netdev - Re: [PATCH net] net: enable interface alias removal via rtnl

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Message-ID: <ffd17810-8d65-04f5-6841-98c74201780c@gmail.com>
Date:   Mon, 9 Oct 2017 08:02:38 -0600
From:   David Ahern <dsahern@...il.com>
To:     nicolas.dichtel@...nd.com,
        Oliver Hartkopp <socketcan@...tkopp.net>, davem@...emloft.net
Cc:     netdev@...r.kernel.org, Oliver Hartkopp <oliver@...tkopp.net>,
        Stephen Hemminger <stephen@...workplumber.org>
Subject: Re: [PATCH net] net: enable interface alias removal via rtnl

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.

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.

> A kernel patch is probably enough for this problem. Updating iproute2 on old
> distributions is not always easy.

Can't say I have ever heard someone suggest that a kernel is easier to
change than userspace.