From mboxrd@z Thu Jan  1 00:00:00 1970
From: Boaz Harrosh <bharrosh@panasas.com>
Subject: Re: [PATCH 27/32] scsi_data_buffer
Date: Thu, 18 Oct 2007 12:21:13 +0200
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To: Matthew Wilcox <matthew@wil.cx>
Cc: Benny Halevy <bhalevy@panasas.com>, James Bottomley <James.Bottomley@SteelEye.com>, Jens Axboe <jens.axboe@oracle.com>, FUJITA Tomonori <tomof@acm.org>, Matthew Dharm <mdharm-scsi@one-eyed-alien.net>, Russell King <rmk@arm.linux.org.uk>, Alan Stern <stern@rowland.harvard.edu>, "David S. Miller" <davem@davemloft.net>, Christoph Hellwig <hch@infradead.org>, linux-scsi <linux-scsi@vger.kernel.org>, Pete Wyckoff <pw@osc.edu>

On Thu, Oct 18 2007 at 10:54 +0200, Matthew Wilcox <matthew@wil.cx> wrote:
> On Thu, Oct 18, 2007 at 10:16:38AM +0200, Boaz Harrosh wrote:
>> Sorry Matthew, my mistake I forgot to send the last [33/33] patch
>> this here should be done on top of that last one.
> 
> Yeah.  I'll rebase the series of 4 patches I just sent on top of it when
> I wake up in the morning.
> 
>> I will grab your tool and play with it. The sglist pointer shuffle
>> is good, and also I know that if you put the scsi_data_buffer
>> at the beginning of scsi_cmnd, than you can fill the holes with small types
>> following the sub-structure. I'll give it a try.
> 
> No, that doesn't work ;-(
> 
> I think a macro to hide the ugliness of my earlier suggestion might fly.
> Something like ...
> 
> #define STRUCT_PACK(a, b, c, d) \
> 	union { a; struct { \
> 		char _packed_ ## __stringify(a) [sizeof(a) - sizeof(c) + sizeof(d)]; \
> 		b; \
> 	}; }
> 
> then we use it like:
> 
> struct scsi_cmnd {
> 	...
> 	STRUCT_PACK(struct scsi_data_buffer sdb, int result,
> 						sizeof(long), sizeof(int));
> }
> 
> Even that's still pretty foul (and i have my grave doubts about using
> stringify in that manner).  It's definitely past my bedtime now ... but
> a hack like that could save us another 8 bytes on x86-64.
> 

You lost me.
What union, please look at patch [33/33]

Boaz