Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753482Ab2FEW2u (ORCPT ); Tue, 5 Jun 2012 18:28:50 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:35302 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751187Ab2FEW2r (ORCPT ); Tue, 5 Jun 2012 18:28:47 -0400 Date: Tue, 5 Jun 2012 15:28:45 -0700 From: Andrew Morton To: Wanpeng Li Cc: Fengguang Wu , Rob Landley , Alexander Viro , "Eric W. Biederman" , Lucas De Marchi , "David S. Miller" , Jan Kara , Mel Gorman , Minchan Kim , David Howells , James Morris , Ingo Molnar , Michel Lespinasse , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, Gavin Shan , Wanpeng Li Subject: Re: [PATCH v2] remove no longer use of pdflush interface Message-Id: <20120605152845.8b633881.akpm@linux-foundation.org> In-Reply-To: <1338888372-3555-1-git-send-email-liwp.linux@gmail.com> References: <1338888372-3555-1-git-send-email-liwp.linux@gmail.com> X-Mailer: Sylpheed 3.0.2 (GTK+ 2.20.1; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2602 Lines: 78 On Tue, 5 Jun 2012 17:26:11 +0800 Wanpeng Li wrote: > From: Wanpeng Li > > ------------------ > > Change in v2: > > * add printk warning > * add description in Documentation > This is not a changelog. The patch should be accompanied by text explaining the reasons for the removal, the back-compatibility issues, how they were addressed, etc. I do agree with the intent of the patch and the creation of proc_deprecated() seems a good idea - something we can use in the future. > --- a/kernel/sysctl.c > +++ b/kernel/sysctl.c > @@ -1095,11 +1095,9 @@ static struct ctl_table vm_table[] = { > .extra1 = &zero, > }, > { > - .procname = "nr_pdflush_threads", > - .data = &nr_pdflush_threads, > - .maxlen = sizeof nr_pdflush_threads, > - .mode = 0444 /* read-only*/, > - .proc_handler = proc_dointvec, > + .procname = "nr_pdflush_threads", > + .mode = 0444 /* read-only */, > + .proc_handler = proc_deprecated, > }, > { > .procname = "swappiness", > @@ -2505,6 +2503,15 @@ int proc_doulongvec_ms_jiffies_minmax(struct ctl_table *table, int write, > > #endif /* CONFIG_PROC_SYSCTL */ > > +/* notice associated proc deprecated */ > +int proc_deprecated(struct ctl_table *table, int write, > + void __user *buffer, size_t *lenp, loff_t *ppos) > +{ > + printk(KERN_WARNING "%s exported in /proc is deprecated\n", > + table->procname); > + return -ENOSYS; > +} I see a couple of things here. Firstly, I'd change the text from "deprecated" to "is scheduled for removal". Which implies that the function should be called proc_obsolete(). Secondly, this code will permit unprivileged users to flood the logs, by repeatedly reading /proc/sys/vm/nr_pdflush_threads. We try to avoid this, as it is a form of denial-of-service attack. This is a bit hard to fix. The typical way of addressing this is to use printk_once(), so the message only appears once per boot. But that doesn't work for a generic function - we'd need to add one bit of state to the ctl_table to do this. We can of course do that, but it's not obvious that it's _worth_ doing that just for handling obsolete entries. So perhaps the solution is to give up on the generic proc_obsolete() idea, and just add a handler specifically for nr_pdflush_threads, whcih uses printk_once(). -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/