[ovs-dev] [flow-compat 5/7] netlink: New macro NL_POLICY_FOR.

[Jesse Gross]

On Mon, Nov 7, 2011 at 1:28 PM, Ben Pfaff <blp at nicira.com> wrote:
> On Mon, Nov 07, 2011 at 11:03:11AM -0800, Jesse Gross wrote:
>> On Mon, Nov 7, 2011 at 9:22 AM, Ben Pfaff <blp at nicira.com> wrote:
>> > The kernel netlink code is not as picky as ours, BTW: generally it
>> > only validates minimum lengths. ??Maybe we should only do that in
>> > userspace too; it would simplify a few things. ??Any thoughts on that?
>>
>> Does anyone ever try to send extended structures that are the same at
>> the beginning but have extra information at the end?  It would be a
>> somewhat weird form of compatibility code but it would depend on only
>> checking the min length.
>
> The libnl manual page here alleges that extensions are done this way
> "frequently":
>        http://www.infradead.org/~tgr/libnl/doc/core.html
>
> I guess I should go through and drop most uses of maxlen.

Interesting, I don't think I've ever seen something that does this in practice.

>> Otherwise, I don't have particularly strong feelings.  Would it
>> actually simplify things all that much though?
>
> I was thinking that we could drop maxlen entirely, but in fact it's
> pretty useful for string data, so no, it wouldn't really simplify
> anything.  Never mind.

Yeah, I think it's useful in general but it sounds like we shouldn't
be using it for structures.