In case of an error, the tx sync packet snip could previously have been
released twice. This moves re-attaching the tx sync snip down after the
last `goto error` to avoid this.
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.
When a VRB entry exists use minfwd to forward.
When a route exist for the first fragment received in reassembly create
a virtual reassembly buffer entry.
Non-routing 6LNs do not have to join the solicited nodes address, so
probing for a neighbor using that address may be in vain and only
spamming the LLN with unnecessary messages. RFC 6775 basically assumes
this in section 5.2:
> There is no need to join the solicited-node multicast address, since
> nobody multicasts NSs in this type of network.
In accordance with RFC 6775, section 5.2 an NCE should be set STALE
when an ARO renews the address registration for the address:
> The routers SHOULD NOT garbage-collect Registered NCEs (see
> Section 3.4), since they need to retain them until the Registration
> Lifetime expires. Similarly, if NUD on the router determines that
> the host is UNREACHABLE (based on the logic in [RFC4861]), the NCE
> SHOULD NOT be deleted but rather retained until the Registration
> Lifetime expires. A renewed ARO should mark the cache entry as
> STALE. Thus, for 6LoWPAN routers, the Neighbor Cache doesn't behave
> like a cache. Instead, it behaves as a registry of all the host
> addresses that are attached to the router.
When `nce` is NULL on the duplicate check, the later re-fetching of the
`nce` might result in an actual NCE entry that then contains a
duplicate, so we need to re-check the EUI-64 again as well.
This changes the prefixes of the symbols generated from USEMODULE and
USEPKG variables. The changes are as follow:
KCONFIG_MODULE_ => KCONFIG_USEMODULE_
KCONFIG_PKG_ => KCONFIG_USEPKG_
MODULE_ => USEMODULE_
PKG_ => USEPKG_
Replace direct accesses to sched_active_thread and sched_active_pid with
the helper functions thread_getpid() and thread_get_active(). This serves
two purposes:
1. It makes accidental writes to those variable from outside core less likely.
2. Casting off the volatile qualifier is now well contained to those two
functions
Coverty scan found this:
> CID 298295 (#1 of 1): Operands don't affect result (CONSTANT_EXPRESSION_RESULT) result_independent_of_operands:
> (ipv6_hdr_get_fl(ipv6_hdr) & 255) >> 8 is 0 regardless of the values of its operands.
Looking at the code, this appears to be a copy & paste error from the previous line.
Coverty scan found this:
> CID 298279 (#1 of 1): Out-of-bounds read (OVERRUN)
> 21. overrun-local: Overrunning array of 16 bytes at byte offset 64 by dereferencing pointer
The original intention was probably to advance the destination pointer by 4 bytes, not
4 * the destination type size.
Using pointer difference already gives us the number of elements of
size of what the pointer is pointing to.
Dividing by size will lead to the wrong (always 0) result.
