initHEADmaster

13 files changed, 1176 insertions, 0 deletions

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..a28ffa6
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,10 @@
+.cache/
+compile_commands.json
+*.ko
+*.cmd
+*.o
+*.mod
+*.mod.*
+*.symvers
+*.order
+us/genltest
diff --git a/README.md b/README.md
new file mode 100644
index 0000000..6b02651
--- /dev/null
+++ b/README.md
@@ -0,0 +1,30 @@
+# Generic Netlink example
+
+This repository contains an example of how to use the Generic Netlink
+communication protocol of the Linux Kernel both in kernel space and user space.
+
+For more information read my introductory article
+[here](https://www.yaroslavps.com/weblog/genl-intro/); or if you are the
+adventurous kind just read the source, it's got plenty of comments :)
+
+## Build and run
+
+### Kernel module
+
+In order to build the kernel module you need to have installed the Linux kernel
+headers in your system.
+
+Once you've got the requirements covered just switch to the `ks/` directory and 
+`make` it.
+
+If the build completed successfully, you should be able to load the
+`genltest.ko` module using insmod.
+
+### User space program
+
+In order to build the program you need to have libnl installed.
+
+Once installed just switch to the `us/` directory and `make` it.
+
+If the build completed successfully, and once you have loaded the aforementioned
+`genltest.ko` module, you should be able to run the program `./genltest`.
diff --git a/ks/.exrc b/ks/.exrc
new file mode 100644
index 0000000..cc55546
--- /dev/null
+++ b/ks/.exrc
@@ -0,0 +1,4 @@
+let ch_syntax_for_h = 1
+set ts=8
+set sw=8
+lua vim.diagnostic.disable()
diff --git a/ks/COPYING b/ks/COPYING
new file mode 100644
index 0000000..3d4fad0
--- /dev/null
+++ b/ks/COPYING
@@ -0,0 +1,7 @@
+Copyright (c) 2022 Yaroslav de la Peña Smirnov
+
+This is free software, which you can redistribute and/or modify under the terms
+of the GNU General Public License, version 2.0 only, unless otherwise noted
+inside of individual source files. It is provided AS IS and WITHOUT ANY WARRANTY
+whatsoever. For more information read the LICENSE file and/or the individual
+source file.
diff --git a/ks/LICENSE b/ks/LICENSE
new file mode 100644
index 0000000..d159169
--- /dev/null
+++ b/ks/LICENSE
@@ -0,0 +1,339 @@
+                    GNU GENERAL PUBLIC LICENSE
+                       Version 2, June 1991
+
+ Copyright (C) 1989, 1991 Free Software Foundation, Inc.,
+ 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ Everyone is permitted to copy and distribute verbatim copies
+ of this license document, but changing it is not allowed.
+
+                            Preamble
+
+  The licenses for most software are designed to take away your
+freedom to share and change it.  By contrast, the GNU General Public
+License is intended to guarantee your freedom to share and change free
+software--to make sure the software is free for all its users.  This
+General Public License applies to most of the Free Software
+Foundation's software and to any other program whose authors commit to
+using it.  (Some other Free Software Foundation software is covered by
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+your programs, too.
+
+  When we speak of free software, we are referring to freedom, not
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+   TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION
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+    This program is free software; you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
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+    (at your option) any later version.
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+    This program is distributed in the hope that it will be useful,
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+    You should have received a copy of the GNU General Public License along
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+Also add information on how to contact you by electronic and paper mail.
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+    This is free software, and you are welcome to redistribute it
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+The hypothetical commands `show w' and `show c' should show the appropriate
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+
+  <signature of Ty Coon>, 1 April 1989
+  Ty Coon, President of Vice
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+This General Public License does not permit incorporating your program into
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+library.  If this is what you want to do, use the GNU Lesser General
+Public License instead of this License.
