On Fri, Jul 25, 2014 at 02:50:32PM -0400, Willem de Bruijn wrote: > On Fri, Jul 25, 2014 at 2:43 PM, Alexei Starovoitov <ast@xxxxxxxxxxxx> wrote: > > On Fri, Jul 25, 2014 at 11:32 AM, Willem de Bruijn <willemb@xxxxxxxxxx> 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? > > a forward declaration. > > > #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. > > but the exact same argument applies to sk_filter. If that struct is > renamed everywhere else, then the result will only be more confusing. > A forward declaration is the standard workaround to all such cases in > include/uapi/linux/netfilter. See for instance xt_connlimit.h. This is > sufficient to allow userspace build to succeed, without exposing any > kernel structure detail. If you don't even want to leak the name, then > let's make it void *. Keeping a declaration for sk_filter, while > sk_filter is renamed everywhere else is the least good option, in my > opinion. Please, send me a patch to remove that include <net/filter.h> from the uapi header and define struct sk_filter; so we save the typecast in xt_bpf.c The struct sk_filter; doesn't expose anything relevant since, even assuming userspace knows the layout, it can *not* do anything useful with that. Thanks. -- To unsubscribe from this list: send the line "unsubscribe netfilter-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
