linux-kernel - Re: [RFC patch] sctp: sctp_generate_fwdtsn: Initialize sctp_fwdtsn

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Date:	Mon, 6 Jul 2015 09:43:49 -0400
From:	Neil Horman <nhorman@...driver.com>
To:	Joe Perches <joe@...ches.com>
Cc:	Vlad Yasevich <vyasevich@...il.com>,
	"David S. Miller" <davem@...emloft.net>,
	linux-sctp@...r.kernel.org, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC patch] sctp: sctp_generate_fwdtsn: Initialize
 sctp_fwdtsn_skip array, neatening

On Fri, Jul 03, 2015 at 09:41:41AM -0700, Joe Perches wrote:
> On Fri, 2015-07-03 at 07:51 -0400, Neil Horman wrote:
> > On Thu, Jul 02, 2015 at 02:54:56PM -0700, Joe Perches wrote:
> > > It's not clear to me that the sctp_fwdtsn_skip array is
> > > always initialized when used.
> > > 
> > > It is appropriate to initialize the array to 0?
> > > 
> > > This patch initializes the array too 0 and moves the
> > > local variables into the blocks where used.
> > > 
> > > It also does some miscellaneous neatening by using
> > > continue; and unindenting the following block and
> > > using ARRAY_SIZE rather than 10 to decouple the
> > > array declaration size from a constant.
> > > ---
> > We don't set ftsn_skip_arr to a known value because we limit the amount of
> > elements that get read from it prior to those elements being set.  That is to
> > say, in our first use (the call to sctp_get_skip_pos), we pass the uninitialized
> > array, and the nskips value, which is initalized to 0.  Looking at the
> > definition of sctp_get_skip_pos, the for loop there becomes a nop, meaning the
> > uninitalized array is irrelevant, as we never visit any of its elements.
> > element zero is returned, and thats what the for_each loop in
> > sctp_generate_fwdtsn sets in that element of the array.  On the next iteration
> > of the for_each loop, we call sctp_get_skip_pos with nskips = 1, so only the
> > first element is visited, whcih was set by the previous loop iteration.
> 
> Alright.
> 
> I might have chosen a while loop to limit the # of
> returns but it likely compiles to the same code.
> 
> static inline int sctp_get_skip_pos(struct sctp_fwdtsn_skip *skiplist,
> 				    int nskips, __be16 stream)
> {
> 	int i;
> 
> 	for (i = 0; i < nskips; i++) {
> 		if (skiplist[i].stream == stream)
> 			return i;
> 	}
> 	return i;
> }
> 
> to:
> 
> {
> 	int i = 0;
> 
> 	while (i < nskips && skiplist[i].stream != stream)
> 		i++;
> 
> 	return i;
> }
> 
> > The rest of the cleanups look ok I think.  Can you tell me what you did to test
> > it?
> 
> Just code inspection.

I'd like something more than that for this amount of code change.  at least run
some lksctp tests to exercise the gap ack code.
Neil

> 
> 
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