netdev - Re: [PATCH bpf-next] filter: add BPF_ADJ_ROOM_DATA mode to bpf_skb_adjust

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Message-ID: <20181112183939.xhiwgbqeaprvscu7@kafai-mbp.dhcp.thefacebook.com>
Date:   Mon, 12 Nov 2018 18:39:45 +0000
From:   Martin Lau <kafai@...com>
To:     Nicolas Dichtel <nicolas.dichtel@...nd.com>
CC:     "ast@...nel.org" <ast@...nel.org>,
        "daniel@...earbox.net" <daniel@...earbox.net>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH bpf-next] filter: add BPF_ADJ_ROOM_DATA mode to
 bpf_skb_adjust_room()

On Sun, Nov 11, 2018 at 12:43:27AM +0100, Nicolas Dichtel wrote:
> Le 09/11/2018 à 19:51, Martin Lau a écrit :
> > On Thu, Nov 08, 2018 at 04:11:37PM +0100, Nicolas Dichtel wrote:
> [snip]
> >> +static int bpf_skb_data_shrink(struct sk_buff *skb, u32 len)
> >> +{
> >> +	unsigned short hhlen = skb->dev->header_ops ?
> >> +			       skb->dev->hard_header_len : 0;
> >> +	int ret;
> >> +
> >> +	ret = skb_unclone(skb, GFP_ATOMIC);
> >> +	if (unlikely(ret < 0))
> >> +		return ret;
> >> +
> >> +	__skb_pull(skb, len);
> >> +	skb_reset_mac_header(skb);
> >> +	skb_reset_network_header(skb);
> >> +	skb->network_header += hhlen;
Nit. skb_set_network_header(skb, hhlen);

Othen than that

Acked-by: Martin KaFai Lau <kafai@...com>

> >> +	skb_reset_transport_header(skb);
> > hmm...why transport_header does not need += hhlen here
> > while network_header does?
> 
> network_header is mandatory because bpf_redirect(BPF_F_INGRESS) can be called
> and network_header is expected to be correctly set in this case.
> For transport_header, I choose to not set it, because the stack will set it
> later (for example ip_rcv_core()).
ic. make sense.