If we get a large (e.g. /62) prefix from e.g. DHCPv6, we can split it
into subnets automatically to configure downstream interfaces.
This allows for automatic configuration of daisy-chained nodes or
nodes connected in a tree topology.
To enable the feature, a new pseudo-module `gnrc_ipv6_auto_subnets` is
provided.
The new `gnrc_tx_sync` module allows users of the GNRC network stack to
synchronize with the actual transmission of outgoing packets. This is directly
integrated into gnrc_sock. Hence, if `gnrc_tx_sync` is used, calls to e.g.
sock_udp_send() will block until the network stack has processed the message.
Use cases:
1. Prevent packet drop when sending at high rate
- If the application is sending faster than the stack can handle, the
message queues will overflow and outgoing packets are lost
2. Passing auxiliary data about the transmission back the stack
- When e.g. the number of required retransmissions, the transmission time
stamp, etc. should be made available to a user of an UDP sock, a
synchronization mechanism is needed
3. Simpler error reporting without footguns
- The current approach of using `core/msg` for passing up error messages is
difficult to use if other message come in. Currently, gnrc_sock is
busy-waiting and fetching messages from the message queue until the number
of expected status reports is received. It will enqueue all
non-status-report messages again at the end of the queue. This has
multiple issues:
- Busy waiting is especially in lower power scenarios with time slotted
MAC protocols harmful, as the CPU will remain active and consume
power even though the it could sleep until the TX slot is reached
- The status reports from the network stack are send to the user thread
blocking. If the message queue of the user thread is full, the network
stack would block until the user stack can fetch the messages. If
another higher priority thread would start sending a message, it
would busy wait for its status reports to completely come in. Hence,
the first thread doesn't get CPU time to fetch messages and unblock
the network stack. As a result, the system would lock up completely.
- Just adding the error/status code to the gnrc_tx_sync_t would preallocate
and reserve memory for the error reporting. That way gnrc_sock does not
need to search through the message queue for status reports and the
network stack does not need to block for the user thread fetching it.
Having the definitions sit in the `net/gnrc/sixlowpan/frag.h` header
does not make much sense, when using Selective Fragment Forwarding
(and the fragmentation buffer already includes a
`net/gnrc/sixlowpan/frag/stats.h` header), so they are moved to their
own header. Since with this change it makes more sense to have the
statistics stored in their own sub-module, the pseudo-module is also
actualized.
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
The packet buffer was originally designed to have a replaceable
back-end. This is why the actual module is called `gnrc_pktbuf_static`.
However, since than some auxiliary functions snuck into the static
back-end, which should go into the common module (which is a
pseudo-module at the moment).
This fix makes the `gnrc_pktbuf` pseudo-module an actual module and
moves the auxiliary functions to that module.
This ZEP implementation is based on `gnrc_netdev`, it is complicated to
use, I'm not even sure anyone used it except me or if it is working
still. See #6121 for a better port of ZEP.
