libusb/os/linux_netlink.c - third_party/libusb - Git at Google

 /* -*- Mode: C; c-basic-offset:8 ; indent-tabs-mode:t -*- */
 /*
  * Linux usbfs backend for libusb
  * Copyright (C) 2007-2009 Daniel Drake <dsd@gentoo.org>
  * Copyright (c) 2001 Johannes Erdfelt <johannes@erdfelt.com>
  * Copyright (c) 2013 Nathan Hjelm <hjelmn@mac.com>
  * Copyright (c) 2016 Chris Dickens <christopher.a.dickens@gmail.com>
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public
  * License as published by the Free Software Foundation; either
  * version 2.1 of the License, or (at your option) any later version.
  *
  * This library 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
  * Lesser General Public License for more details.
  *
  * You should have received a copy of the GNU Lesser General Public
  * License along with this library; if not, write to the Free Software
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  */

 #include "libusbi.h"
 #include "linux_usbfs.h"

 #include <errno.h>
 #include <fcntl.h>
 #include <poll.h>
 #include <pthread.h>
 #include <string.h>
 #include <unistd.h>

 #ifdef HAVE_ASM_TYPES_H
 #include <asm/types.h>
 #endif
 #include <sys/socket.h>
 #include <linux/netlink.h>

 #define NL_GROUP_KERNEL 1

 #ifndef SOCK_CLOEXEC
 #define SOCK_CLOEXEC	0
 #endif

 #ifndef SOCK_NONBLOCK
 #define SOCK_NONBLOCK	0
 #endif

 static int linux_netlink_socket = -1;
 static usbi_event_t netlink_control_event = USBI_INVALID_EVENT;
 static pthread_t libusb_linux_event_thread;

 static void *linux_netlink_event_thread_main(void *arg);

 static int set_fd_cloexec_nb(int fd, int socktype)
 {
 	int flags;

 #if defined(FD_CLOEXEC)
 	/* Make sure the netlink socket file descriptor is marked as CLOEXEC */
 	if (!(socktype & SOCK_CLOEXEC)) {
 		flags = fcntl(fd, F_GETFD);
 		if (flags == -1) {
 			usbi_err(NULL, "failed to get netlink fd flags, errno=%d", errno);
 			return -1;
 		}

 		if (fcntl(fd, F_SETFD, flags | FD_CLOEXEC) == -1) {
 			usbi_err(NULL, "failed to set netlink fd flags, errno=%d", errno);
 			return -1;
 		}
 	}
 #endif

 	/* Make sure the netlink socket is non-blocking */
 	if (!(socktype & SOCK_NONBLOCK)) {
 		flags = fcntl(fd, F_GETFL);
 		if (flags == -1) {
 			usbi_err(NULL, "failed to get netlink fd status flags, errno=%d", errno);
 			return -1;
 		}

 		if (fcntl(fd, F_SETFL, flags | O_NONBLOCK) == -1) {
 			usbi_err(NULL, "failed to set netlink fd status flags, errno=%d", errno);
 			return -1;
 		}
 	}

 	return 0;
 }

 int linux_netlink_start_event_monitor(void)
 {
 	struct sockaddr_nl sa_nl = { .nl_family = AF_NETLINK, .nl_groups = NL_GROUP_KERNEL };
 	int socktype = SOCK_RAW | SOCK_NONBLOCK | SOCK_CLOEXEC;
 	int opt = 1;
 	int ret;

 	linux_netlink_socket = socket(PF_NETLINK, socktype, NETLINK_KOBJECT_UEVENT);
 	if (linux_netlink_socket == -1 && errno == EINVAL) {
 		usbi_dbg(NULL, "failed to create netlink socket of type %d, attempting SOCK_RAW", socktype);
 		socktype = SOCK_RAW;
 		linux_netlink_socket = socket(PF_NETLINK, socktype, NETLINK_KOBJECT_UEVENT);
 	}

