netdev - Re: [PATCH] net, neigh: introduce interval_probe

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Date:   Fri, 20 May 2022 17:56:01 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Yuwei Wang <wangyuweihx@...il.com>
Cc:     davem@...emloft.net, edumazet@...gle.com, daniel@...earbox.net,
        roopa@...dia.com, dsahern@...nel.org, qindi@...ff.weibo.com,
        netdev@...r.kernel.org
Subject: Re: [PATCH] net, neigh: introduce interval_probe_time for periodic
 probe

On Fri, 20 May 2022 05:51:04 +0000 Yuwei Wang wrote:
> commit 7482e3841d52 ("net, neigh: Add NTF_MANAGED flag for managed neighbor entries")
> neighbor entries which with NTF_EXT_MANAGED flags will periodically call neigh_event_send()
> for performing the resolution. and the interval was set to DELAY_PROBE_TIME
> 
> DELAY_PROBE_TIME was configured as the first probe time delay, and it makes sense to set it to `0`.
> 
> when DELAY_PROBE_TIME is `0`, the resolution of neighbor entries with NTF_EXT_MANAGED will
> trap in an infinity recursion.

Recursion or will constantly get re-resolved?

> as commit messages mentioned in the above commit, we should introduce a new option which means resolution interval.
> 
> Signed-off-by: Yuwei Wang <wangyuweihx@...il.com>

> diff --git a/include/uapi/linux/neighbour.h b/include/uapi/linux/neighbour.h
> index 39c565e460c7..5ae538be64b9 100644
> --- a/include/uapi/linux/neighbour.h
> +++ b/include/uapi/linux/neighbour.h
> @@ -143,6 +143,7 @@ enum {
>  	NDTPA_RETRANS_TIME,		/* u64, msecs */
>  	NDTPA_GC_STALETIME,		/* u64, msecs */
>  	NDTPA_DELAY_PROBE_TIME,		/* u64, msecs */
> +	NDTPA_INTERVAL_PROBE_TIME,	/* u64, msecs */
>  	NDTPA_QUEUE_LEN,		/* u32 */
>  	NDTPA_APP_PROBES,		/* u32 */
>  	NDTPA_UCAST_PROBES,		/* u32 */

You can't insert values in the middle of a uAPI enum,
you'll break binary compatibility with older kernels.