netdev - Re: [patch] svcrdma: endian bug in send_write

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Message-ID: <4F0F3380.4000406@opengridcomputing.com>
Date:	Thu, 12 Jan 2012 13:24:48 -0600
From:	Tom Tucker <tom@...ngridcomputing.com>
To:	Trond Myklebust <Trond.Myklebust@...app.com>
CC:	"J. Bruce Fields" <bfields@...ldses.org>,
	Dan Carpenter <dan.carpenter@...cle.com>,
	"David S. Miller" <davem@...emloft.net>, linux-nfs@...r.kernel.org,
	netdev@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: Re: [patch] svcrdma: endian bug in send_write_chunks()

On 1/12/12 1:15 PM, Trond Myklebust wrote:
> On Thu, 2012-01-12 at 11:21 -0500, J. Bruce Fields wrote:
>> On Thu, Jan 12, 2012 at 09:47:22AM +0300, Dan Carpenter wrote:
>>> Sparse complains because arg_ch->rs_length is declared as network
>>> endian but we're treating it as CPU endian.
>> This looks like it would actually change behavior on a little endian
>> architecture, so how did this work before?
>>
>> > From some quick grepping, I see assignments both of the form
>>
>> 	...rs_length = ntohl(...)
>>
>> and
>>
>> 	...rs_length = htonl(...)
>>
>> but only see one declaration for a field named rs_length.
>>
>> So my best guess would be that the code is ugly but working as is, and
>> needs cleanup by someone who knows how this field was intended to be
>> used.
> It looks to me as if rs_handle and rs_offset are being similarly abused.
> Basically, we need a serious clean up in svc_rdma_marshall.c to separate
> out those variables that are in XDR-encoded form and those that are not.
>
The abuse is taking place because the marshal/unmarshall is being done 
in-place and it seemed wasteful at the time to add a chunk of memory to 
preserve the aesthetic. A union would 'work', but you still wouldn't 
'know' whether the data was NBO or not by where it was -- which seems like 
the intent of the __beXX in the first place.

Tom

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