diff --git a/ks/Makefile b/ks/Makefile
new file mode 100644
index 0000000..54301de
--- /dev/null
+++ b/ks/Makefile
@@ -0,0 +1,11 @@
+KERNELDIR := /lib/modules/$(shell uname -r)/build
+# CFLAGS_genltest.o := -O0
+obj-m += genltest.o
+
+all:
+	$(MAKE) -C $(KERNELDIR) V=0  M=`pwd` modules
+clean:
+	#$(MAKE) -C $(KERNELDIR)  M=`pwd` clean
+	@rm -f *.ko *.o modules.order Module.symvers *.mod.? *~
+	@rm -rf .tmp_versions .cache.mk *.ur-safe *.mod
+
diff --git a/ks/genltest.c b/ks/genltest.c
new file mode 100644
index 0000000..fa9a960
--- /dev/null
+++ b/ks/genltest.c
@@ -0,0 +1,215 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Generic Netlink example module
+ *
+ * An example on how to use the Generic Netlink API with ops and multicast
+ * groups.
+ *
+ *  Copyright (c) 2022 Yaroslav de la Peña Smirnov <yps@yaroslavps.com>
+ */
+#define pr_fmt(fmt) "genltest: " fmt
+
+#include "genltest.h"
+
+#include <linux/module.h>
+#include <net/genetlink.h>
+
+/*
+ * Some materials that were used as source for this example/tutorial/guide:
+ *
+ * - https://wiki.linuxfoundation.org/networking/generic_netlink_howto
+ * - https://kernel.org/doc/html/next/userspace-api/netlink/intro.html
+ */
+
+#define MSG_MAX_LEN 1024
+
+/* Forward declaration */
+static struct genl_family genl_fam;
+
+/* Handler for GENLTEST_CMD_ECHO messages received */
+static int echo_doit(struct sk_buff *skb, struct genl_info *info)
+{
+	int		ret = 0;
+	void	       *hdr;
+	struct sk_buff *msg;
+
+	/* Check if the attribute is present and print it */
+	if (info->attrs[GENLTEST_A_MSG]) {
+		char *str = nla_data(info->attrs[GENLTEST_A_MSG]);
+		pr_info("message received: %s\n", str);
+	} else {
+		pr_info("empty message received\n");
+	}
+
+	/* Allocate a new buffer for the reply */
+	msg = nlmsg_new(NLMSG_DEFAULT_SIZE, GFP_KERNEL);
+	if (!msg) {
+		pr_err("failed to allocate message buffer\n");
+		return -ENOMEM;
+	}
+
+	/* Put the Generic Netlink header */
+	hdr = genlmsg_put(msg, info->snd_portid, info->snd_seq, &genl_fam, 0,
+			  GENLTEST_CMD_ECHO);
+	if (!hdr) {
+		pr_err("failed to create genetlink header\n");
+		nlmsg_free(msg);
+		return -EMSGSIZE;
+	}
+	/* And the message */
+	if ((ret = nla_put_string(msg, GENLTEST_A_MSG,
+				  "Hello from Kernel Space, Netlink!"))) {
+		pr_err("failed to create message string\n");
+		genlmsg_cancel(msg, hdr);
+		nlmsg_free(msg);
+		goto out;
+	}
+
+	/* Finalize the message and send it */
+	genlmsg_end(msg, hdr);
+
+	ret = genlmsg_reply(msg, info);
+	pr_info("reply sent\n");
+
+out:
+	return ret;
+}
+
+/* Attribute validation policy for our echo command */
+static struct nla_policy echo_pol[GENLTEST_A_MAX + 1] = {
+	[GENLTEST_A_MSG] = { .type = NLA_NUL_STRING },
+};
+
+/* Operations for our Generic Netlink family */
+static struct genl_ops genl_ops[] = {
+	{
+		.cmd	= GENLTEST_CMD_ECHO,
+		.policy = echo_pol,
+		.doit	= echo_doit,
+	 },
+};
+
+/* Multicast groups for our family */
+static const struct genl_multicast_group genl_mcgrps[] = {
+	{ .name = GENLTEST_MC_GRP_NAME },
+};
+
+/* Generic Netlink family */
+static struct genl_family genl_fam = {
+	.name	  = GENLTEST_GENL_NAME,
+	.version  = GENLTEST_GENL_VERSION,
