On 02/06/2017 05:12 PM, David Miller wrote:
> From: Marc Kleine-Budde <m...@pengutronix.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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