netdev - Re: pull-request: can-next 2017-02-06,pull-request: can-next 2017-02-06

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Message-ID: <809cdb71-a29c-f952-0cab-ff643b4906f0@pengutronix.de>
Date:   Mon, 6 Feb 2017 17:43:43 +0100
From:   Marc Kleine-Budde <mkl@...gutronix.de>
To:     David Miller <davem@...emloft.net>
Cc:     netdev@...r.kernel.org, kernel@...gutronix.de,
        linux-can@...r.kernel.org
Subject: Re: pull-request: can-next 2017-02-06,pull-request: can-next
 2017-02-06

On 02/06/2017 05:12 PM, David Miller wrote:
> From: Marc Kleine-Budde <mkl@...gutronix.de>
> Date: Mon, 6 Feb 2017 15:50:48 +0100
> 
>> this is a pull request of 16 patches for net-next/master.
>>
>> The first two patches by David Jander and me add the rx-offload
>> framework for CAN devices to the kernel. The remaining 14 patches
>> convert the flexcan driver to make use of it.
> 
> Pulled, but I wonder if your comparisons does the right thing when the
> counters overflow.
> 
> I think you need to do the same thing we do for TCP sequence number
> comparisons and code it like:
> 
> static inline bool before(__u32 seq1, __u32 seq2)
> {
>         return (__s32)(seq1-seq2) < 0;
> }

Yes, I think it's basically the same as the TCP sequence number code,
but obviously less readable.

> static int can_rx_offload_compare(struct sk_buff *a, struct sk_buff *b)
> {
> 	const struct can_rx_offload_cb *cb_a, *cb_b;
> 
> 	cb_a = can_rx_offload_get_cb(a);
> 	cb_b = can_rx_offload_get_cb(b);
> 
> 	/* Substract two u32 and return result as int, to keep
> 	 * difference steady around the u32 overflow.
> 	 */
> 	return cb_b->timestamp - cb_a->timestamp;
> }

This does the "(__s32)(seq1-seq2)"

> 	skb_queue_reverse_walk(head, pos) {
> 		const struct can_rx_offload_cb *cb_pos, *cb_new;
> 
> 		cb_pos = can_rx_offload_get_cb(pos);
> 		cb_new = can_rx_offload_get_cb(new);
> 
> 		netdev_dbg(new->dev,
> 			   "%s: pos=0x%08x, new=0x%08x, diff=%10d, queue_len=%d\n",
> 			   __func__,
> 			   cb_pos->timestamp, cb_new->timestamp,
> 			   cb_new->timestamp - cb_pos->timestamp,
> 			   skb_queue_len(head));
> 
> 		if (compare(pos, new) < 0)

And here the "return ... < 0;"

> 			continue;
> 		insert = pos;
> 		break;
> 	}

Marc

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