+	.maxattr  = GENLTEST_A_MAX,
+	.ops	  = genl_ops,
+	.n_ops	  = ARRAY_SIZE(genl_ops),
+	.mcgrps	  = genl_mcgrps,
+	.n_mcgrps = ARRAY_SIZE(genl_mcgrps),
+};
+
+/* Multicast ping message to our genl multicast group */
+static int echo_ping(const char *buf, size_t cnt)
+{
+	int		ret = 0;
+	void	       *hdr;
+	/* Allocate message buffer */
+	struct sk_buff *skb = genlmsg_new(NLMSG_DEFAULT_SIZE, GFP_KERNEL);
+
+	if (unlikely(!skb)) {
+		pr_err("failed to allocate memory for genl message\n");
+		return -ENOMEM;
+	}
+
+	/* Put the Generic Netlink header */
+	hdr = genlmsg_put(skb, 0, 0, &genl_fam, 0, GENLTEST_CMD_ECHO);
+	if (unlikely(!hdr)) {
+		pr_err("failed to allocate memory for genl header\n");
+		nlmsg_free(skb);
+		return -ENOMEM;
+	}
+
+	/* And the message */
+	if ((ret = nla_put_string(skb, GENLTEST_A_MSG, buf))) {
+		pr_err("unable to create message string\n");
+		genlmsg_cancel(skb, hdr);
+		nlmsg_free(skb);
+		return ret;
+	}
+
+	/* Finalize the message */
+	genlmsg_end(skb, hdr);
+
+	/* Send it over multicast to the 0-th mc group in our array. */
+	ret = genlmsg_multicast(&genl_fam, skb, 0, 0, GFP_KERNEL);
+	if (ret == -ESRCH) {
+		pr_warn("multicast message sent, but nobody was listening...\n");
+	} else if (ret) {
+		pr_err("failed to send multicast genl message\n");
+	} else {
+		pr_info("multicast message sent\n");
+	}
+
+	return ret;
+}
+
+/*
+ * Test sysfs attr to send multicast messages. The string in the buffer will be 
+ * echoed to the multicast group.
+ */
+static ssize_t ping_store(struct kobject *kobj, struct kobj_attribute *attr,
+			  const char *buf, size_t cnt)
+{
+	int max = cnt > MSG_MAX_LEN ? MSG_MAX_LEN : cnt;
+	echo_ping(buf, max);
+
+	return max;
+}
+
+static struct kobject	    *kobj;
+static struct kobj_attribute ping_attr = __ATTR_WO(ping);
+
+static int __init init_genltest(void)
+{
+	int ret = 0;
+
+	pr_info("init start\n");
+
+	kobj = kobject_create_and_add("genltest", kobj);
+	if (unlikely(!kobj)) {
+		pr_err("unable to create kobject\n");
+		return -ENOMEM;
+	}
+	ret = sysfs_create_file(kobj, &ping_attr.attr);
+	if (unlikely(ret)) {
+		pr_err("unable to create sysfs file\n");
+		kobject_put(kobj);
+		return ret;
+	}
+
+	ret = genl_register_family(&genl_fam);
+	if (unlikely(ret)) {
+		pr_crit("failed to register generic netlink family\n");
+		sysfs_remove_file(kobj, &ping_attr.attr);
+		kobject_put(kobj);
+	}
+
+	pr_info("init end\n");
+
+	return ret;
+}
+
+static void __exit exit_genltest(void)
+{
+	if (unlikely(genl_unregister_family(&genl_fam))) {
+		pr_err("failed to unregister generic netlink family\n");
+	}
+
+	sysfs_remove_file(kobj, &ping_attr.attr);
+	kobject_put(kobj);
+
+	pr_info("exit\n");
+}
+
+MODULE_AUTHOR("Yaroslav de la Peña Smirnov");
+MODULE_LICENSE("GPL");
+
+module_init(init_genltest);
+module_exit(exit_genltest);
diff --git a/ks/genltest.h b/ks/genltest.h
new file mode 100644
index 0000000..bd947a3
--- /dev/null
+++ b/ks/genltest.h
@@ -0,0 +1,31 @@
+#ifndef GENLTEST_H
+#define GENLTEST_H
+
+/*
+ * This header includes definitions that are shared with kernel space and user
+ * space. This header would be put in a place visible to user space.
