On Fri, Jul 25, 2014 at 11:58 AM, Alexei Starovoitov <ast@xxxxxxxxxxxx> wrote: > 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... just tried with 'void *', actually all three type casts are needed... -- 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
