nlsysevent: add a genetlink(4) module to report kernel events

Hooked to devctl_notify, this allows consumers to received events
by subscribing to a system over a generic netlink protocol

Reviewed by:	imp, melifaro
Differential Revision:	https://reviews.freebsd.org/D37574

4 files changed, 220 insertions, 0 deletions

diff --git a/sys/modules/Makefile b/sys/modules/Makefile
index b9867f25df4e..f14dd383221f 100644
--- a/sys/modules/Makefile
+++ b/sys/modules/Makefile
@@ -282,6 +282,7 @@ SUBDIR=	\
 	nfsd \
 	nfslockd \
 	nfssvc \
+	nlsysevent \
 	nge \
 	nmdm \
 	nullfs \
diff --git a/sys/modules/nlsysevent/Makefile b/sys/modules/nlsysevent/Makefile
new file mode 100644
index 000000000000..d7d2100e3e66
--- /dev/null
+++ b/sys/modules/nlsysevent/Makefile
@@ -0,0 +1,11 @@
+# $FreeBSD$
+
+.PATH:	${SRCTOP}/sys/netlink/
+
+KMOD=	nlsysevent
+SRCS=	netlink_sysevent.c
+
+CFLAGS+=	-I${SRCTOP}/sys/contrib/netlink
+EXPORT_SYMS=	yes
+
+.include <bsd.kmod.mk>
diff --git a/sys/netlink/netlink_sysevent.c b/sys/netlink/netlink_sysevent.c
new file mode 100644
index 000000000000..67f18a3e2fe7
--- /dev/null
+++ b/sys/netlink/netlink_sysevent.c
@@ -0,0 +1,168 @@
+/*-
+ * SPDX-License-Identifier: BSD-2-Clause
+ *
+ * Copyright (c) 2023 Baptiste Daroussin <bapt@FreeBSD.org>
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include <sys/param.h>
+#include <sys/types.h>
+#include <sys/devctl.h>
+#include <sys/errno.h>
+#include <sys/module.h>
+#include <sys/kernel.h>
+#include <sys/malloc.h>
+#include <net/vnet.h>
+#include <netlink/netlink.h>
+#include <netlink/netlink_ctl.h>
+#include <netlink/netlink_generic.h>
+
+#include "netlink_sysevent.h"
+
+#define DEBUG_MOD_NAME  nl_sysevent
+#define DEBUG_MAX_LEVEL LOG_DEBUG3
+#include <netlink/netlink_debug.h>
+_DECLARE_DEBUG(LOG_INFO);
+
+MALLOC_DEFINE(M_NLSE, "nlsysevent", "Memory used for Netlink sysevent");
+#define	NLSE_FAMILY_NAME	"nlsysevent"
+static uint32_t ctrl_family_id;
+
+#define MAX_SYSEVENTS	64
+static struct sysevent {
+	char *name;
+	uint32_t id;
+} sysevents[MAX_SYSEVENTS] = {};
+
+static void
+sysevent_write(struct sysevent *se, const char *subsystem, const char *type,
+    const char *data)
+{
+	struct nl_writer nw = {};
+
+	if (!nlmsg_get_group_writer(&nw, NLMSG_LARGE, NETLINK_GENERIC, se->id)) {
+		NL_LOG(LOG_DEBUG, "error allocating group writer");
+		return;
+	}
+	struct nlmsghdr hdr = { .nlmsg_type = ctrl_family_id };
+	if (!nlmsg_reply(&nw, &hdr, sizeof(struct genlmsghdr))) {
+		return;
+	}
+
+	struct genlmsghdr *ghdr = nlmsg_reserve_object(&nw, struct genlmsghdr);
+	if (ghdr == NULL) {
+		NL_LOG(LOG_DEBUG, "unable to allocate memory");
+		return;
+	}
+	ghdr->version = 0;
+	ghdr->cmd = 0;
+	ghdr->reserved = 0;
+	nlattr_add_string(&nw, NLSE_ATTR_SYSTEM, se->name);
+	nlattr_add_string(&nw, NLSE_ATTR_SUBSYSTEM, subsystem);
