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

tools/net/ynl/lib/ynl.h

@@ -0,0 +1,237 @@
+// SPDX-License-Identifier: GPL-2.0 OR BSD-3-Clause
+#ifndef __YNL_C_H
+#define __YNL_C_H 1
+
+#include <stddef.h>
+#include <libmnl/libmnl.h>
+#include <linux/genetlink.h>
+#include <linux/types.h>
+
+struct mnl_socket;
+struct nlmsghdr;
+
+/*
+ * User facing code
+ */
+
+struct ynl_ntf_base_type;
+struct ynl_ntf_info;
+struct ynl_sock;
+
+enum ynl_error_code {
+	YNL_ERROR_NONE = 0,
+	__YNL_ERRNO_END = 4096,
+	YNL_ERROR_INTERNAL,
+	YNL_ERROR_EXPECT_ACK,
+	YNL_ERROR_EXPECT_MSG,
+	YNL_ERROR_UNEXPECT_MSG,
+	YNL_ERROR_ATTR_MISSING,
+	YNL_ERROR_ATTR_INVALID,
+	YNL_ERROR_UNKNOWN_NTF,
+	YNL_ERROR_INV_RESP,
+};
+
+/**
+ * struct ynl_error - error encountered by YNL
+ * @code:	errno (low values) or YNL error code (enum ynl_error_code)
+ * @attr_offs:	offset of bad attribute (for very advanced users)
+ * @msg:	error message
+ *
+ * Error information for when YNL operations fail.
+ * Users should interact with the err member of struct ynl_sock directly.
+ * The main exception to that rule is ynl_sock_create().
+ */
+struct ynl_error {
+	enum ynl_error_code code;
+	unsigned int attr_offs;
+	char msg[512];
+};
+
+/**
+ * struct ynl_family - YNL family info
+ * Family description generated by codegen. Pass to ynl_sock_create().
+ */
+struct ynl_family {
+/* private: */
+	const char *name;
+	const struct ynl_ntf_info *ntf_info;
+	unsigned int ntf_info_size;
+};
+
+/**
+ * struct ynl_sock - YNL wrapped netlink socket
+ * @err: YNL error descriptor, cleared on every request.
+ */
+struct ynl_sock {
+	struct ynl_error err;
+
+/* private: */
+	const struct ynl_family *family;
+	struct mnl_socket *sock;
+	__u32 seq;
+	__u32 portid;
+	__u16 family_id;
+
+	unsigned int n_mcast_groups;
+	struct {
+		unsigned int id;
+		char name[GENL_NAMSIZ];
+	} *mcast_groups;
+
+	struct ynl_ntf_base_type *ntf_first;
+	struct ynl_ntf_base_type **ntf_last_next;
+
+	struct nlmsghdr *nlh;
+	struct ynl_policy_nest *req_policy;
+	unsigned char *tx_buf;
+	unsigned char *rx_buf;
+	unsigned char raw_buf[];
+};
+
+struct ynl_sock *
+ynl_sock_create(const struct ynl_family *yf, struct ynl_error *e);
+void ynl_sock_destroy(struct ynl_sock *ys);
+
+#define ynl_dump_foreach(dump, iter)					\
+	for (typeof(dump->obj) *iter = &dump->obj;			\
+	     !ynl_dump_obj_is_last(iter);				\
+	     iter = ynl_dump_obj_next(iter))
+
+int ynl_subscribe(struct ynl_sock *ys, const char *grp_name);
+int ynl_socket_get_fd(struct ynl_sock *ys);
+int ynl_ntf_check(struct ynl_sock *ys);
+
+/**
+ * ynl_has_ntf() - check if socket has *parsed* notifications
+ * @ys: active YNL socket
+ *
+ * Note that this does not take into account notifications sitting
+ * in netlink socket, just the notifications which have already been
+ * read and parsed (e.g. during a ynl_ntf_check() call).
+ */
+static inline bool ynl_has_ntf(struct ynl_sock *ys)
+{
+	return ys->ntf_last_next != &ys->ntf_first;
+}
+struct ynl_ntf_base_type *ynl_ntf_dequeue(struct ynl_sock *ys);
+
+void ynl_ntf_free(struct ynl_ntf_base_type *ntf);
+
+/*
+ * YNL internals / low level stuff