 	if (linux_netlink_socket == -1) {
 		usbi_err(NULL, "failed to create netlink socket, errno=%d", errno);
 		goto err;
 	}

 	ret = set_fd_cloexec_nb(linux_netlink_socket, socktype);
 	if (ret == -1)
 		goto err_close_socket;

 	ret = bind(linux_netlink_socket, (struct sockaddr *)&sa_nl, sizeof(sa_nl));
 	if (ret == -1) {
 		usbi_err(NULL, "failed to bind netlink socket, errno=%d", errno);
 		goto err_close_socket;
 	}

 	ret = setsockopt(linux_netlink_socket, SOL_SOCKET, SO_PASSCRED, &opt, sizeof(opt));
 	if (ret == -1) {
 		usbi_err(NULL, "failed to set netlink socket SO_PASSCRED option, errno=%d", errno);
 		goto err_close_socket;
 	}

 	ret = usbi_create_event(&netlink_control_event);
 	if (ret) {
 		usbi_err(NULL, "failed to create netlink control event");
 		goto err_close_socket;
 	}

 	ret = pthread_create(&libusb_linux_event_thread, NULL, linux_netlink_event_thread_main, NULL);
 	if (ret != 0) {
 		usbi_err(NULL, "failed to create netlink event thread (%d)", ret);
 		goto err_destroy_event;
 	}

 	return LIBUSB_SUCCESS;

 err_destroy_event:
 	usbi_destroy_event(&netlink_control_event);
 	netlink_control_event = (usbi_event_t)USBI_INVALID_EVENT;
 err_close_socket:
 	close(linux_netlink_socket);
 	linux_netlink_socket = -1;
 err:
 	return LIBUSB_ERROR_OTHER;
 }

 int linux_netlink_stop_event_monitor(void)
 {
 	int ret;

 	assert(linux_netlink_socket != -1);

 	/* Signal the control event and wait for the thread to exit */
 	usbi_signal_event(&netlink_control_event);

 	ret = pthread_join(libusb_linux_event_thread, NULL);
 	if (ret)
 		usbi_warn(NULL, "failed to join netlink event thread (%d)", ret);

 	usbi_destroy_event(&netlink_control_event);
 	netlink_control_event = (usbi_event_t)USBI_INVALID_EVENT;

 	close(linux_netlink_socket);
 	linux_netlink_socket = -1;

 	return LIBUSB_SUCCESS;
 }

 static const char *netlink_message_parse(const char *buffer, size_t len, const char *key)
 {
 	const char *end = buffer + len;
 	size_t keylen = strlen(key);

 	while (buffer < end && *buffer) {
 		if (strncmp(buffer, key, keylen) == 0 && buffer[keylen] == '=')
 			return buffer + keylen + 1;
 		buffer += strlen(buffer) + 1;
 	}

 	return NULL;
 }

 /* parse parts of netlink message common to both libudev and the kernel */
 static int linux_netlink_parse(const char *buffer, size_t len, int *detached,
 	const char **sys_name, uint8_t *busnum, uint8_t *devaddr)
 {
 	const char *tmp, *slash;

 	errno = 0;

 	*sys_name = NULL;
 	*detached = 0;
 	*busnum   = 0;
 	*devaddr  = 0;

 	tmp = netlink_message_parse(buffer, len, "ACTION");
 	if (!tmp) {
 		return -1;
 	} else if (strcmp(tmp, "remove") == 0) {
 		*detached = 1;
 	} else if (strcmp(tmp, "add") != 0) {
 		usbi_dbg(NULL, "unknown device action %s", tmp);
 		return -1;
 	}

 	/* check that this is a usb message */
 	tmp = netlink_message_parse(buffer, len, "SUBSYSTEM");
 	if (!tmp || strcmp(tmp, "usb") != 0) {
 		/* not usb. ignore */
 		return -1;
 	}

