Merge branch 'tools-ynl-user-space-c'

Jakub Kicinski says:

====================
tools: ynl: user space C

Use the code gen which is already in tree to generate a user space
library for a handful of simple families. I find YNL C quite useful
in some WIP projects, and I think others may find it useful, too.
I was hoping someone will pick this work up and finish it...
but it seems that Python YNL has largely stolen the thunder.
Python may not be great for selftest, tho, and actually this lib
is more fully-featured. The Python script was meant as a quick demo,
funny how those things go.

v2: https://lore.kernel.org/all/20230604175843.662084-1-kuba@kernel.org/
v1: https://lore.kernel.org/all/20230603052547.631384-1-kuba@kernel.org/
====================

Link: https://lore.kernel.org/r/20230605190108.809439-1-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Documentation/userspace-api/netlink/intro-specs.rst

@@ -78,3 +78,82 @@ to see other examples.
 The code generation itself is performed by ``tools/net/ynl/ynl-gen-c.py``
 but it takes a few arguments so calling it directly for each file
 quickly becomes tedious.
+
+YNL lib
+=======
+
+``tools/net/ynl/lib/`` contains an implementation of a C library
+(based on libmnl) which integrates with code generated by
+``tools/net/ynl/ynl-gen-c.py`` to create easy to use netlink wrappers.
+
+YNL basics
+----------
+
+The YNL library consists of two parts - the generic code (functions
+prefix by ``ynl_``) and per-family auto-generated code (prefixed
+with the name of the family).
+
+To create a YNL socket call ynl_sock_create() passing the family
+struct (family structs are exported by the auto-generated code).
+ynl_sock_destroy() closes the socket.
+
+YNL requests
+------------
+
+Steps for issuing YNL requests are best explained on an example.
+All the functions and types in this example come from the auto-generated
+code (for the netdev family in this case):
+
+.. code-block:: c
+
+   // 0. Request and response pointers
+   struct netdev_dev_get_req *req;
+   struct netdev_dev_get_rsp *d;
+
+   // 1. Allocate a request
+   req = netdev_dev_get_req_alloc();
+   // 2. Set request parameters (as needed)
+   netdev_dev_get_req_set_ifindex(req, ifindex);
+
+   // 3. Issues the request
+   d = netdev_dev_get(ys, req);
+   // 4. Free the request arguments
+   netdev_dev_get_req_free(req);
+   // 5. Error check (the return value from step 3)
+   if (!d) {
+	// 6. Print the YNL-generated error
+	fprintf(stderr, "YNL: %s\n", ys->err.msg);
+        return -1;
+   }
+
+   // ... do stuff with the response @d
+
+   // 7. Free response
+   netdev_dev_get_rsp_free(d);
+
+YNL dumps
+---------
+
+Performing dumps follows similar pattern as requests.
+Dumps return a list of objects terminated by a special marker,
+or NULL on error. Use ``ynl_dump_foreach()`` to iterate over
+the result.
+
+YNL notifications
+-----------------
+
+YNL lib supports using the same socket for notifications and
+requests. In case notifications arrive during processing of a request
+they are queued internally and can be retrieved at a later time.
+
+To subscribed to notifications use ``ynl_subscribe()``.
+The notifications have to be read out from the socket,
+``ynl_socket_get_fd()`` returns the underlying socket fd which can
+be plugged into appropriate asynchronous IO API like ``poll``,
+or ``select``.
+
+Notifications can be retrieved using ``ynl_ntf_dequeue()`` and have
+to be freed using ``ynl_ntf_free()``. Since we don't know the notification
+type upfront the notifications are returned as ``struct ynl_ntf_base_type *``
+and user is expected to cast them to the appropriate full type based
+on the ``cmd`` member.

tools/net/ynl/Makefile

@@ -0,0 +1,19 @@
+# SPDX-License-Identifier: GPL-2.0
+
+SUBDIRS = lib generated samples
+
+all: $(SUBDIRS)
+
+$(SUBDIRS):
+	@if [ -f "$@/Makefile" ] ; then \
+		$(MAKE) -C $@ ; \
+	fi
+
+clean hardclean:
+	@for dir in $(SUBDIRS) ; do \
+		if [ -f "$$dir/Makefile" ] ; then \
+			$(MAKE) -C $$dir $@; \
+		fi \
+	done
+
+.PHONY: clean all $(SUBDIRS)

tools/net/ynl/generated/Makefile

@@ -0,0 +1,45 @@
+# SPDX-License-Identifier: GPL-2.0
+
+CC=gcc
+CFLAGS=-std=gnu11 -O2 -W -Wall -Wextra -Wno-unused-parameter -Wshadow \
+	-I../lib/
+ifeq ("$(DEBUG)","1")
+  CFLAGS += -g -fsanitize=address -fsanitize=leak -static-libasan
+endif
+
+TOOL:=../ynl-gen-c.py
+
+GENS:=fou netdev
+SRCS=$(patsubst %,%-user.c,${GENS})
+HDRS=$(patsubst %,%-user.h,${GENS})
+OBJS=$(patsubst %,%-user.o,${GENS})
+
+all: protos.a $(HDRS) $(SRCS) $(KHDRS) $(KSRCS) $(UAPI) regen
+
+protos.a: $(OBJS)
+	@echo -e "\tAR $@"
+	@ar rcs $@ $(OBJS)
+
+%-user.h: ../../../../Documentation/netlink/specs/%.yaml $(TOOL)
+	@echo -e "\tGEN $@"
+	@$(TOOL) --mode user --header --spec $< > $@
+
+%-user.c: ../../../../Documentation/netlink/specs/%.yaml $(TOOL)
+	@echo -e "\tGEN $@"
+	@$(TOOL) --mode user --source --spec $< > $@
+
+%-user.o: %-user.c %-user.h
+	@echo -e "\tCC $@"
+	@$(COMPILE.c) -c -o $@ $<
+
+clean:
+	rm -f *.o
+
+hardclean: clean
+	rm -f *.c *.h *.a
+
+regen:
+	@../ynl-regen.sh
+
+.PHONY: all clean hardclean regen
+.DEFAULT_GOAL: all