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Date:	Fri, 25 Jul 2014 11:43:05 -0700
From:	Alexei Starovoitov <>
To:	Willem de Bruijn <>
Cc:	Pablo Neira Ayuso <>,
	Daniel Borkmann <>,
	"David S. Miller" <>,
	Network Development <>,
	linux-kernel <>,
	netfilter-devel <>
Subject: Re: [PATCH net-next] net: filter: rename 'struct sk_filter' to
 'struct bpf_prog'

On Fri, Jul 25, 2014 at 11:32 AM, Willem de Bruijn <> wrote:
>>> This follows a convention in include/uapi/linux/netfilter/*.h that
>>> likely predates the introduction of uapi. A search for "Used
>>> internally by the kernel" shows many more examples. I should not have
>>> included filter.h, however. The common behavior when using pointers
>>> to kernel-internal structures is to have a forward declaration. I suggest
>>> making that change, instead of changing to void *. This avoids having
>>> to add casts where xt_bpf_info is used in net/netfilter/xt_bpf.c:
>> that will not avoid typecast.
>> Either 'void *' approach or extra 'struct sk_filter;' approach, both need
>> type casts to 'struct bpf_prog' in xt_bpf.c
>> (because of SK_RUN_FILTER macro)
>> Therefore I prefer extra 'struct sk_filter;' approach.
> I hadn't noticed that your patch makes the same change that I
> proposed. Nothing in userspace should touch that pointer, so it is
> fine to change its type to struct bpf_prog* at the same time. No need
> for typecasts.

really? I don't think it's a good idea to expose kernel struct type
to user space. How is it even going to compile?
#include <linux/filter.h> brings different files in kernel and in user space.
struct bpf_prog is undefined in user space and compiler will complain.
Adding 'struct bpf_prog;' will be ugly.
imo the lesser evil is adding 'struct sk_filter;' and doing type casts
in kernel.
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