+ */
+
+#define GENLTEST_GENL_NAME "genltest"
+#define GENLTEST_GENL_VERSION 1
+#define GENLTEST_MC_GRP_NAME "mcgrp"
+
+/* Attributes */
+enum genltest_attrs {
+	GENLTEST_A_UNSPEC,
+	GENLTEST_A_MSG,
+	__GENLTEST_A_MAX,
+};
+
+#define GENLTEST_A_MAX (__GENLTEST_A_MAX - 1)
+
+/* Commands */
+enum genltest_cmds {
+	GENLTEST_CMD_UNSPEC,
+	GENLTEST_CMD_ECHO,
+	__GENLTEST_CMD_MAX,
+};
+
+#define GENLTEST_CMD_MAX (__GENLTEST_CMD_MAX - 1)
+
+#endif 
diff --git a/us/.exrc b/us/.exrc
new file mode 100644
index 0000000..8d44102
--- /dev/null
+++ b/us/.exrc
@@ -0,0 +1,3 @@
+let ch_syntax_for_h = 1
+set ts=8
+set sw=8
diff --git a/us/COPYING b/us/COPYING
new file mode 100644
index 0000000..3d4fad0
--- /dev/null
+++ b/us/COPYING
@@ -0,0 +1,7 @@
+Copyright (c) 2022 Yaroslav de la Peña Smirnov
+
+This is free software, which you can redistribute and/or modify under the terms
+of the GNU General Public License, version 2.0 only, unless otherwise noted
+inside of individual source files. It is provided AS IS and WITHOUT ANY WARRANTY
+whatsoever. For more information read the LICENSE file and/or the individual
+source file.
diff --git a/us/LICENSE b/us/LICENSE
new file mode 100644
index 0000000..d159169
--- /dev/null
+++ b/us/LICENSE
@@ -0,0 +1,339 @@
+                    GNU GENERAL PUBLIC LICENSE
+                       Version 2, June 1991
+
+ Copyright (C) 1989, 1991 Free Software Foundation, Inc.,
+ 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ Everyone is permitted to copy and distribute verbatim copies
+ of this license document, but changing it is not allowed.
+
+                            Preamble
+
+  The licenses for most software are designed to take away your
+freedom to share and change it.  By contrast, the GNU General Public
+License is intended to guarantee your freedom to share and change free
+software--to make sure the software is free for all its users.  This
+General Public License applies to most of the Free Software
+Foundation's software and to any other program whose authors commit to
+using it.  (Some other Free Software Foundation software is covered by
+the GNU Lesser General Public License instead.)  You can apply it to
+your programs, too.
+
+  When we speak of free software, we are referring to freedom, not
+price.  Our General Public Licenses are designed to make sure that you
+have the freedom to distribute copies of free software (and charge for
+this service if you wish), that you receive source code or can get it
+if you want it, that you can change the software or use pieces of it
+in new free programs; and that you know you can do these things.
+
+  To protect your rights, we need to make restrictions that forbid
+anyone to deny you these rights or to ask you to surrender the rights.
+These restrictions translate to certain responsibilities for you if you
+distribute copies of the software, or if you modify it.
+
+  For example, if you distribute copies of such a program, whether
+gratis or for a fee, you must give the recipients all the rights that
+you have.  You must make sure that they, too, receive or can get the
+source code.  And you must show them these terms so they know their
+rights.
+
+  We protect your rights with two steps: (1) copyright the software, and
+(2) offer you this license which gives you legal permission to copy,
+distribute and/or modify the software.
+
+  Also, for each author's protection and ours, we want to make certain
+that everyone understands that there is no warranty for this free
+software.  If the software is modified by someone else and passed on, we
+want its recipients to know that what they have is not the original, so
+that any problems introduced by others will not reflect on the original
+authors' reputations.
+
+  Finally, any free program is threatened constantly by software
+patents.  We wish to avoid the danger that redistributors of a free
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+program proprietary.  To prevent this, we have made it clear that any
+patent must be licensed for everyone's free use or not licensed at all.
+
+  The precise terms and conditions for copying, distribution and
+modification follow.
