linux-kernel - Re: [PATCH net-next 9/9] taskstats: use the libnl API to align nlattr on 64-bit

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Date:	Wed, 27 Apr 2016 22:29:22 +1000
From:	Balbir Singh <bsingharora@...il.com>
To:	nicolas.dichtel@...nd.com, netdev@...r.kernel.org
Cc:	davem@...emloft.net, linux-kernel@...r.kernel.org,
	linux-wpan@...r.kernel.org, aar@...gutronix.de,
	pablo@...filter.org, kaber@...sh.net, kadlec@...ckhole.kfki.hu,
	pshelar@...ira.com, kuznet@....inr.ac.ru, jmorris@...ei.org,
	yoshfuji@...ux-ipv6.org, netfilter-devel@...r.kernel.org,
	dev@...nvswitch.org, steffen.klassert@...unet.com,
	herbert@...dor.apana.org.au
Subject: Re: [PATCH net-next 9/9] taskstats: use the libnl API to align nlattr
 on 64-bit



On 27/04/16 17:29, Nicolas Dichtel wrote:
> Le 27/04/2016 03:14, Balbir Singh a écrit :
>>
>>
>> On 23/04/16 01:31, Nicolas Dichtel wrote:
>>> Goal of this patch is to use the new libnl API to align netlink attribute
>>> when needed.
>>> The layout of the netlink message will be a bit different after the patch,
>>> because the padattr (TASKSTATS_TYPE_STATS) will be inside the nested
>>> attribute instead of before it.
>>>
>>> Signed-off-by: Nicolas Dichtel <nicolas.dichtel@...nd.com>
>>
>> The layout will change/break user space -- I've not tested the patch though..
> Sigh.
> 
> I quote David:
> "All userspace components using netlink should always ignore attributes
> they do not recognize in dumps.
> 
> This is one of the most basic principles of netlink"
> 
> Do you have some pointers so I can made some tests?
> 

Please try

https://www.kernel.org/doc/Documentation/accounting/getdelays.c

iotop uses it as well. My concern is ABI breakage of user space.

Balbir Singh