netdev - Re: [Patch net-next v3 3/3] net_sched: implement ->change_tx_queue_len() for pfifo

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Date:   Fri, 26 Jan 2018 11:57:59 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Cong Wang <xiyou.wangcong@...il.com>, netdev@...r.kernel.org
Cc:     john.fastabend@...il.com, "Michael S. Tsirkin" <mst@...hat.com>
Subject: Re: [Patch net-next v3 3/3] net_sched: implement
 ->change_tx_queue_len() for pfifo_fast



On 2018年01月26日 10:26, Cong Wang wrote:
> pfifo_fast used to drop based on qdisc_dev(qdisc)->tx_queue_len,
> so we have to resize skb array when we change tx_queue_len.
>
> Other qdiscs which read tx_queue_len are fine because they
> all save it to sch->limit or somewhere else in qdisc during init.
> They don't have to implement this, it is nicer if they do so
> that users don't have to re-configure qdisc after changing
> tx_queue_len.
>
> Cc: John Fastabend <john.fastabend@...il.com>
> Signed-off-by: Cong Wang <xiyou.wangcong@...il.com>
> ---
>   net/sched/sch_generic.c | 18 ++++++++++++++++++
>   1 file changed, 18 insertions(+)
>
> diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
> index 08f9fa27e06e..190570f21b20 100644
> --- a/net/sched/sch_generic.c
> +++ b/net/sched/sch_generic.c
> @@ -763,6 +763,23 @@ static void pfifo_fast_destroy(struct Qdisc *sch)
>   	}
>   }
>   
> +static int pfifo_fast_change_tx_queue_len(struct Qdisc *sch,
> +					  unsigned int new_len)
> +{
> +	struct pfifo_fast_priv *priv = qdisc_priv(sch);
> +	struct skb_array *bands[PFIFO_FAST_BANDS];
> +	int prio;
> +
> +	for (prio = 0; prio < PFIFO_FAST_BANDS; prio++) {
> +		struct skb_array *q = band2list(priv, prio);
> +
> +		bands[prio] = q;
> +	}
> +
> +	return skb_array_resize_multiple(bands, PFIFO_FAST_BANDS, new_len,
> +					 GFP_KERNEL);
> +}
> +
>   struct Qdisc_ops pfifo_fast_ops __read_mostly = {
>   	.id		=	"pfifo_fast",
>   	.priv_size	=	sizeof(struct pfifo_fast_priv),
> @@ -773,6 +790,7 @@ struct Qdisc_ops pfifo_fast_ops __read_mostly = {
>   	.destroy	=	pfifo_fast_destroy,
>   	.reset		=	pfifo_fast_reset,
>   	.dump		=	pfifo_fast_dump,
> +	.change_tx_queue_len =  pfifo_fast_change_tx_queue_len,
>   	.owner		=	THIS_MODULE,
>   	.static_flags	=	TCQ_F_NOLOCK | TCQ_F_CPUSTATS,
>   };

Is __skb_array_empty() in pfifo_fast_dequeue() still safe after this change?

Thanks