 	/* check that this is an actual usb device */
 	tmp = netlink_message_parse(buffer, len, "DEVTYPE");
 	if (!tmp || strcmp(tmp, "usb_device") != 0) {
 		/* not usb. ignore */
 		return -1;
 	}

 	tmp = netlink_message_parse(buffer, len, "BUSNUM");
 	if (tmp) {
 		*busnum = (uint8_t)(strtoul(tmp, NULL, 10) & 0xff);
 		if (errno) {
 			errno = 0;
 			return -1;
 		}

 		tmp = netlink_message_parse(buffer, len, "DEVNUM");
 		if (NULL == tmp)
 			return -1;

 		*devaddr = (uint8_t)(strtoul(tmp, NULL, 10) & 0xff);
 		if (errno) {
 			errno = 0;
 			return -1;
 		}
 	} else {
 		/* no bus number. try "DEVICE" */
 		tmp = netlink_message_parse(buffer, len, "DEVICE");
 		if (!tmp) {
 			/* not usb. ignore */
 			return -1;
 		}

 		/* Parse a device path such as /dev/bus/usb/003/004 */
 		slash = strrchr(tmp, '/');
 		if (!slash)
 			return -1;

 		*busnum = (uint8_t)(strtoul(slash - 3, NULL, 10) & 0xff);
 		if (errno) {
 			errno = 0;
 			return -1;
 		}

 		*devaddr = (uint8_t)(strtoul(slash + 1, NULL, 10) & 0xff);
 		if (errno) {
 			errno = 0;
 			return -1;
 		}

 		return 0;
 	}

 	tmp = netlink_message_parse(buffer, len, "DEVPATH");
 	if (!tmp)
 		return -1;

 	slash = strrchr(tmp, '/');
 	if (slash)
 		*sys_name = slash + 1;

 	/* found a usb device */
 	return 0;
 }

 static int linux_netlink_read_message(void)
 {
 	char cred_buffer[CMSG_SPACE(sizeof(struct ucred))];
 	char msg_buffer[2048];
 	const char *sys_name = NULL;
 	uint8_t busnum, devaddr;
 	int detached, r;
 	ssize_t len;
 	struct cmsghdr *cmsg;
 	struct ucred *cred;
 	struct sockaddr_nl sa_nl;
 	struct iovec iov = { .iov_base = msg_buffer, .iov_len = sizeof(msg_buffer) };
 	struct msghdr msg = {
 		.msg_iov = &iov, .msg_iovlen = 1,
 		.msg_control = cred_buffer, .msg_controllen = sizeof(cred_buffer),
 		.msg_name = &sa_nl, .msg_namelen = sizeof(sa_nl)
 	};

 	/* read netlink message */
 	len = recvmsg(linux_netlink_socket, &msg, 0);
 	if (len == -1) {
 		if (errno != EAGAIN && errno != EINTR)
 			usbi_err(NULL, "error receiving message from netlink, errno=%d", errno);
 		return -1;
 	}

 	if (len < 32 || (msg.msg_flags & MSG_TRUNC)) {
 		usbi_err(NULL, "invalid netlink message length");
 		return -1;
 	}

 	if (sa_nl.nl_groups != NL_GROUP_KERNEL || sa_nl.nl_pid != 0) {
 		usbi_dbg(NULL, "ignoring netlink message from unknown group/PID (%u/%u)",
 			 (unsigned int)sa_nl.nl_groups, (unsigned int)sa_nl.nl_pid);
 		return -1;
 	}

 	cmsg = CMSG_FIRSTHDR(&msg);
 	if (!cmsg || cmsg->cmsg_type != SCM_CREDENTIALS) {
 		usbi_dbg(NULL, "ignoring netlink message with no sender credentials");
 		return -1;
 	}

 	cred = (struct ucred *)CMSG_DATA(cmsg);
 	if (cred->uid != 0) {
 		usbi_dbg(NULL, "ignoring netlink message with non-zero sender UID %u", (unsigned int)cred->uid);
 		return -1;
 	}

 	r = linux_netlink_parse(msg_buffer, (size_t)len, &detached, &sys_name, &busnum, &devaddr);
 	if (r)
 		return r;

 	usbi_dbg(NULL, "netlink hotplug found device busnum: %hhu, devaddr: %hhu, sys_name: %s, removed: %s",
 		 busnum, devaddr, sys_name, detached ? "yes" : "no");

