Re: [PATCH nf 3/4] netfilter: conntrack_ftp: prefer skb_linearize

[Florian Westphal <fw@strlen.de>]

Alexander Duyck <alexanderduyck@fb.com> wrote:
> > -	spin_lock_bh(&nf_ftp_lock);
> > -	fb_ptr = skb_header_pointer(skb, dataoff, datalen, ftp_buffer);
> > -	if (!fb_ptr) {
> > -		spin_unlock_bh(&nf_ftp_lock);
> > -		return NF_ACCEPT;
> > -	}
> > +	spin_lock_bh(&ct->lock);
> > +	fb_ptr = skb->data + dataoff;
> > 
> >  	ends_in_nl = (fb_ptr[datalen - 1] == '\n');
> >  	seq = ntohl(th->seq) + datalen;
> 
> Rather than using skb_header_pointer/skb_linearize is there any reason why you couldn't use pskb_may_pull? It seems like that would be much closer to what you are looking for here rather than linearizing the entire buffer. With that you would have access to all the same headers you did with the skb_header_pointer approach and in most cases the copy should just be skipped since the headlen is already in the skb->data buffer.

This helper is written with the assumption that everything is searchable
via 'const char *'.

I'm not going to submit a patch to -net that rewrites this,
and I'm not sure its worth it to spend time on it for -next either.