave. > > > > Please fully describe the proposed interface change in the changelog. > > That description should include the full pathname of the procfs file > > and example before-and-after output and a discussion of whether and why > > the risk to existing userspace is acceptable. > > I am not sure what the policy is here. Is not printing out the state of > the object acceptable way to maintain backward compatibility? If not so, > does new type of object require new procfs file, which, AFAIU, is the > only way to retain full backward compatibility? Adding a new file is the only way I can think of to preserve the API. But from Andy's comment is sounds like we don't have to worry a lot about back-compatibility.