+	nlattr_add_string(&nw, NLSE_ATTR_TYPE, type);
+	if (data != NULL)
+		nlattr_add_string(&nw, NLSE_ATTR_DATA, data);
+	nlmsg_end(&nw);
+	nlmsg_flush(&nw);
+}
+
+static void
+sysevent_send(const char *system, const char *subsystem, const char *type,
+    const char *data)
+{
+	struct sysevent *se = NULL;
+
+	for (size_t i = 0; i < MAX_SYSEVENTS; i++) {
+		if (sysevents[i].name == NULL) {
+			sysevents[i].name = strdup(system, M_NLSE);
+			sysevents[i].id = genl_register_group(NLSE_FAMILY_NAME,
+			    system);
+			se = &sysevents[i];
+			break;
+		}
+		if (strcmp(sysevents[i].name, system) == 0) {
+			se = &sysevents[i];
+			break;
+		}
+	}
+	if (se == NULL) {
+		NL_LOG(LOG_WARNING, "impossible to add the event %s, "
+		    "too many events\n", system);
+		return;
+	}
+
+	CURVNET_SET(vnet0);
+	sysevent_write(se, subsystem, type, data);
+	CURVNET_RESTORE();
+}
+
+static void
+nlsysevent_load(void)
+{
+	devctl_set_notify_hook(sysevent_send);
+	ctrl_family_id = genl_register_family(NLSE_FAMILY_NAME, 0, 2, NLSE_ATTR_MAX);
+	for (size_t i = 0; i < nitems(devctl_systems); i++) {
+		if (i >= MAX_SYSEVENTS) {
+			NL_LOG(LOG_WARNING, "impossible to add the event %s, too many events\n", devctl_systems[i]);
+			continue;
+		}
+		sysevents[i].name = strdup(devctl_systems[i], M_NLSE);
+		sysevents[i].id = genl_register_group(NLSE_FAMILY_NAME, devctl_systems[i]);
+	}
+}
+
+static void
+nlsysevent_unload(void)
+{
+	devctl_unset_notify_hook();
+	genl_unregister_family(NLSE_FAMILY_NAME);
+	for (size_t i = 0; i < MAX_SYSEVENTS; i++) {
+		if (sysevents[i].name == NULL)
+			break;
+		free(sysevents[i].name, M_NLSE);
+	}
+}
+
+static int
+nlsysevent_loader(module_t mod __unused, int what, void *priv __unused)
+{
+	int err = 0;
+
+	switch (what) {
+	case MOD_LOAD:
+		nlsysevent_load();
+		break;
+	case MOD_UNLOAD:
+		nlsysevent_unload();
+		break;
+	default:
+		err = EOPNOTSUPP;
+		break;
+	}
+	return (err);
+}
+static moduledata_t nlsysevent_mod = { "nlsysevent", nlsysevent_loader, NULL};
+
+DECLARE_MODULE(nlsysevent, nlsysevent_mod, SI_SUB_PSEUDO, SI_ORDER_ANY);
+MODULE_DEPEND(nlsysevent, netlink, 1, 1, 1);
+MODULE_VERSION(nlsysevent, 1);
diff --git a/sys/netlink/netlink_sysevent.h b/sys/netlink/netlink_sysevent.h
new file mode 100644
index 000000000000..23288d2dd5c3
--- /dev/null
+++ b/sys/netlink/netlink_sysevent.h
@@ -0,0 +1,40 @@
+/*-
+ * SPDX-License-Identifier: BSD-2-Clause
+ *
+ * Copyright (c) 2023 Baptiste Daroussin <bapt@FreeBSD.org>
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#ifndef _NETLINK_SYSEVENT_H_
+#define _NETLINK_SYSEVENT_H_
+
+enum {
+	NLSE_ATTR_UNSPEC = 0,
+	NLSE_ATTR_SYSTEM = 1,
+	NLSE_ATTR_SUBSYSTEM = 2,
+	NLSE_ATTR_TYPE = 3,
+	NLSE_ATTR_DATA = 4,
+	__NLSE_ATTR_MAX,
+};
+#define NLSE_ATTR_MAX (__NLSE_ATTR_MAX -1)
+#endif