+
+                    GNU GENERAL PUBLIC LICENSE
+   TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION
+
+  0. This License applies to any program or other work which contains
+a notice placed by the copyright holder saying it may be distributed
+under the terms of this General Public License.  The "Program", below,
+refers to any such program or work, and a "work based on the Program"
+means either the Program or any derivative work under copyright law:
+that is to say, a work containing the Program or a portion of it,
+either verbatim or with modifications and/or translated into another
+language.  (Hereinafter, translation is included without limitation in
+the term "modification".)  Each licensee is addressed as "you".
+
+Activities other than copying, distribution and modification are not
+covered by this License; they are outside its scope.  The act of
+running the Program is not restricted, and the output from the Program
+is covered only if its contents constitute a work based on the
+Program (independent of having been made by running the Program).
+Whether that is true depends on what the Program does.
+
+  1. You may copy and distribute verbatim copies of the Program's
+source code as you receive it, in any medium, provided that you
+conspicuously and appropriately publish on each copy an appropriate
+copyright notice and disclaimer of warranty; keep intact all the
+notices that refer to this License and to the absence of any warranty;
+and give any other recipients of the Program a copy of this License
+along with the Program.
+
+You may charge a fee for the physical act of transferring a copy, and
+you may at your option offer warranty protection in exchange for a fee.
+
+  2. You may modify your copy or copies of the Program or any portion
+of it, thus forming a work based on the Program, and copy and
+distribute such modifications or work under the terms of Section 1
+above, provided that you also meet all of these conditions:
+
+    a) You must cause the modified files to carry prominent notices
+    stating that you changed the files and the date of any change.
+
+    b) You must cause any work that you distribute or publish, that in
+    whole or in part contains or is derived from the Program or any
+    part thereof, to be licensed as a whole at no charge to all third
+    parties under the terms of this License.
+
+    c) If the modified program normally reads commands interactively
+    when run, you must cause it, when started running for such
+    interactive use in the most ordinary way, to print or display an
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+    notice that there is no warranty (or else, saying that you provide
+    a warranty) and that users may redistribute the program under
+    these conditions, and telling the user how to view a copy of this
+    License.  (Exception: if the Program itself is interactive but
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+    the Program is not required to print an announcement.)
+
+These requirements apply to the modified work as a whole.  If
+identifiable sections of that work are not derived from the Program,
+and can be reasonably considered independent and separate works in
+themselves, then this License, and its terms, do not apply to those
+sections when you distribute them as separate works.  But when you
+distribute the same sections as part of a whole which is a work based
+on the Program, the distribution of the whole must be on the terms of
+this License, whose permissions for other licensees extend to the
+entire whole, and thus to each and every part regardless of who wrote it.
+
+Thus, it is not the intent of this section to claim rights or contest
+your rights to work written entirely by you; rather, the intent is to
+exercise the right to control the distribution of derivative or
+collective works based on the Program.
+
+In addition, mere aggregation of another work not based on the Program
+with the Program (or with a work based on the Program) on a volume of
+a storage or distribution medium does not bring the other work under
+the scope of this License.
+
+  3. You may copy and distribute the Program (or a work based on it,
+under Section 2) in object code or executable form under the terms of
+Sections 1 and 2 above provided that you also do one of the following:
+
+    a) Accompany it with the complete corresponding machine-readable
+    source code, which must be distributed under the terms of Sections
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+    b) Accompany it with a written offer, valid for at least three
+    years, to give any third party, for a charge no more than your
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+
+    c) Accompany it with the information you received as to the offer
+    to distribute corresponding source code.  (This alternative is
+    allowed only for noncommercial distribution and only if you
+    received the program in object code or executable form with such
+    an offer, in accord with Subsection b above.)
+
+The source code for a work means the preferred form of the work for
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+
+If distribution of executable or object code is made by offering
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+access to copy the source code from the same place counts as
+distribution of the source code, even though third parties are not
+compelled to copy the source along with the object code.
+
+  4. You may not copy, modify, sublicense, or distribute the Program
+except as expressly provided under this License.  Any attempt
+otherwise to copy, modify, sublicense or distribute the Program is
+void, and will automatically terminate your rights under this License.
