From owner-freebsd-hackers  Sat Sep 15 13:45:33 2001
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To: hackers@FreeBSD.ORG
Subject: Re: Driver structures & alignment 
Cc: Yar Tikhiy <yar@FreeBSD.ORG>, Mike Smith <msmith@FreeBSD.ORG>,
	msmith@mass.dis.org
In-reply-to: Your message of "Sat, 15 Sep 2001 12:26:15 PDT."
		<20010915122615.A72222@dragon.nuxi.com> 
References: <20010915122615.A72222@dragon.nuxi.com>  <20010915110337.B53569@dragon.nuxi.com> <yar@freebsd.org> <200109132309.f8DN9vX03967@mass.dis.org> <20010914122344.A38530@snark.rinet.ru> <20010915110337.B53569@dragon.nuxi.com> <200109151813.f8FIDwW02011@harmony.village.org> 
Date: Sat, 15 Sep 2001 14:44:11 -0600
From: Warner Losh <imp@harmony.village.org>
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In message <20010915122615.A72222@dragon.nuxi.com> "David O'Brien" writes:
: On Sat, Sep 15, 2001 at 12:13:58PM -0600, Warner Losh wrote:
: > In message <20010915110337.B53569@dragon.nuxi.com> "David O'Brien" writes:
: > : It is best to order this from largest to smallest size if you are worried
: > : about alignment holes, etc.
: > : 
: > :  	int64_t d; /* 8-byte boundary */
: > :  	int32_t c; /* 4-byte boundary */
: > :  	int32_t f; /* 4-byte boundary */
: > :  	int16_t	a;
: > :  	int16_t b;
: > :  	int8_t  e[4];
: > 
: > unfortunately, there are many device structures that are passed around 
: > via DMA and hte like that don't let you do this...
: 
: How come?  The struct represents some [semi-]physical organization?

Because the hardware designer may have done silly things.  These are
hardware data structures.

Warner

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