netdev - RE: [PATCH 2/9] ocrdma: Driver for Emulex OneConnect RDMA adapter

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Message-ID: <88B766C272F2C64B944B21AD078333151C964A68E3@EXMAIL.ad.emulex.com>
Date:	Fri, 23 Mar 2012 12:16:52 -0700
From:	<Parav.Pandit@...lex.Com>
To:	<jgunthorpe@...idianresearch.com>
CC:	<David.Laight@...LAB.COM>, <roland@...estorage.com>,
	<linux-rdma@...r.kernel.org>, <netdev@...r.kernel.org>
Subject: RE: [PATCH 2/9] ocrdma: Driver for Emulex OneConnect RDMA adapter

Got it. You did mention about typedef in email chain, but I understood as different way to achieve same.

I reviewed my code and found that most of the fields between driver-adapter doesn't need attribute.
So far (a) removing packed and (b) BUILD_BUG_ON looks sufficient for current set of structures. Initial test suffice the need.

Thanks.
Parav

> -----Original Message-----
> From: Jason Gunthorpe [mailto:jgunthorpe@...idianresearch.com]
> Sent: Friday, March 23, 2012 10:24 PM
> To: Pandit, Parav
> Cc: David.Laight@...LAB.COM; roland@...estorage.com; linux-
> rdma@...r.kernel.org; netdev@...r.kernel.org
> Subject: Re: [PATCH 2/9] ocrdma: Driver for Emulex OneConnect RDMA
> adapter
> 
> On Fri, Mar 23, 2012 at 07:03:37AM -0700, Parav.Pandit@...lex.Com wrote:
> 
> > > David is saying you will get a 12 byte struct and fieldb will be
> > > unaligned. Since
> > > 12 is aligned to 4 no padding is added.
> >
> > So I decided to experiment above example before implementing in
> > driver. However I find structure of 16 bytes (instead of 12) with
> > padding after fielda in below example.  Am I missing some compiler
> > option or syntax error in attribute? Sorry to ask this silly question.
> > I tried __attribute__((__aligned__(4))); too based on usage in other
> > kernel code.
> 
> I got the syntax wrong for that specific case (it is a little unintuitive.. IMHO,
> capping the alignment of a container should cap the alignment of all
> members, otherwise it is nonsense!):
> 
> typedef uint64_t u64_unaligned_8 __attribute__((__aligned__(4)));
> 
> struct foo {
>         uint32_t fielda;
>         u64_unaligned_8 fieldb;
> };
> 
> struct foo2 {
>         uint32_t fielda;
>         uint64_t fieldb;
> };
> 
> int main(int argc,const char *argv[])
> {
> 	printf("sizeof(foo) = %zu, fieldb = %zu\n",sizeof(struct foo),
> 	       offsetof(struct foo,fieldb));
> 	printf("sizeof(foo2) = %zu, fieldb = %zu\n",sizeof(struct foo2),
> 	       offsetof(struct foo2,fieldb));
> 	return 0;
> }
> 
> sizeof(foo) = 12, fieldb = 4
> sizeof(foo2) = 16, fieldb = 8
> 
> gcc version 4.6.1 (Ubuntu/Linaro 4.6.1-9ubuntu3)
> 
> Jason
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