Add a sample application for WireGuard, using the generated C library.

The main benefit of this is to exercise the generated library,
which might be useful for future self-tests.

Example:
  $ make -C tools/net/ynl/lib
  $ make -C tools/net/ynl/generated
  $ make -C tools/net/ynl/tests wireguard
  $ ./tools/net/ynl/tests/wireguard
  usage: ./tools/net/ynl/tests/wireguard <ifindex|ifname>
  $ sudo ./tools/net/ynl/tests/wireguard wg-test
  Interface 3: wg-test
      Peer 6adfb183a4a2c94a2f92dab5ade762a4788[...]:
          Data: rx: 42 / tx: 42 bytes
          Allowed IPs:
              0.0.0.0/0
              ::/0

Signed-off-by: Asbjørn Sloth Tønnesen <ast@fiberby.net>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Link: https://patch.msgid.link/20260414153944.2742252-3-Jason@zx2c4.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

YnlFamily opens an AF_NETLINK socket in __init__ but has no way
to release it other than leaving it to the GC. YnlFamily holds a
self reference cycle through SpecFamily's self.family = self
in its super().__init__() call, so refcount GC cannot reclaim
it and the socket stays open until the cyclic GC runs.

If a test creates a guest netns, instantiates a YnlFamily inside
it via NetNSEnter(), performs some test case work via Ynl, and
then deletes the netns, then the 'ip netns del' only drops the
mount binding and cleanup_net in the kernel never runs, so any
subsequent test case assertions that objects got cleaned up would
fail given this only gets triggered later via cyclic GC run.

Add an explicit close() that closes the netlink socket and wire
up the __enter__/__exit__ so callers can scope the instance
deterministically via 'with YnlFamily(...) as ynl: ...'.

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: Nikolay Aleksandrov <razor@blackwall.org>
Link: https://patch.msgid.link/20260413220809.604592-2-daniel@iogearbox.net
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Add a --dbg-small-recv debug option to control the recv() buffer size
used by YNL, matching the same option already present in cli.py. This
is useful if user need to get large netlink message.

Signed-off-by: Hangbin Liu <liuhangbin@gmail.com>
Link: https://patch.msgid.link/20260408-b4-ynl_ethtool-v2-3-7623a5e8f70b@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Rename the local helper doit() to do_set() and dumpit() to do_get() to
better reflect their purpose.

Convert do_get() to use ynl.do() with an explicit device header instead
of ynl.dump() followed by client-side filtering. This is more efficient
as the kernel only processes and returns data for the requested device,
rather than dumping all devices across the netns.

Signed-off-by: Hangbin Liu <liuhangbin@gmail.com>
Link: https://patch.msgid.link/20260408-b4-ynl_ethtool-v2-2-7623a5e8f70b@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

We have converted all the samples to selftests. This script is
the last piece of random "PoC" code we still have lying around.
Let's move it to tests.

Signed-off-by: Hangbin Liu <liuhangbin@gmail.com>
Link: https://patch.msgid.link/20260408-b4-ynl_ethtool-v2-1-7623a5e8f70b@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

The ../generated/protos.a rule had a spurious leading space before the
target name. In make, target rules must start at column 0; only recipe
lines are indented with a tab. The extra space caused make to misparse
the rule.

Remove the leading space to match the style of the adjacent
../lib/ynl.a rule.

Fixes: e0aa0c61758f ("tools: ynl: move samples to tests")
Signed-off-by: Hangbin Liu <liuhangbin@gmail.com>
Link: https://patch.msgid.link/20260408-ynl_makefile-v1-1-f9624acc2ad9@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Donald points out that the current naive implementation using dicts
breaks if policy is recursive (child nest uses policy idx already
used by its parent).

Lean more into the NlPolicy class. This lets us "render" the policy
on demand, when user accesses it. If someone wants to do an infinite
walk that's on them :) Show policy info as attributes of the class
and use dict format to descend into sub-policies for extra neatness.

Reviewed-by: Donald Hunter <donald.hunter@gmail.com>
Link: https://patch.msgid.link/20260313232047.2068518-1-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Add --policy flag which can be combined with --do or --dump to query
the kernel's netlink policy for an operation instead of executing it.

Examples:

  $ ynl --family netdev --do dev-get --policy
  {'ifindex': {'max-value': 4294967295, 'min-value': 1, 'type': 'u32'}}

  $ ynl --family ethtool --do channels-get --policy --output-json
  {"header": {"type": "nested", "policy": {"dev-index": ...}}}

  $ ynl --family netdev --dump dev-get --policy
  {}

Link: https://patch.msgid.link/20260310005337.3594225-6-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

The format of Netlink policy dump is a bit curious with messages
in the same dump carrying both attrs and mapping info. Plus each
message carries a single piece of the puzzle the caller must then
reassemble.

I need to do this reassembly for a test, but I think it's generally
useful. So let's add proper support to YnlFamily to return more
user-friendly representation. See the various docs in the patch
for more details.

Link: https://patch.msgid.link/20260310005337.3594225-5-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

The class is quite long. It's getting hard to find the user-facing
methods. Add a short doc at the class level explaining the main API.

Link: https://patch.msgid.link/20260310005337.3594225-4-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>