linux-kernel - Re: [PATCH 5/5]bluetooth:hci_bcsp Fix operation on 'bcsp->msgq

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Message-ID: <4C28E23B.7020406@gmail.com>
Date:	Mon, 28 Jun 2010 10:56:11 -0700
From:	"Justin P. Mattock" <justinmattock@...il.com>
To:	David Howells <dhowells@...hat.com>
CC:	"Gustavo F. Padovan" <gustavo@...ovan.org>,
	linux-kernel@...r.kernel.org, sds@...ho.nsa.gov, lenb@...nel.org,
	linux-bluetooth@...r.kernel.org
Subject: Re: [PATCH 5/5]bluetooth:hci_bcsp Fix operation on 'bcsp->msgq_txseq'
 may be undefined

On 06/28/2010 05:52 AM, David Howells wrote:
> Justin P. Mattock<justinmattock@...il.com>  wrote:
>
>> -		BT_DBG("Sending packet with seqno %u", bcsp->msgq_txseq);
>> -		bcsp->msgq_txseq = ++(bcsp->msgq_txseq)&  0x07;
>> +		BT_DBG("Sending packet with seqno %u", bcsp->msgq_txseq | ret);
>> +		ret = ++(bcsp->msgq_txseq)&  0x07;
>
> I don't know what you're trying to do here, but you seem to be trying to send
> the computed value back in time.
>

I was under the impression that hdr[0] |= 0x80 + bcsp->msgq_txseq;
is computing a value for BT_DBG then ret = ++(bcsp->msgq_txseq)&  0x07
computes a value as well i.e.

BT_DBG("Sending packet with seqno %u", hdr[0] | ret);

> The problem is that the compiler is confused about why a '++' operator makes
> any sense here.  It doesn't.  It should be a '+ 1' instead.  I think what you
> want is:
>
> 	-	bcsp->msgq_txseq = ++(bcsp->msgq_txseq)&  0x07;
> 	+	bcsp->msgq_txseq = (bcsp->msgq_txseq + 1)&  0x07;
>
> David
>

yeah I did play around with the ++ and noticed the compiler would be 
satisfied if the ++ was not there, but didn't think to just add a + 1

Justin P. Mattock
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