Re: [PATCH 2/2] netlink: add ethernet address policy types

On Thu, Sep 13, 2018 at 02:16:06PM +0200, Johannes Berg wrote:

On Thu, 2018-09-13 at 14:12 +0200, Michal Kubecek wrote:

quoted

On Thu, Sep 13, 2018 at 02:02:53PM +0200, Johannes Berg wrote:

quoted

On Thu, 2018-09-13 at 13:58 +0200, Michal Kubecek wrote:

quoted

The code looks correct to me but I have some doubts. Having a special
policy for MAC addresses may lead to adding one for IPv4 address (maybe
not, we can use NLA_U32 for them), IPv6 addresses and other data types
with fixed length. Wouldn't it be more helpful to add a variant of
NLA_BINARY (NLA_BINARY_EXACT?) which would fail/warn if attribute length
isn't equal to .len?

Yeah, I guess we could do that, and then

#define NLA_ETH_ADDR .len = ETH_ALEN, .type = NLA_BINARY_EXACT
#define NLA_IP6_ADDR .len = 16, .type = NLA_BINARY_EXACT

or so?

Maybe rather

  #define NLA_ETH_ADDR NLA_BINARY_EXACT, .len = ETH_ALEN
  #define NLA_IP6_ADDR NLA_BINARY_EXACT, .len = sizeof(struct in6_addr)

so that one could write

  { .type = NLA_ETH_ADDR }

Yeah, that's possible. I considered it for a second, but it was slightly
too magical for my taste :-)

Better pick a different "namespace", perhaps NLA_POLICY_ETH_ADDR or so?

Right, that sounds better. I'm afraid anything too tricky would
inevitably trick people into using it in an unexpected way and ending up
with very confusing error messages.

Michal Kubecek