Replacing rtsock with netlink also means providing similar tracing facilities,
rtsock provides `route -n monitor` interface, where each message can be traced
to the originating PID.
This diff closes the feature gap between rtsock and netlink in that regard.
Netlink works slightly differently from rtsock, as it is a generic message
"broker". It calls some kernel KPIs and returns the result to the caller.
Other Netlink consumers gets notified on the changed kernel state using the
relevant subsystem callbacks. Typically, it is close to impossible to pass
some data through these KPIs to enhance the notification.
This diff approaches the problem by using osd(9) to assign the relevant
socket pointer (`'nlp`) to the per-socket taskqueue execution thread.
This change allows to recover the pointer in the aforementioned notification
callbacks and extract some additional data.
Using `osd(9)` (and adding additional metadata) to the notification receiver
comes with some additional cost attached, so this interface needs to be
enabled explicitly by using a newly-created `NETLINK_MSG_INFO` `SOL_NETLINK`
socket option.
The actual medatadata (which includes the originator PID) is provided via
control messages. To enable extensibility, the control message data is
encoded in the standard netlink(TLV-based) fashion. The list of the
currently-provided properties can be found in `nlmsginfo_attrs`.
snl(3) is extended to enable decoding of netlink messages with metadata
(`snl_read_message_dbg()` stores the parsed structure in the provided buffer).
Differential Revision: https://reviews.freebsd.org/D39391
route.c uses newroute() to handle the "route get" command. The logic
inside newroute() adds RTF_GATEWAY flag if "-interface" flag is not
specified. That results in the inconsistent RTM_GET message with
RTF_GATEWAY set but no RTAX_GATEWAY provided. Address this in the
translation code by checking if the gateway is actually provided.
This change converts all kernel rtsock interactions in route(8)
to Netlink.
Based on the WITHOUT_NETLINK_SUPPORT src.conf(5) variable, route(8)
now fully operates either via Netlink or via rtsock/sysctl.
The default (compile-time) is Netlink.
The output for route delete/add/get/flush is targeted to be exactly
the same (apart from some error handling cases).
The output for the route monitor has been changed to improve
readability and support netlink models.
Other behaviour changes:
* exact prefix lookup (route -n get a.b.c.d/e) is not yet supported.
* route monitor does not show the change originator yet.
Differential Revision: https://reviews.freebsd.org/D39007
