[lwip-devel] [task #13106] Add IPv6 scopes

[David van Moolenbroek]

Follow-up Comment #10, task #13106 (project lwip):

Comment #4:
> The only thing I'm not sure about is storing the scope in the netif
addresses. I would keep it separate.

Hm yeah, that should be fine as well actually. For the embedding case it may
be a bit cheaper to have the assigned address prepared for comparisons,
basically. With a separate scope field, that is less of an issue.

Comment #5:
> Just as a note to the scope ID: There is an u8_t netif->num - already
managed by netif code to be unique.

Ah yes. I remember looking into netif->num earlier and being a bit confused as
to what it wants to be, as some places seemed to be treating it as a per-name
unit number..

The bigger problem with netif->num is that it starts from zero, and it seems
that eg the slipif code even relies on that. That means that at the very
least, some remapping will be necessary, although that can be as simple as
#define netif_index(netif) ((netif)->num + 1). It's probably best to retain
the special value for "no scope" everywhere else.

Otherwise, netif->num would be fine, at least as long as it can be overridden
from the netif init callback, because if netif_num overflows, uniqueness is no
longer guaranteed. My implementation has to support dynamic interface
creation/destruction..

Comment #9:
> When you add the scope ID member AFTER the IP address, then struct ip_addr
won't increase in size (at least in dual-stack mode) since the scope member
and u8_t type fit into one u32_t alignment.

I believe that's only the case if both structures are packed, and I'm not sure
packing is a good idea here?

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