selftest: epoll_busy_poll: epoll busy poll tests

Add a simple test for the epoll busy poll ioctls, using the kernel
selftest harness.

This test ensures that the ioctls have the expected return codes and
that the kernel properly gets and sets epoll busy poll parameters.

The test can be expanded in the future to do real busy polling (provided
another machine to act as the client is available).

Signed-off-by: Joe Damato <jdamato@fastly.com>
Link: https://lore.kernel.org/r/20240508184008.48264-1-jdamato@fastly.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

tools/testing/selftests/net/.gitignore

@@ -4,6 +4,7 @@ bind_timewait
 bind_wildcard
 cmsg_sender
 diag_uid
+epoll_busy_poll
 fin_ack_lat
 gro
 hwtstamp_config

tools/testing/selftests/net/Makefile

@@ -67,7 +67,7 @@ TEST_GEN_FILES += ipsec
 TEST_GEN_FILES += ioam6_parser
 TEST_GEN_FILES += gro
 TEST_GEN_PROGS = reuseport_bpf reuseport_bpf_cpu reuseport_bpf_numa
-TEST_GEN_PROGS += reuseport_dualstack reuseaddr_conflict tls tun tap
+TEST_GEN_PROGS += reuseport_dualstack reuseaddr_conflict tls tun tap epoll_busy_poll
 TEST_GEN_FILES += toeplitz
 TEST_GEN_FILES += cmsg_sender
 TEST_GEN_FILES += stress_reuseport_listen
@@ -101,6 +101,7 @@ TEST_INCLUDES := forwarding/lib.sh
 
 include ../lib.mk
 
+$(OUTPUT)/epoll_busy_poll: LDLIBS += -lcap
 $(OUTPUT)/reuseport_bpf_numa: LDLIBS += -lnuma
 $(OUTPUT)/tcp_mmap: LDLIBS += -lpthread -lcrypto
 $(OUTPUT)/tcp_inq: LDLIBS += -lpthread