 	/* signal device is available (or not) to all contexts */
 	if (detached)
 		linux_device_disconnected(busnum, devaddr);
 	else
 		linux_hotplug_enumerate(busnum, devaddr, sys_name);

 	return 0;
 }

 static void *linux_netlink_event_thread_main(void *arg)
 {
 	struct pollfd fds[] = {
 		{ .fd = USBI_EVENT_OS_HANDLE(&netlink_control_event),
 		  .events = USBI_EVENT_POLL_EVENTS },
 		{ .fd = linux_netlink_socket,
 		  .events = POLLIN },
 	};
 	int r;

 	UNUSED(arg);

 #if defined(HAVE_PTHREAD_SETNAME_NP)
 	r = pthread_setname_np(pthread_self(), "libusb_event");
 	if (r)
 		usbi_warn(NULL, "failed to set hotplug event thread name, error=%d", r);
 #endif

 	usbi_dbg(NULL, "netlink event thread entering");

 	while (1) {
 		r = poll(fds, 2, -1);
 		if (r == -1) {
 			/* check for temporary failure */
 			if (errno == EINTR)
 				continue;
 			usbi_err(NULL, "poll() failed, errno=%d", errno);
 			break;
 		}
 		if (fds[0].revents) {
 			/* activity on control event, exit */
 			break;
 		}
 		if (fds[1].revents) {
 			usbi_mutex_static_lock(&linux_hotplug_lock);
 			linux_netlink_read_message();
 			usbi_mutex_static_unlock(&linux_hotplug_lock);
 		}
 	}

 	usbi_dbg(NULL, "netlink event thread exiting");

 	return NULL;
 }

 void linux_netlink_hotplug_poll(void)
 {
 	int r;

 	usbi_mutex_static_lock(&linux_hotplug_lock);
 	do {
 		r = linux_netlink_read_message();
 	} while (r == 0);
 	usbi_mutex_static_unlock(&linux_hotplug_lock);
 }
	/* -- Mode: C; c-basic-offset:8 ; indent-tabs-mode:t -- */
	/*
	* Linux usbfs backend for libusb
	* Copyright (C) 2007-2009 Daniel Drake <dsd@gentoo.org>
	* Copyright (c) 2001 Johannes Erdfelt <johannes@erdfelt.com>
	* Copyright (c) 2013 Nathan Hjelm <hjelmn@mac.com>
	* Copyright (c) 2016 Chris Dickens <christopher.a.dickens@gmail.com>
	*
	* This library is free software; you can redistribute it and/or
	* modify it under the terms of the GNU Lesser General Public
	* License as published by the Free Software Foundation; either
	* version 2.1 of the License, or (at your option) any later version.
	*
	* This library 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
	* Lesser General Public License for more details.
	*
	* You should have received a copy of the GNU Lesser General Public
	* License along with this library; if not, write to the Free Software
	* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
	*/

	#include "libusbi.h"
	#include "linux_usbfs.h"

	#include <errno.h>
	#include <fcntl.h>
	#include <poll.h>
	#include <pthread.h>
	#include <string.h>
	#include <unistd.h>

	#ifdef HAVE_ASM_TYPES_H
	#include <asm/types.h>
	#endif
	#include <sys/socket.h>
	#include <linux/netlink.h>

	#define NL_GROUP_KERNEL 1

	#ifndef SOCK_CLOEXEC
	#define SOCK_CLOEXEC 0
	#endif

	#ifndef SOCK_NONBLOCK
	#define SOCK_NONBLOCK 0
	#endif

	static int linux_netlink_socket = -1;
	static usbi_event_t netlink_control_event = USBI_INVALID_EVENT;
	static pthread_t libusb_linux_event_thread;

	static void linux_netlink_event_thread_main(void arg);

	static int set_fd_cloexec_nb(int fd, int socktype)
	{
	int flags;

