linux: make linux_netlink_p->msg_from_linux be able to fail

The KPI for this function was misleading. From the NetLink perspective it
looked like a function that: a) allocates new hdr, b) can fail. Neither
was true. Let the function return a error code instead of returning the
same hdr it was passed to. In case if future Linux NetLink compatibility
support calls for reallocating header, pass hdr as pointer to pointer.

With KPI that returns a error, propagate domain conversion errors all the
way up to NetLink module. This fixes panic when unknown domain is
converted to 0xff and this invalid value is passed into NetLink
processing.

PR: 274536
Reviewed by: melifaro
Differential Revision: https://reviews.freebsd.org/D44392

netlink: avoid putting empty mbufs on the socket queue

When processing incoming Netlink messages in nl_process_nbuf() kernel
always allocates a writer with a buffer to put generated reply to.
However, certain messages aren't replied. That makes nlmsg_flush()
to put an empty buffer to the socket. Avoid doing that because avoiding
is much easier than dealing with empty buffers on the receiver side.

netlink: fix regression with group writers

Refactoring of argument list to nl_send_one() led to derefercing
wrong union member. Rename nl_send_one() to a more generic name,
isolate anew nl_send_one() as the callback only for the normal
writer and provide correct argument to nl_send() from nl_send_group().

Fixes: ff5ad900d2a0793659241eee96be53e6053b5081

netlink: refactor control data generation for recvmsg(2)

Netlink should return a very simple control data on every recvmsg(2)
syscall. This data is associated with a syscall, not with an nlmsg,
neither with internal our internal representation (nl_bufs). There is
no need to pre-allocate it in non-sleepable context and attach to
nl_buf. Allocate right in the syscall with M_WAITOK. This also
shaves lots of code and simplifies things.

Reviewed by: melifaro
Differential Revision: https://reviews.freebsd.org/D42989

netlink: use protocol specific receive buffer

Implement Netlink socket receive buffer as a simple TAILQ of nl_buf's,
same part of struct sockbuf that is used for send buffer already.
This shaves a lot of code and a lot of extra processing. The pcb rids
of the I/O queues as the socket buffer is exactly the queue. The
message writer is simplified a lot, as we now always deal with linear
buf. Notion of different buffer types goes away as way as different
kinds of writers. The only things remaining are: a socket writer and
a group writer.
The impact on the network stack is that we no longer use mbufs, so
a workaround from d18715475071 disappears.

Note on message throttling. Now the taskqueue throttling mechanism
needs to look at both socket buffers protected by their respective
locks and on flags in the pcb that are protected by the pcb lock.
There is definitely some room for optimization, but this changes tries
to preserve as much as possible.

Note on new nl_soreceive(). It emulates soreceive_generic(). It
must undergo further optimization, see large comment put in there.

Note on tests/sys/netlink/test_netlink_message_writer.py. This test
boiled down almost to nothing with mbufs removed. However, I left
it with minimal functionality (it basically checks that allocating N
bytes we get N bytes) as it is one of not so many examples of ktest
framework that allows to test KPIs with python.

Note on Linux support. It got much simplier: Netlink message writer
loses notion of Linux support lifetime, it is same regardless of
process ABI. On socket write from Linux process we perform
conversion immediately in nl_receive_message() and on an output
conversion to Linux happens in in nl_send_one(). XXX: both
conversions use M_NOWAIT allocation, which used to be the case
before this change, too.

Reviewed by: melifaro
Differential Revision: https://reviews.freebsd.org/D42524

netlink: use domain specific send buffer

Instead of using generic socket code, create Netlink specific socket
buffer. It is a simple TAILQ of writes that came from userland. This
saves us one memory allocation that could fail and one memory copy.

Reviewed by: melifaro
Differential Revision: https://reviews.freebsd.org/D42522

sys: Automated cleanup of cdefs and other formatting

Apply the following automated changes to try to eliminate
no-longer-needed sys/cdefs.h includes as well as now-empty
blank lines in a row.

Remove /^#if.*\n#endif.*\n#include\s+<sys/cdefs.h>.*\n/
Remove /\n+#include\s+<sys/cdefs.h>.*\n+#if.*\n#endif.*\n+/
Remove /\n+#if.*\n#endif.*\n+/
Remove /^#if.*\n#endif.*\n/
Remove /\n+#include\s+<sys/cdefs.h>\n#include\s+<sys/types.h>/
Remove /\n+#include\s+<sys/cdefs.h>\n#include\s+<sys/param.h>/
Remove /\n+#include\s+<sys/cdefs.h>\n#include\s+<sys/capsicum.h>/

Sponsored by: Netflix

netlink: move NETLINK define to opt_global.h

Move the NETLINK define into opt_global.h so we can rely on it being
set correctly, without having to remember to include opt_netlink.h.
This ensures that the NETLINK define is correctly set. If not we
may end up with unloadable modules, due to missing symbols (such as
nlmsg_get_group_writer).

