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>

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 ("$(DEBUG)","1")
+  CFLAGS += -g -fsanitize=address -fsanitize=leak -static-libasan
+endif
+
+TOOL:=../ynl-gen-c.py
+
+GENS:=
+SRCS=$(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

tools/net/ynl/lib/Makefile

@@ -0,0 +1,28 @@
+# SPDX-License-Identifier: GPL-2.0
+
+CC=gcc
+CFLAGS=-std=gnu11 -O2 -W -Wall -Wextra -Wno-unused-parameter -Wshadow
+ifeq ("$(DEBUG)","1")
+  CFLAGS += -g -fsanitize=address -fsanitize=leak -static-libasan
+endif
+
+SRCS=$(wildcard *.c)
+OBJS=$(patsubst %.c,%.o,${SRCS})
+
+include $(wildcard *.d)
+
+all: ynl.a
+
+ynl.a: $(OBJS)
+	ar rcs $@ $(OBJS)
+clean:
+	rm -f *.o *.d *~
+
+hardclean: clean
+	rm -f *.a
+
+%.o: %.c
+	$(COMPILE.c) -MMD -c -o $@ $<
+
+.PHONY: all clean
+.DEFAULT_GOAL=all