On Fri, Jul 25, 2014 at 11:50 AM, Willem de Bruijn <willemb@xxxxxxxxxx> 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. well, since you the author of this bit and you're ok with 'void *', I'm ok with it too :) Just typecast in kernel is still needed because of SK_RUN_FILTER() macro... -- 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