+However, parties who have received copies, or rights, from you under
+this License will not have their licenses terminated so long as such
+parties remain in full compliance.
+
+  5. You are not required to accept this License, since you have not
+signed it.  However, nothing else grants you permission to modify or
+distribute the Program or its derivative works.  These actions are
+prohibited by law if you do not accept this License.  Therefore, by
+modifying or distributing the Program (or any work based on the
+Program), you indicate your acceptance of this License to do so, and
+all its terms and conditions for copying, distributing or modifying
+the Program or works based on it.
+
+  6. Each time you redistribute the Program (or any work based on the
+Program), the recipient automatically receives a license from the
+original licensor to copy, distribute or modify the Program subject to
+these terms and conditions.  You may not impose any further
+restrictions on the recipients' exercise of the rights granted herein.
+You are not responsible for enforcing compliance by third parties to
+this License.
+
+  7. If, as a consequence of a court judgment or allegation of patent
+infringement or for any other reason (not limited to patent issues),
+conditions are imposed on you (whether by court order, agreement or
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+distribute so as to satisfy simultaneously your obligations under this
+License and any other pertinent obligations, then as a consequence you
+may not distribute the Program at all.  For example, if a patent
+license would not permit royalty-free redistribution of the Program by
+all those who receive copies directly or indirectly through you, then
+the only way you could satisfy both it and this License would be to
+refrain entirely from distribution of the Program.
+
+If any portion of this section is held invalid or unenforceable under
+any particular circumstance, the balance of the section is intended to
+apply and the section as a whole is intended to apply in other
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+
+It is not the purpose of this section to induce you to infringe any
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+implemented by public license practices.  Many people have made
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+through that system in reliance on consistent application of that
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+to distribute software through any other system and a licensee cannot
+impose that choice.
+
+This section is intended to make thoroughly clear what is believed to
+be a consequence of the rest of this License.
+
+  8. If the distribution and/or use of the Program is restricted in
+certain countries either by patents or by copyrighted interfaces, the
+original copyright holder who places the Program under this License
+may add an explicit geographical distribution limitation excluding
+those countries, so that distribution is permitted only in or among
+countries not thus excluded.  In such case, this License incorporates
+the limitation as if written in the body of this License.
+
+  9. The Free Software Foundation may publish revised and/or new versions
+of the General Public License from time to time.  Such new versions will
+be similar in spirit to the present version, but may differ in detail to
+address new problems or concerns.
+
+Each version is given a distinguishing version number.  If the Program
+specifies a version number of this License which applies to it and "any
+later version", you have the option of following the terms and conditions
+either of that version or of any later version published by the Free
+Software Foundation.  If the Program does not specify a version number of
+this License, you may choose any version ever published by the Free Software
+Foundation.
+
+  10. If you wish to incorporate parts of the Program into other free
+programs whose distribution conditions are different, write to the author
+to ask for permission.  For software which is copyrighted by the Free
+Software Foundation, write to the Free Software Foundation; we sometimes
+make exceptions for this.  Our decision will be guided by the two goals
+of preserving the free status of all derivatives of our free software and
+of promoting the sharing and reuse of software generally.
+
+                            NO WARRANTY
+
+  11. BECAUSE THE PROGRAM IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY
+FOR THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE LAW.  EXCEPT WHEN
+OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES
+PROVIDE THE PROGRAM "AS IS" WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED
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+TO THE QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU.  SHOULD THE
+PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING,
+REPAIR OR CORRECTION.
+
+  12. IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING
+WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR
+REDISTRIBUTE THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES,
+INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING
+OUT OF THE USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED
+TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY
+YOU OR THIRD PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER
+PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE
+POSSIBILITY OF SUCH DAMAGES.
+
+                     END OF TERMS AND CONDITIONS
+
+            How to Apply These Terms to Your New Programs
+
+  If you develop a new program, and you want it to be of the greatest
+possible use to the public, the best way to achieve this is to make it
+free software which everyone can redistribute and change under these terms.
+
+  To do so, attach the following notices to the program.  It is safest
+to attach them to the start of each source file to most effectively
+convey the exclusion of warranty; and each file should have at least
+the "copyright" line and a pointer to where the full notice is found.
