hotplug-netlink: sample program from kernel docs

utils/hotplug-netlink/Makefile

@@ -0,0 +1,34 @@
+#
+# Copyright (C) 2016 OpenWrt.org
+#
+# This is free software, licensed under the GNU General Public License v2.
+# See /LICENSE for more information.
+#
+
+include $(TOPDIR)/rules.mk
+
+PKG_NAME:=hotplug-netlink
+PKG_RELEASE:=1
+PKG_MAINTAINER:=Karl Palsson <karlp@etactica.com>
+
+PKG_BUILD_DIR := $(BUILD_DIR)/$(PKG_NAME)
+
+include $(INCLUDE_DIR)/package.mk
+
+define Package/$(PKG_NAME)
+  SECTION:=utils
+  CATEGORY:=Utilities
+  TITLE:=hotplug netlink debugger
+  DEPENDS:=+libc
+endef
+
+define Build/Prepare
+	$(CP) ./files/* $(PKG_BUILD_DIR)/
+endef
+
+define Package/$(PKG_NAME)/install
+	$(INSTALL_DIR) $(1)/usr/bin
+	$(INSTALL_BIN) $(PKG_BUILD_DIR)/dbg-hotplug-netlink $(1)/usr/bin
+endef
+
+$(eval $(call BuildPackage,$(PKG_NAME)))

utils/hotplug-netlink/files/Makefile

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+APP=dbg-hotplug-netlink
+
+all: $(APP)
+
+clean:
+	$(RM) $(APP)

utils/hotplug-netlink/files/dbg-hotplug-netlink.c

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+/*
+ * From https://www.kernel.org/doc/pending/hotplug.txt
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include <sys/poll.h>
+#include <sys/socket.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+#include <linux/types.h>
+#include <linux/netlink.h>
+
+void die(char *s)
+{
+	write(2, s, strlen(s));
+	exit(1);
+}
+
+int main(int argc, char *argv[])
+{
+	struct sockaddr_nl nls;
+	struct pollfd pfd;
+	char buf[512];
+
+	// Open hotplug event netlink socket
+
+	memset(&nls, 0, sizeof(struct sockaddr_nl));
+	nls.nl_family = AF_NETLINK;
+	nls.nl_pid = getpid();
+	nls.nl_groups = -1;
+
+	pfd.events = POLLIN;
+	pfd.fd = socket(PF_NETLINK, SOCK_DGRAM, NETLINK_KOBJECT_UEVENT);
+	if (pfd.fd == -1)
+		die("Not root\n");
+
+	// Listen to netlink socket
+
+	if (bind(pfd.fd, (void *) &nls, sizeof(struct sockaddr_nl)))
+		die("Bind failed\n");
+	while (-1 != poll(&pfd, 1, -1)) {
+		int i, len = recv(pfd.fd, buf, sizeof(buf), MSG_DONTWAIT);
+		if (len == -1) die("recv\n");
+
+		// Print the data to stdout.
+		i = 0;
+		while (i < len) {
+			printf("%s\n", buf + i);
+			i += strlen(buf + i) + 1;
+		}
+	}
+	die("poll\n");
+
+	// Dear gcc: shut up.
+	return 0;
+}