netdev - Re: [patch net-next v2 08/20] net: sched: cls_bpf: call block callbacks for offload

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Date:   Tue, 31 Oct 2017 17:44:09 -0700
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     Jiri Pirko <jiri@...nulli.us>
Cc:     netdev@...r.kernel.org, davem@...emloft.net, jhs@...atatu.com,
        xiyou.wangcong@...il.com, mlxsw@...lanox.com, andrew@...n.ch,
        vivien.didelot@...oirfairelinux.com, f.fainelli@...il.com,
        michael.chan@...adcom.com, ganeshgr@...lsio.com,
        jeffrey.t.kirsher@...el.com, saeedm@...lanox.com,
        matanb@...lanox.com, leonro@...lanox.com, idosch@...lanox.com,
        ast@...nel.org, daniel@...earbox.net, simon.horman@...ronome.com,
        pieter.jansenvanvuuren@...ronome.com, john.hurley@...ronome.com,
        alexander.h.duyck@...el.com
Subject: Re: [patch net-next v2 08/20] net: sched: cls_bpf: call block
 callbacks for offload

On Thu, 19 Oct 2017 15:50:36 +0200, Jiri Pirko wrote:
> @@ -159,17 +162,38 @@ static int cls_bpf_offload_cmd(struct tcf_proto *tp, struct cls_bpf_prog *prog,
>  	cls_bpf.exts_integrated = prog->exts_integrated;
>  	cls_bpf.gen_flags = prog->gen_flags;
>  
> -	err = dev->netdev_ops->ndo_setup_tc(dev, TC_SETUP_CLSBPF, &cls_bpf);
> -	if (!err && (cmd == TC_CLSBPF_ADD || cmd == TC_CLSBPF_REPLACE))
> -		prog->gen_flags |= TCA_CLS_FLAGS_IN_HW;
> +	if (tc_can_offload(dev)) {
> +		err = dev->netdev_ops->ndo_setup_tc(dev, TC_SETUP_CLSBPF,
> +						    &cls_bpf);
> +		if (addorrep) {
> +			if (err) {
> +				if (skip_sw)
> +					return err;
> +			} else {
> +				prog->gen_flags |= TCA_CLS_FLAGS_IN_HW;
> +			}
> +		}
> +	}
> +
> +	err = tc_setup_cb_call(block, NULL, TC_SETUP_CLSBPF, &cls_bpf, skip_sw);
> +	if (addorrep) {
> +		if (err < 0) {
> +			cls_bpf_offload_cmd(tp, prog, TC_CLSBPF_DESTROY);

It seems counter intuitive that the appropriate action for a failed
REPLACE is DESTROY.  One would expect a bad REPLACE X -> Y to be 
followed by a REPLACE Y -> X (i.e. go back to X).

At least my reading of cls_bpf is that if replace fails software path
will keep using the old prog.  Is this maybe something that's different
in flower?  Or am I reading the code wrong?