From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Ahern Subject: Re: [PATCH net] net: enable interface alias removal via rtnl Date: Mon, 9 Oct 2017 15:17:53 -0600 Message-ID: <1cccbbaa-455b-66e0-a447-7f7e3b3bb375@gmail.com> References: <20171005101940.28550-1-nicolas.dichtel@6wind.com> <6e1671c7-93d7-0090-54f6-6b36abb8ba89@6wind.com> <3e705d90-9b9a-aa02-e1d9-e3a944953014@6wind.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Cc: netdev@vger.kernel.org, Oliver Hartkopp , Stephen Hemminger To: nicolas.dichtel@6wind.com, Oliver Hartkopp , davem@davemloft.net Return-path: Received: from mail-pf0-f194.google.com ([209.85.192.194]:34519 "EHLO mail-pf0-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755461AbdJIVSA (ORCPT ); Mon, 9 Oct 2017 17:18:00 -0400 Received: by mail-pf0-f194.google.com with SMTP id b85so10148394pfj.1 for ; Mon, 09 Oct 2017 14:18:00 -0700 (PDT) In-Reply-To: <3e705d90-9b9a-aa02-e1d9-e3a944953014@6wind.com> Content-Language: en-US Sender: netdev-owner@vger.kernel.org List-ID: On 10/9/17 9:25 AM, Nicolas Dichtel wrote: > Le 09/10/2017 à 16:02, David Ahern a écrit : >> On 10/9/17 2:23 AM, Nicolas Dichtel wrote: >>> Le 06/10/2017 à 22:10, Oliver Hartkopp a écrit : >>>> >>>> >>>> On 10/06/2017 08:18 PM, David Ahern wrote: >>>>> On 10/5/17 4:19 AM, Nicolas Dichtel wrote: >>>>>> IFLA_IFALIAS is defined as NLA_STRING. It means that the minimal length of >>>>>> the attribute is 1 ("\0"). However, to remove an alias, the attribute >>>>>> length must be 0 (see dev_set_alias()). >>>>> >>>>> why not add a check in dev_set_alias that if len is 1 and the 1 >>>>> character is '\0' it means remove the alias? >>> Because it requires an iproute2 patch. iproute2 doesn't send the '\0'. With the >>> command 'ip link set dummy0 alias ""', the attribute length is 0. >> >> iproute2 needs the feature for 0-len strings or perhaps a 'noalias' option. > iproute2 needs nothing ... > >> >> You can reset the alias using the sysfs file. Given that there is a >> workaround for existing kernels and userspace, upstream can get fixed >> without changing the UAPI. >> > I don't get the point with the UAPI. What will be broken? never mind; I see the error of my ways. > I don't see why allowing an attribute with no data is a problem. > I remember the problem now. I made a patch back in March 2016 that adjusted the policy validation to allow 0-length string. I never sent it and forgot about it until today. You changing ifla_policy to NLA_BINARY is achieving the same thing. I think a comment above the policy line is warranted that clarifies IFLA_IFALIAS is a string but to allow a 0-length string to remove the alias NLA_BINARY is used for policy validation. Comparing the validation done for NLA_STRING vs NLA_BINARY it does change the behavior for 256-character strings.