PR: 274306
Reviewed by: imp, markj
MFC after: 3 days
Differential Revision: https://reviews.freebsd.org/D42179

sys: Remove $FreeBSD$: one-line .c pattern

Remove /^[\s*]*__FBSDID\("\$FreeBSD\$"\);?\s*\n/

spdx: The BSD-2-Clause-FreeBSD identifier is obsolete, drop -FreeBSD

The SPDX folks have obsoleted the BSD-2-Clause-FreeBSD identifier. Catch
up to that fact and revert to their recommended match of BSD-2-Clause.

Discussed with: pfg
MFC After: 3 days
Sponsored by: Netflix

netlink: reduce default log levels

Reduce the default log level for netlink to LOG_INFO. This removes a
number of messages such as

> [nl_iface] dump_sa: unsupported family: 0, skipping
or
> [nl_iface] get_operstate_ether: error calling SIOCGIFMEDIA on vlan0: 22

that are useful for debugging, but not for most users.

Reviewed by: melifaro
Sponsored by: Rubicon Communications, LLC ("Netgate")
Differential Revision: https://reviews.freebsd.org/D40062

netlink: fix debug message on 32-bit archs

route: show originator PID in netlink monitor

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

netlink: add netlink KPI to the kernel by default

This change does the following:

Base Netlink KPIs (ability to register the family, parse and/or
write a Netlink message) are always present in the kernel. Specifically,
* Implementation of genetlink family/group registration/removal,
some base accessors (netlink_generic_kpi.c, 260 LoC) are compiled in
unconditionally.
* Basic TLV parser functions (netlink_message_parser.c, 507 LoC) are
compiled in unconditionally.
* Glue functions (netlink<>rtsock), malloc/core sysctl definitions
(netlink_glue.c, 259 LoC) are compiled in unconditionally.
* The rest of the KPI _functions_ are defined in the netlink_glue.c,
but their implementation calls a pointer to either the stub function
or the actual function, depending on whether the module is loaded or not.

This approach allows to have only 1k LoC out of ~3.7k LoC (current
sys/netlink implementation) in the kernel, which will not grow further.
It also allows for the generic netlink kernel customers to load
successfully without requiring Netlink module and operate correctly
once Netlink module is loaded.

Reviewed by: imp
MFC after: 2 weeks
Differential Revision: https://reviews.freebsd.org/D39269

netlink: do not crash when linux message translation fails.

CID: 1498889
MFC after: 2 weeks

netlink: suppress sending NLMSG_ERROR if NLMSG_DONE is already sent

Netlink has a confirmation/error reporting mechanism for the sent
messages. Kernel explicitly acks each messages if requested (NLM_F_ACK)
or if message processing results in an error.
Similarly, for multipart messages - typically dumps, where each message
represents a single object like an interface or a route - another
message, NLMSG_DONE is used to indicate the end of dump and the
resulting status.
As a result, successfull dump ends with both NLMSG_DONE and NLMSG_ERROR
messages.
RFC 3549 does not say anything specific about such case.
Linux adopted an optimisation which suppresses NLMSG_ERROR message
when NLMSG_DONE is already sent. Certain libraries/applications like
libnl depends on such behavior.

Suppress sending NLMSG_ERROR if NLMSG_DONE is already sent, by
setting newly-added 'suppress_ack' flag in the writer and checking
this flag when generating ack.

This change restores libnl compatibility.

Before:
```
~ nl-link-list
Error: Unable to allocate link cache: Message sequence number mismatch
````

After:
```
~ nl-link-list
vtnet0 ether 52:54:00:14:e3:19 <broadcast,multicast,up,running>
lo0 ieee1394 <loopback,multicast,up,running>
```

Reviewed by: bapt,pauamma
Tested by: bapt
Differential Revision: https://reviews.freebsd.org/D37565

netlink: Fix build without VIMAGE

netlink: fix format strings on 32-bit platforms

netlink: add netlink support

Netlinks is a communication protocol currently used in Linux kernel to modify,
read and subscribe for nearly all networking state. Interfaces, addresses, routes,
firewall, fibs, vnets, etc are controlled via netlink.
It is async, TLV-based protocol, providing 1-1 and 1-many communications.

The current implementation supports the subset of NETLINK_ROUTE
family. To be more specific, the following is supported:
* Dumps:
- routes
- nexthops / nexthop groups
- interfaces
- interface addresses
- neighbors (arp/ndp)
* Notifications:
- interface arrival/departure
- interface address arrival/departure
- route addition/deletion
* Modifications:
- adding/deleting routes
- adding/deleting nexthops/nexthops groups
- adding/deleting neghbors
- adding/deleting interfaces (basic support only)
* Rtsock interaction
- route events are bridged both ways

The implementation also supports the NETLINK_GENERIC family framework.

Implementation notes:
Netlink is implemented via loadable/unloadable kernel module,
not touching many kernel parts.
Each netlink socket uses dedicated taskqueue to support async operations
that can sleep, such as interface creation. All message processing is
performed within these taskqueues.

Compatibility:
Most of the Netlink data models specified above maps to FreeBSD concepts
nicely. Unmodified ip(8) binary correctly works with
interfaces, addresses, routes, nexthops and nexthop groups. Some
software such as net/bird require header-only modifications to compile
and work with FreeBSD netlink.

Reviewed by: imp
Differential Revision: https://reviews.freebsd.org/D36002
MFC after: 2 months