[Devel] [PATCH hci-8.1 v3 1/1] selftests/bpf: run the xsk veth tests in a network namespace of their own

[Eva Kurchatova <eva.kurchatova@virtuozzo.com>]

test_xsk.sh makes its veth pair in the namespace it runs in. Whatever
the host does with a new interface, address configuration, neighbour
discovery, happens on that pair, and the AF_XDP sockets under test
receive the host's packets among their own. The tests count and inspect
what they receive, so a preconfigured host fails some of them in every
mode, and a bare one passes.

Run the veth part in an unnamed network namespace with its own sysfs,
which drops with its last process whenever the run ends. only -d names
it, its pair outlives the run. The fragment limit came from the sysctl
max_skb_frags, which has no file outside the initial namespace. Take it
from the kernel's BTF as the size of skb_shared_info's frags array, fall
back to sysctl as before if this info is missing. When the namespace
can't be created, the tests are skipped, as without veth or ip. Other
cases after a successful namespace creation fail.

Fix test_exit() return status for skips, as since commit 895b62eed2ab
("selftests: xsk: fix reporting of failed tests"), test_exit() exited 1.

https://virtuozzo.atlassian.net/browse/VSTOR-150731
Feature: fix selftests

Signed-off-by: Eva Kurchatova <eva.kurchatova@virtuozzo.com>
---
 tools/testing/selftests/bpf/test_xsk.sh    | 30 +++++++++++++++--
 tools/testing/selftests/bpf/xsk_prereqs.sh |  2 +-
 tools/testing/selftests/bpf/xskxceiver.c   | 39 +++++++++++++++++++++-
 3 files changed, 67 insertions(+), 4 deletions(-)

diff --git a/tools/testing/selftests/bpf/test_xsk.sh b/tools/testing/selftests/bpf/test_xsk.sh
index 65aafe0003db..218528ddcdf8 100755
--- a/tools/testing/selftests/bpf/test_xsk.sh
+++ b/tools/testing/selftests/bpf/test_xsk.sh
@@ -68,7 +68,8 @@
 # Run with verbose output:
 #   sudo ./test_xsk.sh -v
 #
-# Set up veth interfaces and leave them up so xskxceiver can be launched in a debugger:
+# Set up veth interfaces in a network namespace and leave them up so
+# xskxceiver can be launched in a debugger there:
 #   sudo ./test_xsk.sh -d
 #
 # Run test suite for physical device in loopback mode
@@ -162,8 +163,33 @@ if [ ! -z $ETH ]; then
 	VETH1=${ETH}
 else
 	validate_root_exec
-	validate_veth_support ${VETH0}
 	validate_ip_utility
+	# The host configures and talks on any new interface in its namespace
+	if [ -z "$XSK_NETNS" ]; then
+		if ! unshare --net true; then
+			echo "skip all tests: cannot create a network namespace" >&2
+			test_exit $ksft_skip
+		fi
+		if [[ $debug -ne 1 ]]; then
+			# Unnamed, it goes with its last process; its own sysfs shows its interfaces
+			XSK_NETNS=1 exec unshare --net --mount sh -c \
+				'mount --make-rprivate / && mount -t sysfs sysfs /sys &&
+				exec bash "$0" "$@"' "$0" "$@"
+		fi
+		# The pair of a run by hand outlives it, in a namespace with a name
+		XSK_NETNS=xsk${VETH0_POSTFIX}
+		ip netns add ${XSK_NETNS} || exit 1
+		trap "ip netns del ${XSK_NETNS}" EXIT
+		# This run's veth names were never created; the pair is in the namespace
+		trap "exit 1" INT
+		XSK_NETNS=${XSK_NETNS} ip netns exec ${XSK_NETNS} bash "$0" "$@" || exit
+		trap - EXIT
+		echo "The pair is up in network namespace ${XSK_NETNS}," \
+			"use ip netns exec ${XSK_NETNS};" \
+			"ip netns del ${XSK_NETNS} removes it"
+		exit 0
+	fi
+	validate_veth_support ${VETH0}
 	setup_vethPairs
 
 	retval=$?
diff --git a/tools/testing/selftests/bpf/xsk_prereqs.sh b/tools/testing/selftests/bpf/xsk_prereqs.sh
index 47c7b8064f38..12176d85cd6c 100755
--- a/tools/testing/selftests/bpf/xsk_prereqs.sh
+++ b/tools/testing/selftests/bpf/xsk_prereqs.sh
@@ -50,7 +50,7 @@ test_exit()
 	if [ $1 -ne 0 ]; then
 		test_status $1 $(basename $0)
 	fi
-	exit 1
+	exit $1
 }
 
 cleanup_iface()
diff --git a/tools/testing/selftests/bpf/xskxceiver.c b/tools/testing/selftests/bpf/xskxceiver.c
index 11f047b8af75..a4a0b4e2516c 100644
--- a/tools/testing/selftests/bpf/xskxceiver.c
+++ b/tools/testing/selftests/bpf/xskxceiver.c
@@ -103,6 +103,7 @@
 #include "xsk.h"
 #include "xskxceiver.h"
 #include <bpf/bpf.h>
+#include <bpf/btf.h>
 #include <linux/filter.h>
 #include "../kselftest.h"
 #include "xsk_xdp_common.h"
@@ -325,12 +326,48 @@ static bool ifobj_zc_avail(struct ifobject *ifobject)
 	return zc_avail;
 }
 
+/* AF_XDP checks MAX_SKB_FRAGS, which the sysctl only follows by default */
+static unsigned int btf_max_skb_frags(void)
+{
+	unsigned int max_skb_frags = 0;
+	const struct btf_member *m;
+	const struct btf_type *t;
+	struct btf *btf;
+	int id, i;
+
+	btf = btf__load_vmlinux_btf();
+	if (!btf)
+		return 0;
+
+	id = btf__find_by_name_kind(btf, "skb_shared_info", BTF_KIND_STRUCT);
+	if (id < 0)
+		goto out;
+
+	t = btf__type_by_id(btf, id);
+	m = btf_members(t);
+	for (i = 0; i < btf_vlen(t); i++, m++) {
+		if (strcmp(btf__name_by_offset(btf, m->name_off), "frags"))
+			continue;
+		t = btf__type_by_id(btf, m->type);
+		if (btf_is_array(t))
+			max_skb_frags = btf_array(t)->nelems;
+		break;
+	}
+out:
+	btf__free(btf);
+	return max_skb_frags;
+}
+
 #define MAX_SKB_FRAGS_PATH "/proc/sys/net/core/max_skb_frags"
 static unsigned int get_max_skb_frags(void)
 {
-	unsigned int max_skb_frags = 0;
+	unsigned int max_skb_frags = btf_max_skb_frags();
 	FILE *file;
 
+	if (max_skb_frags)
+		return max_skb_frags;
+
+	ksft_print_msg("No MAX_SKB_FRAGS in the kernel's BTF, reading %s\n", MAX_SKB_FRAGS_PATH);
 	file = fopen(MAX_SKB_FRAGS_PATH, "r");
 	if (!file) {
 		ksft_print_msg("Error opening %s\n", MAX_SKB_FRAGS_PATH);
-- 
2.56.0

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