	#if defined(FD_CLOEXEC)
	/* Make sure the netlink socket file descriptor is marked as CLOEXEC */
	if (!(socktype & SOCK_CLOEXEC)) {
	flags = fcntl(fd, F_GETFD);
	if (flags == -1) {
	usbi_err(NULL, "failed to get netlink fd flags, errno=%d", errno);
	return -1;
	}

	if (fcntl(fd, F_SETFD, flags \| FD_CLOEXEC) == -1) {
	usbi_err(NULL, "failed to set netlink fd flags, errno=%d", errno);
	return -1;
	}
	}
	#endif

	/* Make sure the netlink socket is non-blocking */
	if (!(socktype & SOCK_NONBLOCK)) {
	flags = fcntl(fd, F_GETFL);
	if (flags == -1) {
	usbi_err(NULL, "failed to get netlink fd status flags, errno=%d", errno);
	return -1;
	}

	if (fcntl(fd, F_SETFL, flags \| O_NONBLOCK) == -1) {
	usbi_err(NULL, "failed to set netlink fd status flags, errno=%d", errno);
	return -1;
	}
	}

	return 0;
	}

	int linux_netlink_start_event_monitor(void)
	{
	struct sockaddr_nl sa_nl = { .nl_family = AF_NETLINK, .nl_groups = NL_GROUP_KERNEL };
	int socktype = SOCK_RAW \| SOCK_NONBLOCK \| SOCK_CLOEXEC;
	int opt = 1;
	int ret;

	linux_netlink_socket = socket(PF_NETLINK, socktype, NETLINK_KOBJECT_UEVENT);
	if (linux_netlink_socket == -1 && errno == EINVAL) {
	usbi_dbg(NULL, "failed to create netlink socket of type %d, attempting SOCK_RAW", socktype);
	socktype = SOCK_RAW;
	linux_netlink_socket = socket(PF_NETLINK, socktype, NETLINK_KOBJECT_UEVENT);
	}

	if (linux_netlink_socket == -1) {
	usbi_err(NULL, "failed to create netlink socket, errno=%d", errno);
	goto err;
	}

	ret = set_fd_cloexec_nb(linux_netlink_socket, socktype);
	if (ret == -1)
	goto err_close_socket;

	ret = bind(linux_netlink_socket, (struct sockaddr *)&sa_nl, sizeof(sa_nl));
	if (ret == -1) {
	usbi_err(NULL, "failed to bind netlink socket, errno=%d", errno);
	goto err_close_socket;
	}

	ret = setsockopt(linux_netlink_socket, SOL_SOCKET, SO_PASSCRED, &opt, sizeof(opt));
	if (ret == -1) {
	usbi_err(NULL, "failed to set netlink socket SO_PASSCRED option, errno=%d", errno);
	goto err_close_socket;
	}

	ret = usbi_create_event(&netlink_control_event);
	if (ret) {
	usbi_err(NULL, "failed to create netlink control event");
	goto err_close_socket;
	}

	ret = pthread_create(&libusb_linux_event_thread, NULL, linux_netlink_event_thread_main, NULL);
	if (ret != 0) {
	usbi_err(NULL, "failed to create netlink event thread (%d)", ret);
	goto err_destroy_event;
	}

	return LIBUSB_SUCCESS;

	err_destroy_event:
	usbi_destroy_event(&netlink_control_event);
	netlink_control_event = (usbi_event_t)USBI_INVALID_EVENT;
	err_close_socket:
	close(linux_netlink_socket);
	linux_netlink_socket = -1;
	err:
	return LIBUSB_ERROR_OTHER;
	}

	int linux_netlink_stop_event_monitor(void)
	{
	int ret;

	assert(linux_netlink_socket != -1);

