netdev - Re: [PATCH net-next 3/8] fs/quota: use nla_put_u64

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Date:	Tue, 26 Apr 2016 12:24:01 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	jack@...e.cz
Cc:	nicolas.dichtel@...nd.com, netdev@...r.kernel.org,
	sd@...asysnail.net, johannes@...solutions.net,
	kvalo@...eaurora.org, linux-wireless@...r.kernel.org,
	jack@...e.com, linux-kernel@...r.kernel.org, pshelar@...ira.com,
	dev@...nvswitch.org, jhs@...atatu.com, philipp.reisner@...bit.com,
	lars.ellenberg@...bit.com, drbd-dev@...ts.linbit.com
Subject: Re: [PATCH net-next 3/8] fs/quota: use nla_put_u64_64bit()

From: Jan Kara <jack@...e.cz>
Date: Tue, 26 Apr 2016 13:08:48 +0200

> On Tue 26-04-16 10:06:13, Nicolas Dichtel wrote:
>> Signed-off-by: Nicolas Dichtel <nicolas.dichtel@...nd.com>
> 
> OK, so I somewhat miss a description of what will this do to the netlink
> message so that I can judge whether the change is fine for the userspace
> counterpart parsing these messages. AFAIU this changes the message format
> by adding a QUOTA_NL_A_PAD field before each 64-bit field which needs an
> alignment, am I guessing right? Thus when the userspace counterpart uses
> genlmsg_parse() it should just silently ignore these attributes if I read
> the documentation right. Did I understand this correctly?

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.