netdev - Re: [PATCH 3/9] ocrdma: Driver for Emulex OneConnect RDMA adapter

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Date:	Wed, 21 Mar 2012 14:54:26 -0600
From:	Jason Gunthorpe <jgunthorpe@...idianresearch.com>
To:	Roland Dreier <roland@...estorage.com>
Cc:	Parav.Pandit@...lex.com, linux-rdma@...r.kernel.org,
	netdev@...r.kernel.org
Subject: Re: [PATCH 3/9] ocrdma: Driver for Emulex OneConnect RDMA adapter

On Wed, Mar 21, 2012 at 12:33:00PM -0700, Roland Dreier wrote:
> On Wed, Mar 21, 2012 at 12:04 PM,  <Parav.Pandit@...lex.com> wrote:
> >> > +/* mailbox cmd response */
> >> > +struct ocrdma_mbx_rsp {
> >> > + ? ? ? u32 subsys_op;
> >> > + ? ? ? u32 status;
> >> > + ? ? ? u32 rsp_len;
> >> > + ? ? ? u32 add_rsp_len;
> >> > +} __packed;
> 
> >> ...similar comments about only using __packed where you really need it...
> 
> > This pack is required as it is shared with hardware and need to be
> > of 16 bytes for 32 and 64 bit architecture. Do not wanted to take
> > risk of different compiler versions. So keeping it packed.
> 
> I really think if you can't trust your compiler to lay this
> structure out properly, you have a lot of bigger problems.  But
> whatever, it's not a big deal.

Doesn't packed penalize all access to the structure on some
architectures, eg sparc?

A static assert is a better choice than packed...

BUILD_BUG_ON(sizeof(ocrdma_mbx_rsp) != 16);

Jason
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