	/* Signal the control event and wait for the thread to exit */
	usbi_signal_event(&netlink_control_event);

	ret = pthread_join(libusb_linux_event_thread, NULL);
	if (ret)
	usbi_warn(NULL, "failed to join netlink event thread (%d)", ret);

	usbi_destroy_event(&netlink_control_event);
	netlink_control_event = (usbi_event_t)USBI_INVALID_EVENT;

	close(linux_netlink_socket);
	linux_netlink_socket = -1;

	return LIBUSB_SUCCESS;
	}

	static const char netlink_message_parse(const char buffer, size_t len, const char *key)
	{
	const char *end = buffer + len;
	size_t keylen = strlen(key);

	while (buffer < end && *buffer) {
	if (strncmp(buffer, key, keylen) == 0 && buffer[keylen] == '=')
	return buffer + keylen + 1;
	buffer += strlen(buffer) + 1;
	}

	return NULL;
	}

	/* parse parts of netlink message common to both libudev and the kernel */
	static int linux_netlink_parse(const char buffer, size_t len, int detached,
	const char *sys_name, uint8_t busnum, uint8_t *devaddr)
	{
	const char tmp, slash;

	errno = 0;

	*sys_name = NULL;
	*detached = 0;
	*busnum = 0;
	*devaddr = 0;

	tmp = netlink_message_parse(buffer, len, "ACTION");
	if (!tmp) {
	return -1;
	} else if (strcmp(tmp, "remove") == 0) {
	*detached = 1;
	} else if (strcmp(tmp, "add") != 0) {
	usbi_dbg(NULL, "unknown device action %s", tmp);
	return -1;
	}

	/* check that this is a usb message */
	tmp = netlink_message_parse(buffer, len, "SUBSYSTEM");
	if (!tmp \|\| strcmp(tmp, "usb") != 0) {
	/* not usb. ignore */
	return -1;
	}

	/* check that this is an actual usb device */
	tmp = netlink_message_parse(buffer, len, "DEVTYPE");
	if (!tmp \|\| strcmp(tmp, "usb_device") != 0) {
	/* not usb. ignore */
	return -1;
	}

	tmp = netlink_message_parse(buffer, len, "BUSNUM");
	if (tmp) {
	*busnum = (uint8_t)(strtoul(tmp, NULL, 10) & 0xff);
	if (errno) {
	errno = 0;
	return -1;
	}

	tmp = netlink_message_parse(buffer, len, "DEVNUM");
	if (NULL == tmp)
	return -1;

	*devaddr = (uint8_t)(strtoul(tmp, NULL, 10) & 0xff);
	if (errno) {
	errno = 0;
	return -1;
	}
	} else {
	/* no bus number. try "DEVICE" */
	tmp = netlink_message_parse(buffer, len, "DEVICE");
	if (!tmp) {
	/* not usb. ignore */
	return -1;
	}

	/* Parse a device path such as /dev/bus/usb/003/004 */
	slash = strrchr(tmp, '/');
	if (!slash)
	return -1;

	*busnum = (uint8_t)(strtoul(slash - 3, NULL, 10) & 0xff);
	if (errno) {
	errno = 0;
	return -1;
	}

	*devaddr = (uint8_t)(strtoul(slash + 1, NULL, 10) & 0xff);
	if (errno) {
	errno = 0;
	return -1;
	}

	return 0;
	}

	tmp = netlink_message_parse(buffer, len, "DEVPATH");
	if (!tmp)
	return -1;

	slash = strrchr(tmp, '/');
	if (slash)
	*sys_name = slash + 1;

