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

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Date:   Sun, 11 Nov 2018 00:43:27 +0100
From:   Nicolas Dichtel <nicolas.dichtel@...nd.com>
To:     Martin Lau <kafai@...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()

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;
>> +	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()).


Regards,
Nicolas