Subject: Re: [PATCH net-next v3] selftest: epoll_busy_poll: epoll busy poll tests

From: Joe Damato <[email-masked]>
Date: Tue, 7 May 2024 19:21:50 -0700

On Wed, May 08, 2024 at 12:43:26AM +0000, Joe Damato wrote:
> 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).

Ah, built and worked for me, but of course fails remotely:

epoll_busy_poll.c:20:10: fatal error: sys/capability.h: No such file or directory
   20 | #include <sys/capability.h>
      |          ^~~~~~~~~~~~~~~~~~

Looks like selftests/bpf/cap_helpers.c avoids a similar-ish issue? Not sure if
there's a better way or if I should do something like that?

I assume it is not possible to add deps like libcap-dev to the test harness somehow?

> Signed-off-by: Joe Damato <[email-masked]>
> ---
> v2 -> v3:
>   - Added this changelog :)
>   - Add libcap to LDLIBS.
>   - Most other changes are in test_set_invalid:
>     - Check if CAP_NET_ADMIN is set in the effective set before setting
>       busy_poll_budget over NAPI_POLL_WEIGHT. The test which follows
>       assumes CAP_NET_ADMIN.
>     - Drop CAP_NET_ADMIN from effective set in order to ensure the ioctl
>       fails when busy_poll_budget exceeds NAPI_POLL_WEIGHT.
>     - Put CAP_NET_ADMIN back into the effective set afterwards.
>     - Changed self->params.busy_poll_budget from 65535 to UINT16_MAX.
>     - Changed the cast for params.busy_poll_usecs from unsigned int to
>       uint32_t in the test_set_invalid case.
> 
> v1 -> v2:
>   - Rewrote completely to use kernel self test harness.
> 
>  tools/testing/selftests/net/.gitignore        |   1 +
>  tools/testing/selftests/net/Makefile          |   3 +-
>  tools/testing/selftests/net/epoll_busy_poll.c | 320 ++++++++++++++++++
>  3 files changed, 323 insertions(+), 1 deletion(-)
>  create mode 100644 tools/testing/selftests/net/epoll_busy_poll.c
> 
> diff --git a/tools/testing/selftests/net/.gitignore b/tools/testing/selftests/net/.gitignore
> index d996a0ab0765..777cfd027076 100644
> --- a/tools/testing/selftests/net/.gitignore
> +++ b/tools/testing/selftests/net/.gitignore
> @@ -5,6 +5,7 @@ bind_wildcard
>  csum
>  cmsg_sender
>  diag_uid
> +epoll_busy_poll
>  fin_ack_lat
>  gro
>  hwtstamp_config
> diff --git a/tools/testing/selftests/net/Makefile b/tools/testing/selftests/net/Makefile
> index 5befca249452..c6112d08b233 100644
> --- a/tools/testing/selftests/net/Makefile
> +++ b/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
> @@ -102,6 +102,7 @@ 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
> diff --git a/tools/testing/selftests/net/epoll_busy_poll.c b/tools/testing/selftests/net/epoll_busy_poll.c
> new file mode 100644
> index 000000000000..9dd2830fd67c
> --- /dev/null
> +++ b/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
> -- 
> 2.25.1
>