tools/testing/selftests/net/epoll_busy_poll.c

@@ -0,0 +1,320 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+/* Basic per-epoll context busy poll test.
+ *
+ * Only tests the ioctls, but should be expanded to test two connected hosts in
+ * the future
+ */
+
+#define _GNU_SOURCE
+
+#include <error.h>
+#include <errno.h>
+#include <inttypes.h>
+#include <limits.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+#include <sys/capability.h>
+
+#include <sys/epoll.h>
+#include <sys/ioctl.h>
+#include <sys/socket.h>
+
+#include "../kselftest_harness.h"
+
+/* if the headers haven't been updated, we need to define some things */
+#if !defined(EPOLL_IOC_TYPE)
+struct epoll_params {
+	uint32_t busy_poll_usecs;
+	uint16_t busy_poll_budget;
+	uint8_t prefer_busy_poll;
+
+	/* pad the struct to a multiple of 64bits */
+	uint8_t __pad;
+};
+
+#define EPOLL_IOC_TYPE 0x8A
+#define EPIOCSPARAMS _IOW(EPOLL_IOC_TYPE, 0x01, struct epoll_params)
+#define EPIOCGPARAMS _IOR(EPOLL_IOC_TYPE, 0x02, struct epoll_params)
+#endif
+
+FIXTURE(invalid_fd)
+{
+	int invalid_fd;
+	struct epoll_params params;
+};
+
+FIXTURE_SETUP(invalid_fd)
+{
+	int ret;
+
+	ret = socket(AF_UNIX, SOCK_DGRAM, 0);
+	EXPECT_NE(-1, ret)
+		TH_LOG("error creating unix socket");
+
+	self->invalid_fd = ret;
+}
+
+FIXTURE_TEARDOWN(invalid_fd)
+{
+	int ret;
+
+	ret = close(self->invalid_fd);
+	EXPECT_EQ(0, ret);
+}
+
+TEST_F(invalid_fd, test_invalid_fd)
+{
+	int ret;
+
+	ret = ioctl(self->invalid_fd, EPIOCGPARAMS, &self->params);
+
+	EXPECT_EQ(-1, ret)
+		TH_LOG("EPIOCGPARAMS on invalid epoll FD should error");
+
+	EXPECT_EQ(ENOTTY, errno)
+		TH_LOG("EPIOCGPARAMS on invalid epoll FD should set errno to ENOTTY");
+
+	memset(&self->params, 0, sizeof(struct epoll_params));
+
+	ret = ioctl(self->invalid_fd, EPIOCSPARAMS, &self->params);
+
+	EXPECT_EQ(-1, ret)
+		TH_LOG("EPIOCSPARAMS on invalid epoll FD should error");
+
+	EXPECT_EQ(ENOTTY, errno)
+		TH_LOG("EPIOCSPARAMS on invalid epoll FD should set errno to ENOTTY");
+}
+
+FIXTURE(epoll_busy_poll)
+{
+	int fd;
+	struct epoll_params params;
+	struct epoll_params *invalid_params;
+	cap_t caps;
+};
+
+FIXTURE_SETUP(epoll_busy_poll)
+{
+	int ret;
+
+	ret = epoll_create1(0);
+	EXPECT_NE(-1, ret)
+		TH_LOG("epoll_create1 failed?");
+
+	self->fd = ret;
+
+	self->caps = cap_get_proc();
+	EXPECT_NE(NULL, self->caps);
+}
+
+FIXTURE_TEARDOWN(epoll_busy_poll)
+{
+	int ret;
+
+	ret = close(self->fd);
+	EXPECT_EQ(0, ret);
+
+	ret = cap_free(self->caps);
+	EXPECT_NE(-1, ret)
+		TH_LOG("unable to free capabilities");
+}
+
+TEST_F(epoll_busy_poll, test_get_params)
+{
+	/* begin by getting the epoll params from the kernel
+	 *
+	 * the default should be default and all fields should be zero'd by the
+	 * kernel, so set params fields to garbage to test this.
+	 */
+	int ret = 0;
+
+	self->params.busy_poll_usecs = 0xff;
+	self->params.busy_poll_budget = 0xff;
+	self->params.prefer_busy_poll = 1;
+	self->params.__pad = 0xf;
+
+	ret = ioctl(self->fd, EPIOCGPARAMS, &self->params);
+	EXPECT_EQ(0, ret)
+		TH_LOG("ioctl EPIOCGPARAMS should succeed");
+
+	EXPECT_EQ(0, self->params.busy_poll_usecs)
+		TH_LOG("EPIOCGPARAMS busy_poll_usecs should have been 0");
+
+	EXPECT_EQ(0, self->params.busy_poll_budget)
+		TH_LOG("EPIOCGPARAMS busy_poll_budget should have been 0");
+
+	EXPECT_EQ(0, self->params.prefer_busy_poll)
+		TH_LOG("EPIOCGPARAMS prefer_busy_poll should have been 0");
+
+	EXPECT_EQ(0, self->params.__pad)
+		TH_LOG("EPIOCGPARAMS __pad should have been 0");
+
+	self->invalid_params = (struct epoll_params *)0xdeadbeef;
+	ret = ioctl(self->fd, EPIOCGPARAMS, self->invalid_params);
+
+	EXPECT_EQ(-1, ret)
+		TH_LOG("EPIOCGPARAMS should error with invalid params");
+
+	EXPECT_EQ(EFAULT, errno)
+		TH_LOG("EPIOCGPARAMS with invalid params should set errno to EFAULT");
+}
+
+TEST_F(epoll_busy_poll, test_set_invalid)
+{
+	int ret;
+
+	memset(&self->params, 0, sizeof(struct epoll_params));
+
+	self->params.__pad = 1;
+
+	ret = ioctl(self->fd, EPIOCSPARAMS, &self->params);
+
+	EXPECT_EQ(-1, ret)
+		TH_LOG("EPIOCSPARAMS non-zero __pad should error");
+
+	EXPECT_EQ(EINVAL, errno)
+		TH_LOG("EPIOCSPARAMS non-zero __pad errno should be EINVAL");
