netdev - Re: [PATCH] Fix ARM BUILD_BUG_ON() errors with batman-adv

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Message-Id: <20131202.133838.1257454198436895412.davem@davemloft.net>
Date:	Mon, 02 Dec 2013 13:38:38 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	sw@...onwunderlich.de
Cc:	linux@....linux.org.uk, mareklindner@...mailbox.ch,
	antonio@...hcoding.com, b.a.t.m.a.n@...ts.open-mesh.org,
	netdev@...r.kernel.org
Subject: Re: [PATCH] Fix ARM BUILD_BUG_ON() errors with batman-adv

From: Simon Wunderlich <sw@...onwunderlich.de>
Date: Mon, 2 Dec 2013 18:58:47 +0100

> Therefore I'd suggest to pick Russels patch, I can send a fix for 
> batadv_interface_rx() later, too.

You are ignoring the downside of Russel's patch which is that it
negatively impacts many architectures, in that now the compiler
can make no assumptions as to the alignment of a structure marked
with "packed" and therefore, for example, a 32-bit load will
be done with 4 byte loads, shifts, and masking.

Please just 4 byte align your structures.  I can't believe that
you cannot make this work cleanly.

Why can't you just include that fourth final byte in the batadv_header
structure and have the sub-header types just interpret it differently
or ignore it?

This is getting frustrating, I seemed clear to me that the non-packed
suggestions given to you so far were both reasonable and easy to
implement.
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