	/* found a usb device */
	return 0;
	}

	static int linux_netlink_read_message(void)
	{
	char cred_buffer[CMSG_SPACE(sizeof(struct ucred))];
	char msg_buffer[2048];
	const char *sys_name = NULL;
	uint8_t busnum, devaddr;
	int detached, r;
	ssize_t len;
	struct cmsghdr *cmsg;
	struct ucred *cred;
	struct sockaddr_nl sa_nl;
	struct iovec iov = { .iov_base = msg_buffer, .iov_len = sizeof(msg_buffer) };
	struct msghdr msg = {
	.msg_iov = &iov, .msg_iovlen = 1,
	.msg_control = cred_buffer, .msg_controllen = sizeof(cred_buffer),
	.msg_name = &sa_nl, .msg_namelen = sizeof(sa_nl)
	};

	/* read netlink message */
	len = recvmsg(linux_netlink_socket, &msg, 0);
	if (len == -1) {
	if (errno != EAGAIN && errno != EINTR)
	usbi_err(NULL, "error receiving message from netlink, errno=%d", errno);
	return -1;
	}

	if (len < 32 \|\| (msg.msg_flags & MSG_TRUNC)) {
	usbi_err(NULL, "invalid netlink message length");
	return -1;
	}

	if (sa_nl.nl_groups != NL_GROUP_KERNEL \|\| sa_nl.nl_pid != 0) {
	usbi_dbg(NULL, "ignoring netlink message from unknown group/PID (%u/%u)",
	(unsigned int)sa_nl.nl_groups, (unsigned int)sa_nl.nl_pid);
	return -1;
	}

	cmsg = CMSG_FIRSTHDR(&msg);
	if (!cmsg \|\| cmsg->cmsg_type != SCM_CREDENTIALS) {
	usbi_dbg(NULL, "ignoring netlink message with no sender credentials");
	return -1;
	}

	cred = (struct ucred *)CMSG_DATA(cmsg);
	if (cred->uid != 0) {
	usbi_dbg(NULL, "ignoring netlink message with non-zero sender UID %u", (unsigned int)cred->uid);
	return -1;
	}

	r = linux_netlink_parse(msg_buffer, (size_t)len, &detached, &sys_name, &busnum, &devaddr);
	if (r)
	return r;

	usbi_dbg(NULL, "netlink hotplug found device busnum: %hhu, devaddr: %hhu, sys_name: %s, removed: %s",
	busnum, devaddr, sys_name, detached ? "yes" : "no");

	/* signal device is available (or not) to all contexts */
	if (detached)
	linux_device_disconnected(busnum, devaddr);
	else
	linux_hotplug_enumerate(busnum, devaddr, sys_name);

	return 0;
	}

	static void linux_netlink_event_thread_main(void arg)
	{
	struct pollfd fds[] = {
	{ .fd = USBI_EVENT_OS_HANDLE(&netlink_control_event),
	.events = USBI_EVENT_POLL_EVENTS },
	{ .fd = linux_netlink_socket,
	.events = POLLIN },
	};
	int r;

	UNUSED(arg);

	#if defined(HAVE_PTHREAD_SETNAME_NP)
	r = pthread_setname_np(pthread_self(), "libusb_event");
	if (r)
	usbi_warn(NULL, "failed to set hotplug event thread name, error=%d", r);
	#endif

	usbi_dbg(NULL, "netlink event thread entering");

	while (1) {
	r = poll(fds, 2, -1);
	if (r == -1) {
	/* check for temporary failure */
	if (errno == EINTR)
	continue;
	usbi_err(NULL, "poll() failed, errno=%d", errno);
	break;
	}
	if (fds[0].revents) {
	/* activity on control event, exit */
	break;
	}
	if (fds[1].revents) {
	usbi_mutex_static_lock(&linux_hotplug_lock);
	linux_netlink_read_message();
	usbi_mutex_static_unlock(&linux_hotplug_lock);
	}
	}

	usbi_dbg(NULL, "netlink event thread exiting");

	return NULL;
	}

	void linux_netlink_hotplug_poll(void)
	{
	int r;

	usbi_mutex_static_lock(&linux_hotplug_lock);
	do {
	r = linux_netlink_read_message();
	} while (r == 0);
	usbi_mutex_static_unlock(&linux_hotplug_lock);
	}