linux-kernel - Re: [PATCH net-next v2] block/drbd: use nla_put_u64

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Date:	Wed, 04 May 2016 10:13:36 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	nicolas.dichtel@...nd.com, netdev@...r.kernel.org,
	philipp.reisner@...bit.com, drbd-dev@...ts.linbit.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next v2] block/drbd: use nla_put_u64_64bit()

On Wed, 2016-05-04 at 12:50 -0400, David Miller wrote:
> From: Eric Dumazet <eric.dumazet@...il.com>
> Date: Wed, 04 May 2016 07:27:06 -0700
> 
> > kernel was fine, and most user land apps were fine as well.
> 
> Userland should really not have to deal with garbage like this.
> 
> And because it quietly works just fine on x86-64, nothing makes
> sure that applications will universally get this right anyways.
> 
> Better to align things properly and magically all of these issues
> simply disappear.

Sure, but in practice we end up consuming 16 bytes (instead of 12) per
u64 attribute, only on some arches. 33 % space overhead.

So maybe some dumps will abort on those arches, while on x86 the size of
skb might be below some magic limit.

I guess this is fine, we do not break ABI in any way.