linux-kernel - Re: [PATCH 1/3] 24-bit types: typedef and macros for accessing 3-byte arrays as integers

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Message-ID: <41b516cb0809101851p79f73499vbd10dec4f6bdeccb@mail.gmail.com>
Date:	Wed, 10 Sep 2008 18:51:37 -0700
From:	"Chris Leech" <christopher.leech@...el.com>
To:	"Boaz Harrosh" <bharrosh@...asas.com>
Cc:	"Dave Kleikamp" <shaggy@...ux.vnet.ibm.com>,
	"Christoph Hellwig" <hch@...radead.org>,
	jfs-discussion@...ts.sourceforge.net, linux-kernel@...r.kernel.org,
	linux-scsi@...r.kernel.org, devel@...n-fcoe.org
Subject: Re: [PATCH 1/3] 24-bit types: typedef and macros for accessing 3-byte arrays as integers

On Wed, Sep 10, 2008 at 9:11 AM, Boaz Harrosh <bharrosh@...asas.com> wrote:
> Chris you might want to change the definitions at linux/types.h
> to:
>
> typedef struct { __u8 b[3]; } __be24, __le24 __packed;
>
> With gcc it will not help with the proceeding fields, and the
> containing struct will need it's own "__packed" declaration
> but it will keep it packed with previous fields.

I haven't seen padding added simply because of a nested structure
boundary, but I'm not up on all the ABIs for the different
architectures.  Obviously a containing structure would want to have
the 24-bit type adjacent to an 8-bit type, or have it's own packed
attribute if needed.

It shouldn't hurt, in this case the members shouldn't be expected to
have more than byte alignment anyway, but I can't see how it would
help.

If there's a particular arch that might be a problem I'm happy to look
into it, but I don't want to start throwing packed attributes around
just in case.

Chris
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