netdev - Re: [PATCH net-next] ebpf, filter: do not convert skb->protocol to host endianess during runtime

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Date:	Fri, 20 Mar 2015 15:24:48 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	daniel@...earbox.net
Cc:	ast@...mgrid.com, netdev@...r.kernel.org
Subject: Re: [PATCH net-next] ebpf, filter: do not convert skb->protocol to
 host endianess during runtime

From: Daniel Borkmann <daniel@...earbox.net>
Date: Thu, 19 Mar 2015 19:38:27 +0100

> Commit c24973957975 ("bpf: allow BPF programs access 'protocol' and 'vlan_tci'
> fields") has added support for accessing protocol, vlan_present and vlan_tci
> into the skb offset map.
> 
> As referenced in the below discussion, accessing skb->protocol from an eBPF
> program should be converted without handling endianess.
> 
> The reason for this is that an eBPF program could simply do a check more
> naturally, by f.e. testing skb->protocol == htons(ETH_P_IP), where the LLVM
> compiler resolves htons() against a constant automatically during compilation
> time, as opposed to an otherwise needed run time conversion.
> 
> After all, the way of programming both from a user perspective differs quite
> a lot, i.e. bpf_asm ["ld proto"] versus a C subset/LLVM.
> 
> Reference: https://patchwork.ozlabs.org/patch/450819/
> Signed-off-by: Daniel Borkmann <daniel@...earbox.net>

Applied, thanks Daniel.
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