+
+    <one line to give the program's name and a brief idea of what it does.>
+    Copyright (C) <year>  <name of author>
+
+    This program is free software; you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation; either version 2 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License along
+    with this program; if not, write to the Free Software Foundation, Inc.,
+    51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+
+Also add information on how to contact you by electronic and paper mail.
+
+If the program is interactive, make it output a short notice like this
+when it starts in an interactive mode:
+
+    Gnomovision version 69, Copyright (C) year name of author
+    Gnomovision comes with ABSOLUTELY NO WARRANTY; for details type `show w'.
+    This is free software, and you are welcome to redistribute it
+    under certain conditions; type `show c' for details.
+
+The hypothetical commands `show w' and `show c' should show the appropriate
+parts of the General Public License.  Of course, the commands you use may
+be called something other than `show w' and `show c'; they could even be
+mouse-clicks or menu items--whatever suits your program.
+
+You should also get your employer (if you work as a programmer) or your
+school, if any, to sign a "copyright disclaimer" for the program, if
+necessary.  Here is a sample; alter the names:
+
+  Yoyodyne, Inc., hereby disclaims all copyright interest in the program
+  `Gnomovision' (which makes passes at compilers) written by James Hacker.
+
+  <signature of Ty Coon>, 1 April 1989
+  Ty Coon, President of Vice
+
+This General Public License does not permit incorporating your program into
+proprietary programs.  If your program is a subroutine library, you may
+consider it more useful to permit linking proprietary applications with the
+library.  If this is what you want to do, use the GNU Lesser General
+Public License instead of this License.
diff --git a/us/Makefile b/us/Makefile
new file mode 100644
index 0000000..41b84ea
--- /dev/null
+++ b/us/Makefile
@@ -0,0 +1,2 @@
+all: genltest.c
+	gcc genltest.c $(shell pkg-config --cflags --libs libnl-3.0 libnl-genl-3.0) -o genltest
diff --git a/us/genltest.c b/us/genltest.c
new file mode 100644
index 0000000..caf44f5
--- /dev/null
+++ b/us/genltest.c
@@ -0,0 +1,178 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Generic Netlink libnl example program
+ *
+ * An example on how to use the libnl library for communicating over Generic
+ * Netlink with kernel modules, with unicast and multicast group messages.
+ *
+ *  Copyright (c) 2022 Yaroslav de la Peña Smirnov <yps@yaroslavps.com>
+ */
+#include <stdio.h>
+#include <errno.h>
+#include <signal.h>
+#include <stdbool.h>
+#include <netlink/socket.h>
+#include <netlink/netlink.h>
+#include <netlink/genl/ctrl.h>
+#include <netlink/genl/genl.h>
+#include <netlink/genl/family.h>
+
+#include "../ks/genltest.h"
+
+#define prerr(...) fprintf(stderr, "error: " __VA_ARGS__)
+
+/*
+ * libnl docs and API: https://www.infradead.org/~tgr/libnl/
+ * Current libnl repo: https://github.com/thom311/libnl
+ */
+
+/*
+ * Handler for all received messages from our Generic Netlink family, both
+ * unicast and multicast.
