[PATCH bpf-next 5/7] selftests/bpf: Add netdevsim helper library

@@ -862,6 +862,7 @@ TRUNNER_EXTRA_SOURCES := test_progs.c		\
 			 unpriv_helpers.c 	\
 			 sysctl_helpers.c	\
 			 netlink_helpers.c	\
+			 netdevsim_helpers.c	\
 			 jit_disasm_helpers.c	\
 			 io_helpers.c		\
 			 test_loader.c		\

@@ -0,0 +1,176 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <errno.h>
+#include <fcntl.h>
+#include <linux/rtnetlink.h>
+#include <poll.h>
+#include <stdarg.h>
+#include <stdio.h>
+#include <string.h>
+#include <sys/socket.h>
+#include <time.h>
+#include <unistd.h>
+
+#include "netdevsim_helpers.h"
+
+static int echo(const char *path, const char *fmt, ...)
+{
+	char buf[64];
+	va_list ap;
+	int fd, len, err = 0;
+
+	va_start(ap, fmt);
+	len = vsnprintf(buf, sizeof(buf), fmt, ap);
+	va_end(ap);
+
+	fd = open(path, O_WRONLY);
+	if (fd < 0)
+		return -errno;
+	if (write(fd, buf, len) != len)
+		err = -errno;
+	close(fd);
+
+	return err;
+}
+
+void netdevsim_destroy(unsigned int id)
+{
+	echo("/sys/bus/netdevsim/del_device", "%u", id);
+}
+
+static int create_new_device(void)
+{
+	unsigned int id;
+	int err;
+
+	/* if 10K is not enough, then something is clearly not right */
+	for (id = 0; id < 10000; id++) {
+		err = echo("/sys/bus/netdevsim/new_device", "%u", id);
+		if (!err)
+			return id;
+		if (err != -ENOSPC)
+			return err;
+	}
+
+	return -ENOSPC;
+}
+
+static int open_link_socket(void)
+{
+	struct sockaddr_nl addr = {
+		.nl_family = AF_NETLINK,
+		.nl_groups = RTMGRP_LINK,
+	};
+	int fd;
+
+	fd = socket(AF_NETLINK, SOCK_RAW | SOCK_CLOEXEC, NETLINK_ROUTE);
+	if (fd < 0)
+		return -errno;
+	if (bind(fd, (struct sockaddr *)&addr, sizeof(addr))) {
+		int err = -errno;
+
+		close(fd);
+		return err;
+	}
+
+	return fd;
+}
+
+static int remaining_timeout_ms(const struct timespec *deadline)
+{
+	struct timespec now;
+	long long remaining;
+
+	if (clock_gettime(CLOCK_MONOTONIC, &now))
+		return -errno;
+
+	remaining = (deadline->tv_sec - now.tv_sec) * 1000 +
+		    (deadline->tv_nsec - now.tv_nsec) / 1000000;
+
+	return remaining > 0 ? remaining : 0;
+}
+
+static int recv_device_ifindex(int fd, unsigned int id, unsigned int *ifindex)
+{
+	char parent_name[32], buf[16 * 1024];
+	struct pollfd pfd = {
+		.fd = fd,
+		.events = POLLIN,
+	};
+	struct timespec deadline;
+	struct nlmsghdr *nlh;
+	int len, ret, timeout;
+
+	snprintf(parent_name, sizeof(parent_name), "netdevsim%u", id);
+	if (clock_gettime(CLOCK_MONOTONIC, &deadline))
+		return -errno;
+	deadline.tv_sec += 5;
+
+	for (timeout = remaining_timeout_ms(&deadline); timeout > 0;
+	     timeout = remaining_timeout_ms(&deadline)) {
+		ret = poll(&pfd, 1, timeout);
+		if (ret < 0) {
+			if (errno == EINTR)
+				continue;
+			return -errno;
+		}
+		if (!ret)
+			return -ETIMEDOUT;
+		if (!(pfd.revents & POLLIN))
+			return -EIO;
+
+		len = recv(fd, buf, sizeof(buf), 0);
+		if (len < 0)
+			return -errno;
+
+		for (nlh = (struct nlmsghdr *)buf; NLMSG_OK(nlh, len);
+		     nlh = NLMSG_NEXT(nlh, len)) {
+			struct ifinfomsg *ifm;
+			struct rtattr *attr;
+			int attr_len;
+
+			if (nlh->nlmsg_type != RTM_NEWLINK)
+				continue;
+
+			ifm = NLMSG_DATA(nlh);
+			attr = IFLA_RTA(ifm);
+			attr_len = IFLA_PAYLOAD(nlh);
+			for (; RTA_OK(attr, attr_len);
+			     attr = RTA_NEXT(attr, attr_len)) {
+				if (attr->rta_type != IFLA_PARENT_DEV_NAME)
+					continue;
+				if (strcmp(RTA_DATA(attr), parent_name))
+					continue;
+
+				*ifindex = ifm->ifi_index;
+				return 0;
+			}
+		}
+	}
+
+	return timeout < 0 ? timeout : -ETIMEDOUT;
+}
+
+int netdevsim_create(unsigned int *ifindex)
+{
+	int fd, id, err;
+
+	fd = open_link_socket();
+	if (fd < 0)
+		return fd;
+
+	id = create_new_device();
+	if (id < 0) {
+		close(fd);
+		return id;
+	}
+
+	err = recv_device_ifindex(fd, id, ifindex);
+	close(fd);
+	if (err) {
+		netdevsim_destroy(id);
+		return err;
+	}
+
+	return id;
+}

@@ -0,0 +1,9 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef NETDEVSIM_HELPERS_H
+#define NETDEVSIM_HELPERS_H
+
+int netdevsim_create(unsigned int *ifindex);
+void netdevsim_destroy(unsigned int id);
+
+#endif /* NETDEVSIM_HELPERS_H */