+ */
+
+/* Generic mnl helper code */
+
+enum ynl_policy_type {
+	YNL_PT_REJECT = 1,
+	YNL_PT_IGNORE,
+	YNL_PT_NEST,
+	YNL_PT_FLAG,
+	YNL_PT_BINARY,
+	YNL_PT_U8,
+	YNL_PT_U16,
+	YNL_PT_U32,
+	YNL_PT_U64,
+	YNL_PT_NUL_STR,
+};
+
+struct ynl_policy_attr {
+	enum ynl_policy_type type;
+	unsigned int len;
+	const char *name;
+	struct ynl_policy_nest *nest;
+};
+
+struct ynl_policy_nest {
+	unsigned int max_attr;
+	struct ynl_policy_attr *table;
+};
+
+struct ynl_parse_arg {
+	struct ynl_sock *ys;
+	struct ynl_policy_nest *rsp_policy;
+	void *data;
+};
+
+struct ynl_dump_list_type {
+	struct ynl_dump_list_type *next;
+	unsigned char data[] __attribute__ ((aligned (8)));
+};
+extern struct ynl_dump_list_type *YNL_LIST_END;
+
+static inline bool ynl_dump_obj_is_last(void *obj)
+{
+	unsigned long uptr = (unsigned long)obj;
+
+	uptr -= offsetof(struct ynl_dump_list_type, data);
+	return uptr == (unsigned long)YNL_LIST_END;
+}
+
+static inline void *ynl_dump_obj_next(void *obj)
+{
+	unsigned long uptr = (unsigned long)obj;
+	struct ynl_dump_list_type *list;
+
+	uptr -= offsetof(struct ynl_dump_list_type, data);
+	list = (void *)uptr;
+	uptr = (unsigned long)list->next;
+	uptr += offsetof(struct ynl_dump_list_type, data);
+
+	return (void *)uptr;
+}
+
+struct ynl_ntf_base_type {
+	__u16 family;
+	__u8 cmd;
+	struct ynl_ntf_base_type *next;
+	void (*free)(struct ynl_ntf_base_type *ntf);
+	unsigned char data[] __attribute__ ((aligned (8)));
+};
+
+extern mnl_cb_t ynl_cb_array[NLMSG_MIN_TYPE];
+
+struct nlmsghdr *
+ynl_gemsg_start_req(struct ynl_sock *ys, __u32 id, __u8 cmd, __u8 version);
+struct nlmsghdr *
+ynl_gemsg_start_dump(struct ynl_sock *ys, __u32 id, __u8 cmd, __u8 version);
+
+int ynl_attr_validate(struct ynl_parse_arg *yarg, const struct nlattr *attr);
+
+int ynl_recv_ack(struct ynl_sock *ys, int ret);
+int ynl_cb_null(const struct nlmsghdr *nlh, void *data);
+
+/* YNL specific helpers used by the auto-generated code */
+
+struct ynl_req_state {
+	struct ynl_parse_arg yarg;
+	mnl_cb_t cb;
+	__u32 rsp_cmd;
+};
+
+struct ynl_dump_state {
+	struct ynl_sock *ys;
+	struct ynl_policy_nest *rsp_policy;
+	void *first;
+	struct ynl_dump_list_type *last;
+	size_t alloc_sz;
+	mnl_cb_t cb;
+	__u32 rsp_cmd;
+};
+
+struct ynl_ntf_info {
+	struct ynl_policy_nest *policy;
+	mnl_cb_t cb;
+	size_t alloc_sz;
+	void (*free)(struct ynl_ntf_base_type *ntf);
+};
+
+int ynl_exec(struct ynl_sock *ys, struct nlmsghdr *req_nlh,
+	     struct ynl_req_state *yrs);
+int ynl_exec_dump(struct ynl_sock *ys, struct nlmsghdr *req_nlh,
+		  struct ynl_dump_state *yds);
+
+void ynl_error_unknown_notification(struct ynl_sock *ys, __u8 cmd);
+int ynl_error_parse(struct ynl_parse_arg *yarg, const char *msg);
+
+#endif

tools/net/ynl/ynl-regen.sh

@@ -14,7 +14,7 @@ done
 
 KDIR=$(dirname $(dirname $(dirname $(dirname $(realpath $0)))))
 
-files=$(git grep --files-with-matches '^/\* YNL-GEN \(kernel\|uapi\)')
+files=$(git grep --files-with-matches '^/\* YNL-GEN \(kernel\|uapi\|user\)')
 for f in $files; do
     # params:     0       1      2     3
     #         $YAML YNL-GEN kernel $mode