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. -- 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
