This imports the protocol parameters for Selective Fragment Recovery
(SFR). For the values I took some educated guesses based on my
experience with previous experimentation with fragment forwarding.
The defines currently are based on [draft v7].
[draft v7]: https://tools.ietf.org/html/draft-ietf-6lo-fragment-recovery-07#section-7.1
fixup! gnrc_sixlowpan_frag: initial import of SRF parameters
The name `fragment_msg` or `frag_msg`/`msg_frag` always to me was a bit
misplaced, as it basically implements an asynchronous fragmentation
buffer and doesn't necessarily have anything to do with messages.
This change
1. changes the name to `fb` (for fragmentation buffer)
2. factors its code out to its own sub-module so it can be re-used by
other 6LoWPAN fragmentation schemes like [Selective Fragment
Recovery]
[Selective Fragment Recovery]: https://tools.ietf.org/html/draft-ietf-6lo-fragment-recovery-05
This module was intended to be a test framework for GNRC but it never
really got used. It was not maintained for 3 years. It will be removed
after 2020.07 release at the latest.
The functions now are semantic distinct:
- gnrc_netif_is_6lo(): the interface is a 6Lo interface
- gnrc_netif_is_6ln(): the interface is using Neighbor Discovery
according to RFC 6775
Preparation step to introduce a semantic difference between an
interface being a 6Lo interface and a 6LN according to RFC 6775 [[1]]
(i.e. performs Neighbor Discovery as defined there).
[1]: https://tools.ietf.org/html/rfc6775#section-2
Rather than dispatching the packet automatically once it is complete,
`gnrc_sixlowpan_frag_rb_add()` now only returns success, and leaves it
to the caller to dispatch the packet.
Due to some changes to the minimal forwarding draft and in preparation
for Selective Fragment Recovery some changes to the VRB API were
needed. Now the index of a VRB entry is only (L2 src, tag) not as
before (L2 src, L2 dst, length, tag).
I know that the current `rbuf_base` causes waste, as all the fields not
used by the new index are effectively not used by the VRB. I'd like to
fix that however in a later change, since that also requires some
modifications of the classic reassembly buffer, and thus would
complicate the review and testing of the change.
Sources for the index change:
- https://tools.ietf.org/html/draft-ietf-6lo-minimal-fragment-04#section-1
- https://mailarchive.ietf.org/arch/browse/6lo/?gbt=1&index=DLCTxC2X4bRNtYPHhtEkavMWlz4