+
+	self->params.__pad = 0;
+	self->params.busy_poll_usecs = (uint32_t)INT_MAX + 1;
+
+	ret = ioctl(self->fd, EPIOCSPARAMS, &self->params);
+
+	EXPECT_EQ(-1, ret)
+		TH_LOG("EPIOCSPARAMS should error busy_poll_usecs > S32_MAX");
+
+	EXPECT_EQ(EINVAL, errno)
+		TH_LOG("EPIOCSPARAMS busy_poll_usecs > S32_MAX errno should be EINVAL");
+
+	self->params.__pad = 0;
+	self->params.busy_poll_usecs = 32;
+	self->params.prefer_busy_poll = 2;
+
+	ret = ioctl(self->fd, EPIOCSPARAMS, &self->params);
+
+	EXPECT_EQ(-1, ret)
+		TH_LOG("EPIOCSPARAMS should error prefer_busy_poll > 1");
+
+	EXPECT_EQ(EINVAL, errno)
+		TH_LOG("EPIOCSPARAMS prefer_busy_poll > 1 errno should be EINVAL");
+
+	self->params.__pad = 0;
+	self->params.busy_poll_usecs = 32;
+	self->params.prefer_busy_poll = 1;
+
+	/* set budget well above kernel's NAPI_POLL_WEIGHT of 64 */
+	self->params.busy_poll_budget = UINT16_MAX;
+
+	/* test harness should run with CAP_NET_ADMIN, but let's make sure */
+	cap_flag_value_t tmp;
+
+	ret = cap_get_flag(self->caps, CAP_NET_ADMIN, CAP_EFFECTIVE, &tmp);
+	EXPECT_EQ(0, ret)
+		TH_LOG("unable to get CAP_NET_ADMIN cap flag");
+
+	EXPECT_EQ(CAP_SET, tmp)
+		TH_LOG("expecting CAP_NET_ADMIN to be set for the test harness");
+
+	/* at this point we know CAP_NET_ADMIN is available, so setting the
+	 * params with a busy_poll_budget > NAPI_POLL_WEIGHT should succeed
+	 */
+	ret = ioctl(self->fd, EPIOCSPARAMS, &self->params);
+
+	EXPECT_EQ(0, ret)
+		TH_LOG("EPIOCSPARAMS should allow busy_poll_budget > NAPI_POLL_WEIGHT");
+
+	/* remove CAP_NET_ADMIN from our effective set */
+	cap_value_t net_admin[] = { CAP_NET_ADMIN };
+
+	ret = cap_set_flag(self->caps, CAP_EFFECTIVE, 1, net_admin, CAP_CLEAR);
+	EXPECT_EQ(0, ret)
+		TH_LOG("couldnt clear CAP_NET_ADMIN");
+
+	ret = cap_set_proc(self->caps);
+	EXPECT_EQ(0, ret)
+		TH_LOG("cap_set_proc should drop CAP_NET_ADMIN");
+
+	/* this is now expected to fail */
+	ret = ioctl(self->fd, EPIOCSPARAMS, &self->params);
+
+	EXPECT_EQ(-1, ret)
+		TH_LOG("EPIOCSPARAMS should error busy_poll_budget > NAPI_POLL_WEIGHT");
+
+	EXPECT_EQ(EPERM, errno)
+		TH_LOG("EPIOCSPARAMS errno should be EPERM busy_poll_budget > NAPI_POLL_WEIGHT");
+
+	/* restore CAP_NET_ADMIN to our effective set */
+	ret = cap_set_flag(self->caps, CAP_EFFECTIVE, 1, net_admin, CAP_SET);
+	EXPECT_EQ(0, ret)
+		TH_LOG("couldn't restore CAP_NET_ADMIN");
+
+	ret = cap_set_proc(self->caps);
+	EXPECT_EQ(0, ret)
+		TH_LOG("cap_set_proc should set  CAP_NET_ADMIN");
+
+	self->invalid_params = (struct epoll_params *)0xdeadbeef;
+	ret = ioctl(self->fd, EPIOCSPARAMS, self->invalid_params);
+
+	EXPECT_EQ(-1, ret)
+		TH_LOG("EPIOCSPARAMS should error when epoll_params is invalid");
+
+	EXPECT_EQ(EFAULT, errno)
+		TH_LOG("EPIOCSPARAMS should set errno to EFAULT when epoll_params is invalid");
+}
+
+TEST_F(epoll_busy_poll, test_set_and_get_valid)
+{
+	int ret;
+
+	memset(&self->params, 0, sizeof(struct epoll_params));
+
+	self->params.busy_poll_usecs = 25;
+	self->params.busy_poll_budget = 16;
+	self->params.prefer_busy_poll = 1;
+
+	ret = ioctl(self->fd, EPIOCSPARAMS, &self->params);
+
+	EXPECT_EQ(0, ret)
+		TH_LOG("EPIOCSPARAMS with valid params should not error");
+
+	/* check that the kernel returns the same values back */
+
+	memset(&self->params, 0, sizeof(struct epoll_params));
+
+	ret = ioctl(self->fd, EPIOCGPARAMS, &self->params);
+
+	EXPECT_EQ(0, ret)
+		TH_LOG("EPIOCGPARAMS should not error");
+
+	EXPECT_EQ(25, self->params.busy_poll_usecs)
+		TH_LOG("params.busy_poll_usecs incorrect");
+
+	EXPECT_EQ(16, self->params.busy_poll_budget)
+		TH_LOG("params.busy_poll_budget incorrect");
+
+	EXPECT_EQ(1, self->params.prefer_busy_poll)
+		TH_LOG("params.prefer_busy_poll incorrect");
+
+	EXPECT_EQ(0, self->params.__pad)
+		TH_LOG("params.__pad was not 0");
+}
+
+TEST_F(epoll_busy_poll, test_invalid_ioctl)
+{
+	int invalid_ioctl = EPIOCGPARAMS + 10;
+	int ret;
+
+	ret = ioctl(self->fd, invalid_ioctl, &self->params);
+
+	EXPECT_EQ(-1, ret)
+		TH_LOG("invalid ioctl should return error");
+
+	EXPECT_EQ(EINVAL, errno)
+		TH_LOG("invalid ioctl should set errno to EINVAL");
+}
+
+TEST_HARNESS_MAIN