linux-kernel - Re: [PATCH net-next] net: filter: rename 'struct sk_filter' to 'struct bpf

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Date:	Fri, 25 Jul 2014 10:27:14 -0700
From:	Alexei Starovoitov <ast@...mgrid.com>
To:	Willem de Bruijn <willemb@...gle.com>
Cc:	Pablo Neira Ayuso <pablo@...filter.org>,
	Daniel Borkmann <dborkman@...hat.com>,
	"David S. Miller" <davem@...emloft.net>,
	Network Development <netdev@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	netfilter-devel <netfilter-devel@...r.kernel.org>
Subject: Re: [PATCH net-next] net: filter: rename 'struct sk_filter' to
 'struct bpf_prog'

On Fri, Jul 25, 2014 at 6:53 AM, Willem de Bruijn <willemb@...gle.com> wrote:
>>> >alternative fix for xt_bpf.h could be to replace:
>>> >         /* only used in the kernel */
>>> >     struct sk_filter *filter __attribute__((aligned(8)));
>>> >with
>>> >         /* only used in the kernel */
>>> >     void *filter __attribute__((aligned(8)));
>>> >
>>> >but this 'void *' approach may further break broken userspace,
>>> >whereas the fix implemented here is more seamless.
>>>
>>> Yep, that's not good, 'struct sk_filter' should never have been in a uapi
>>> file actually.
>
> 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.

> -#include <linux/filter.h>
>  #include <linux/types.h>
>
>  #define XT_BPF_MAX_NUM_INSTR   64
>
> +struct sk_filter;
> +
>  struct xt_bpf_info {
>
> I can send this as a separate patch to net-next, if that helps.
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