netdev - Re: [PATCH] bonding,llc: Fix structure sizeof incompatibility for some PDUs

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Date:	Thu, 12 May 2011 15:33:36 +0100
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	Vitalii Demianets <vitas@...factor.kiev.ua>
Cc:	Jay Vosburgh <fubar@...ibm.com>,
	Andy Gospodarek <andy@...yhouse.net>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	netdev@...r.kernel.org, bonding-devel@...ts.sourceforge.net
Subject: Re: [PATCH] bonding,llc: Fix structure sizeof incompatibility for
 some PDUs

On Thu, 2011-05-12 at 15:57 +0300, Vitalii Demianets wrote:
> With some combinations of arch/compiler the sizeof operator on structure 
> returns value greater than expected.

Yes, some architecture ABIs set a minimum alignment for structures so
they can have greater alignment than any of their members.

> In cases when the structure is used for 
> mapping PDU fields it may lead to unexpected results (e.g. holes and 
> alignment problems in skb data). Attribute "packed" prevents this undesired 
> behavior.
[...]

The '__packed' macro is preferred.

Ben.

-- 
Ben Hutchings, Senior Software Engineer, Solarflare
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

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