linux-kernel - Re: [PATCH net-next 05/11] tuntap: tweak on the path of non-xdp case in tun_build

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Date:   Thu, 6 Sep 2018 13:16:17 -0400
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH net-next 05/11] tuntap: tweak on the path of non-xdp case
 in tun_build_skb()

On Thu, Sep 06, 2018 at 12:05:20PM +0800, Jason Wang wrote:
> If we're sure not to go native XDP, there's no need for several things
> like bh and rcu stuffs.
> 
> Signed-off-by: Jason Wang <jasowang@...hat.com>

True...

> ---
>  drivers/net/tun.c | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
> index f8cdcfa392c3..389aa0727cc6 100644
> --- a/drivers/net/tun.c
> +++ b/drivers/net/tun.c
> @@ -1675,10 +1675,12 @@ static struct sk_buff *tun_build_skb(struct tun_struct *tun,
>  	 * of xdp_prog above, this should be rare and for simplicity
>  	 * we do XDP on skb in case the headroom is not enough.
>  	 */
> -	if (hdr->gso_type || !xdp_prog)
> +	if (hdr->gso_type || !xdp_prog) {
>  		*skb_xdp = 1;
> -	else
> -		*skb_xdp = 0;
> +		goto build;
> +	}
> +
> +	*skb_xdp = 0;
>  
>  	local_bh_disable();
>  	rcu_read_lock();
> @@ -1724,6 +1726,7 @@ static struct sk_buff *tun_build_skb(struct tun_struct *tun,
>  	rcu_read_unlock();
>  	local_bh_enable();
>  
> +build:

But this is spaghetti code. Please just put common
code into functions and call them, don't goto.

>  	skb = build_skb(buf, buflen);
>  	if (!skb) {
>  		skb = ERR_PTR(-ENOMEM);
> -- 
> 2.17.1