netdev - Re: [PATCH net-next v5] rtnetlink: add new RTM

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Date:	Mon, 18 Apr 2016 21:17:44 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	David Miller <davem@...emloft.net>, Xin Long <lucien.xin@...il.com>
Cc:	roopa@...ulusnetworks.com, netdev@...r.kernel.org,
	jhs@...atatu.com, tgraf@...g.ch, nicolas.dichtel@...nd.com
Subject: Re: [PATCH net-next v5] rtnetlink: add new RTM_GETSTATS message to
 dump link stats

On Mon, 2016-04-18 at 23:41 -0400, David Miller wrote:
> From: Roopa Prabhu <roopa@...ulusnetworks.com>
> Date: Mon, 18 Apr 2016 14:10:19 -0700
> 
> > This patch adds a new RTM_GETSTATS message to query link stats via
> > netlink from the kernel. RTM_NEWLINK also dumps stats today, but
> > RTM_NEWLINK returns a lot more than just stats and is expensive in
> > some cases when frequent polling for stats from userspace is a
> > common operation.
> 
> I'm holding off on this until we sort out the 64-bit netlink
> attribute alignment issue.
> 
> Meanwhile, I'll some kind of a fix into the tree for the
> rtnl_fill_stats() change so that it doesn't cause unaligned
> accesses.

Also it looks like my previous feedback for sctp_get_sctp_info() has
been ignored.

<Quoting http://www.spinics.net/lists/netdev/msg372523.html >

info is not guaranteed to be aligned on 8 bytes.

You need to use put_unaligned()

Check commit ff5d749772018 ("tcp: beware of alignments in
tcp_get_info()") for details.

</quote>