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authorYaroslav de la Peña Smirnov <yps@yaroslavps.com>2023-02-11 01:51:36 +0300
committerYaroslav de la Peña Smirnov <yps@yaroslavps.com>2023-02-11 01:51:36 +0300
commit017598b41e59aa0bdb121020c29746cd062cdec0 (patch)
treeac4227f670146feae286fa9afb0d6dbd2f41dbea
downloadgenltest-master.tar.gz
genltest-master.zip
-rw-r--r--.gitignore10
-rw-r--r--README.md30
-rw-r--r--ks/.exrc4
-rw-r--r--ks/COPYING7
-rw-r--r--ks/LICENSE339
-rw-r--r--ks/Makefile11
-rw-r--r--ks/genltest.c215
-rw-r--r--ks/genltest.h31
-rw-r--r--us/.exrc3
-rw-r--r--us/COPYING7
-rw-r--r--us/LICENSE339
-rw-r--r--us/Makefile2
-rw-r--r--us/genltest.c178
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
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+Foundation's software and to any other program whose authors commit to
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+ When we speak of free software, we are referring to freedom, not
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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
+program will individually obtain patent licenses, in effect making the
+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
+ announcement including an appropriate copyright notice and a
+ 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
+ does not normally print such an announcement, your work based on
+ 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
+ 1 and 2 above on a medium customarily used for software interchange; or,
+
+ 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
+ cost of physically performing source distribution, a complete
+ machine-readable copy of the corresponding source code, to be
+ distributed under the terms of Sections 1 and 2 above on a medium
+ customarily used for software interchange; or,
+
+ 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
+making modifications to it. For an executable work, complete source
+code means all the source code for all modules it contains, plus any
+associated interface definition files, plus the scripts used to
+control compilation and installation of the executable. However, as a
+special exception, the source code distributed need not include
+anything that is normally distributed (in either source or binary
+form) with the major components (compiler, kernel, and so on) of the
+operating system on which the executable runs, unless that component
+itself accompanies the executable.
+
+If distribution of executable or object code is made by offering
+access to copy from a designated place, then offering equivalent
+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
+otherwise) that contradict the conditions of this License, they do not
+excuse you from the conditions of this License. If you cannot
+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
+circumstances.
+
+It is not the purpose of this section to induce you to infringe any
+patents or other property right claims or to contest validity of any
+such claims; this section has the sole purpose of protecting the
+integrity of the free software distribution system, which is
+implemented by public license practices. Many people have made
+generous contributions to the wide range of software distributed
+through that system in reliance on consistent application of that
+system; it is up to the author/donor to decide if he or she is willing
+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
+OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
+MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE ENTIRE RISK AS
+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;
+}