+ */
+static int echo_reply_handler(struct nl_msg *msg, void *arg)
+{
+	int		   err	   = 0;
+	struct genlmsghdr *genlhdr = nlmsg_data(nlmsg_hdr(msg));
+	struct nlattr	  *tb[GENLTEST_A_MAX + 1];
+
+	/* Parse the attributes */
+	err = nla_parse(tb, GENLTEST_A_MAX, genlmsg_attrdata(genlhdr, 0),
+			genlmsg_attrlen(genlhdr, 0), NULL);
+	if (err) {
+		prerr("unable to parse message: %s\n", strerror(-err));
+		return NL_SKIP;
+	}
+	/* Check that there's actually a payload */
+	if (!tb[GENLTEST_A_MSG]) {
+		prerr("msg attribute missing from message\n");
+		return NL_SKIP;
+	}
+
+	/* Print it! */
+	printf("message received: %s\n", nla_get_string(tb[GENLTEST_A_MSG]));
+
+	return NL_OK;
+}
+
+/* Send (unicast) GENLTEST_CMD_ECHO request message */
+static int send_echo_msg(struct nl_sock *sk, int fam)
+{
+	int	       err = 0;
+	struct nl_msg *msg = nlmsg_alloc();
+	if (!msg) {
+		return -ENOMEM;
+	}
+
+	/* Put the genl header inside message buffer */
+	void *hdr = genlmsg_put(msg, NL_AUTO_PORT, NL_AUTO_SEQ, fam, 0, 0,
+				GENLTEST_CMD_ECHO, GENLTEST_GENL_VERSION);
+	if (!hdr) {
+		return -EMSGSIZE;
+	}
+
+	/* Put the string inside the message. */
+	err = nla_put_string(msg, GENLTEST_A_MSG,
+			     "Hello from User Space, Netlink!");
+	if (err < 0) {
+		return -err;
+	}
+	printf("message sent\n");
+
+	/* Send the message. */
+	err = nl_send_auto(sk, msg);
+	err = err >= 0 ? 0 : err;
+
+	nlmsg_free(msg);
+
+	return err;
+}
+
+/* Allocate netlink socket and connect to generic netlink */
+static int conn(struct nl_sock **sk)
+{
+	*sk = nl_socket_alloc();
+	if (!sk) {
+		return -ENOMEM;
+	}
+
+	return genl_connect(*sk);
+}
+
+/* Disconnect and release socket */
+static void disconn(struct nl_sock *sk)
+{
+	nl_close(sk);
+	nl_socket_free(sk);
+}
+
+/* Modify the callback for replies to handle all received messages */
+static inline int set_cb(struct nl_sock *sk)
+{
+	return nl_socket_modify_cb(sk, NL_CB_VALID, NL_CB_CUSTOM,
+				   echo_reply_handler, NULL);
+}
+
+int main(void)
+{
+	int		ret = 1;
+	struct nl_sock *ucsk, *mcsk;
+
+	/*
+	 * We use one socket to receive asynchronous "notifications" over
+	 * multicast group, and another for ops. We do this so that we don't mix
+	 * up responses from ops with notifications to make handling easier.
+	 */
+	if ((ret = conn(&ucsk)) || (ret = conn(&mcsk))) {
+		prerr("failed to connect to generic netlink\n");
+		goto out;
+	}
+
+	/* Resolve the genl family. One family for both unicast and multicast. */
+	int fam = genl_ctrl_resolve(ucsk, GENLTEST_GENL_NAME);
+	if (fam < 0) {
+		prerr("failed to resolve generic netlink family: %s\n",
+		      strerror(-fam));
+		goto out;
+	}
+
+	/* Disable sequence checks for asynchronous multicast messages. */
+	nl_socket_disable_seq_check(mcsk);
+
+	/* Resolve the multicast group. */
+	int mcgrp = genl_ctrl_resolve_grp(mcsk, GENLTEST_GENL_NAME,
+					  GENLTEST_MC_GRP_NAME);
+	if (mcgrp < 0) {
+		prerr("failed to resolve generic netlink multicast group: %s\n",
+		      strerror(-mcgrp));
+		goto out;
+	}
+	/* Join the multicast group. */
+	if ((ret = nl_socket_add_membership(mcsk, mcgrp) < 0)) {
+		prerr("failed to join multicast group: %s\n", strerror(-ret));
+		goto out;
+	}
+
+	if ((ret = set_cb(ucsk)) || (ret = set_cb(mcsk))) {
+		prerr("failed to set callback: %s\n", strerror(-ret));
+		goto out;
+	}
+
+	/* Send unicast message and listen for response. */
+	if ((ret = send_echo_msg(ucsk, fam))) {
+		prerr("failed to send message: %s\n", strerror(-ret));
+	}
+	printf("listening for messages\n");
+	nl_recvmsgs_default(ucsk);
+
+	/* Listen for "notifications". */
+	while (1) {
+		nl_recvmsgs_default(mcsk);
+	}
+
+	ret = 0;
+out:
+	disconn(ucsk);
+	disconn(mcsk);
+	return ret;
+}