tools: ynl: don't skip regeneration from make targets

Commit 2b7ac0c87d98 ("tools: ynl-gen: don't touch the output file if
content is the same") is working too well. It was added so that
ynl-regen -f doesn't make us rebuild half of the kernel, if there
are no actual changes in any generated code.

When ynl-gen-c is called by make, however, we're better off trusting
make's tracking and overwrite the file. Otherwise if output is identical
we won't update file timestamps and make will retry code gen on every
invocation.

Link: https://lore.kernel.org/r/20231129193622.2912353-5-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

ynl: regenerate all headers

Also add support to pass topdir to ynl-regen.sh (Jakub) and call
it from the makefile to update the UAPI headers.

Signed-off-by: Stanislav Fomichev <sdf@google.com>
Co-developed-by: Jakub Kicinski <kuba@kernel.org>
Reviewed-by: Jakub Kicinski <kuba@kernel.org>
Link: https://lore.kernel.org/r/20230727163001.3952878-4-sdf@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

tools: ynl-gen: record extra args for regen

ynl-regen needs to know the arguments used to generate a file.
Record excluded ops and, while at it, user headers.

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

tools: ynl: user space helpers

Add "fixed" part of the user space Netlink Spec-based library.
This will get linked with the protocol implementations to form
a full API.

Acked-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

ynl: re-license uniformly under GPL-2.0 OR BSD-3-Clause

I was intending to make all the Netlink Spec code BSD-3-Clause
to ease the adoption but it appears that:
- I fumbled the uAPI and used "GPL WITH uAPI note" there
- it gives people pause as they expect GPL in the kernel
As suggested by Chuck re-license under dual. This gives us benefit
of full BSD freedom while fulfilling the broad "kernel is under GPL"
expectations.

Link: https://lore.kernel.org/all/20230304120108.05dd44c5@kernel.org/
Link: https://lore.kernel.org/r/20230306200457.3903854-1-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net: add basic C code generators for Netlink

Code generators to turn Netlink specs into C code.
I'm definitely not proud of it.

The main generator is in Python, there's a bash script
to regen all code-gen'ed files in tree after making
spec changes.

Acked-by: Stanislav Fomichev <sdf@google.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>