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

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Message-ID: <48C80C11.9080103@panasas.com>
Date:	Wed, 10 Sep 2008 21:04:01 +0300
From:	Boaz Harrosh <bharrosh@...asas.com>
To:	Chris Leech <christopher.leech@...el.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
Subject: Re: [Open-FCoE] [PATCH 1/3] 24-bit types: typedef and macros for
 accessing 3-byte arrays as integers

Chris Leech wrote:
> Chris Leech wrote:
>> Dave Kleikamp wrote:
>>> @@ -62,7 +60,7 @@ struct timestruc_t {
>>>   */
>>>  typedef struct {
>>>  	unsigned len:24;
>>> -	unsigned off1:8;
>>> +	u8 off1;
>>>  	u32 off2;
>>>  } lxd_t;
>> Shouldn't len here be changed to a __le24?  I think this just changed
>> the size of lxd_t by a byte.
> 
> Never mind, I see that it's a host order field.  And presently surprised
> to see that gcc combines the 24-bit bitfield with the following u8.
> 
> Chris

It does because these are all bytes. on x86. But this is not guarantied
for all ARCHs and machine-word-sizes. In any way this should be consistent
with the rest of the file.

Please see my other reply about packing of structures. If this is
on-the-wire then there are problems.

Boaz
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