[Devel] [PATCH hci-8.1 v3 0/1] selftests/bpf: run the xsk veth tests in a network namespace of their own

[Devel] [PATCH hci-8.1 v3 0/1] selftests/bpf: run the xsk veth tests in a network namespace of their own

[Eva Kurchatova]

Patch for task https://virtuozzo.atlassian.net/browse/VSTOR-150731

Changes in v3:

- The namespace is unnamed, so it goes with its last process however
  the run ends, Ctrl-C, a timeout or a kill, and no outer run is left
  to delete host interfaces. Passing -d uses a pre-existing interface.
- Obtain max_skb_frags from the kernel BTF, removing -f option.
- Fix test_exit() exit status for skipped runs.
- With -d, the namespace is kept.
- Rebased.

Link to v2: http://lore.virtuozzo.com/kernel/20261022024816.2435565-1-eva.kurchatova@virtuozzo.com/T/#t

Changes in v2:

- -f is checked as the sysctl is, 1 to 45 and digits only, so a value
  that would wrap the fragment count or the packet array is refused.
- -f goes into the namespace only when the host's sysctl file could be
  read; a bare -f made getopts complain.
- No network namespace skips the tests, as no veth support does, rather
  than failing them.
- The -f description says the option tells the tests the kernel's limit
  and changes nothing in the kernel.
- The -d hint names the namespace in a usable form.
- test_exit() exits 1 for a skip as it does for the veth one; as the
  script has it.

Link to v1: http://lore.virtuozzo.com/kernel/20261020041218.1659392-1-eva.kurchatova@virtuozzo.com/T/#t

Eva Kurchatova (1):
  selftests/bpf: run the xsk veth tests in a network namespace of their
    own

 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(-)

-- 
2.56.0

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

[Eva Kurchatova]

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

[no-reply]

Thank you for your contribution! Sashiko AI review found 3 potential issue(s) to consider:
- [Low] selftests/bpf: unrelated test_exit() fix and internal tracker tags bundled in
- [Low] selftests/bpf: test_xsk.sh skip probe misses the --mount and sysfs steps it later needs
- [Low] selftests/bpf: xskxceiver sysctl fallback for max_skb_frags is dead in the new netns
--

commit e15fddae4e72be15308b41d2c75c44585ec9c80f
Author: Eva Kurchatova <eva.kurchatova@virtuozzo.com>

selftests/bpf: run the xsk veth tests in a network namespace of their own

This patch makes test_xsk.sh run the veth part of the xsk tests inside a
private network namespace. It also reads the fragment limit from the
kernel's BTF, with the sysctl as a fallback. It also changes test_exit() to
exit with its argument instead of always exiting 1.

> selftests/bpf: run the xsk veth tests in a network namespace of their own

[Severity: Low]
This isn't a bug, but the commit message contains an internal tracker URL
and a trailer that mean nothing upstream:

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

Could these two lines be dropped?

The test_exit() change below is also a standalone fix, described in the
commit message as "Fix test_exit() return status for skips, as since commit
895b62eed2ab ("selftests: xsk: fix reporting of failed tests"), test_exit()
exited 1."

Would it be better as a separate patch with a Fixes: tag, so it can be
backported and bisected on its own?

> diff --git a/tools/testing/selftests/bpf/test_xsk.sh b/tools/testing/selftests/bpf/test_xsk.sh
> --- a/tools/testing/selftests/bpf/test_xsk.sh
> +++ b/tools/testing/selftests/bpf/test_xsk.sh

[ ... ]

> @@ -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

[Severity: Low]
Can this turn a skip into a failure? The probe only runs unshare --net
true. The --mount, mount --make-rprivate / and mount -t sysfs sysfs /sys
steps are not probed.

If the namespace probe succeeds but one of those mount steps is denied (for
example by an LSM, a seccomp filter, or a user namespace setup where sysfs
cannot be mounted), the sh -c command exits non-zero.

The exec has already replaced the script by then, so test_exit $ksft_skip
can no longer run. The caller sees a failure instead of a skip.

The commit message says "Other cases after a successful namespace creation
fail."

Should the probe cover the mount steps as well, for example by running the
same unshare --net --mount sh -c 'mount ...' sequence with true in place of
the final exec bash?

[ ... ]

> diff --git a/tools/testing/selftests/bpf/xskxceiver.c b/tools/testing/selftests/bpf/xskxceiver.c
> --- a/tools/testing/selftests/bpf/xskxceiver.c
> +++ b/tools/testing/selftests/bpf/xskxceiver.c

[ ... ]

>  #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);

[Severity: Low]
Is the sysctl fallback reachable for the veth runs? test_xsk.sh now always
re-execs into a private network namespace for the veth tests.

In net/core/sysctl_net_core.c, max_skb_frags is in net_core_table, which is
registered only for init_net:

    register_net_sysctl(&init_net, "net/core", net_core_table);

Non-init namespaces get only netns_core_table. So inside the new namespace
the fopen() above always fails, get_max_skb_frags() returns 0, and the
caller falls back to its hardcoded value:

    max_frags = get_max_skb_frags();
    if (!max_frags) {
        ksft_print_msg("Couldn't retrieve MAX_SKB_FRAGS from system, using default (17) value\n");
        max_frags = 17;
    }

On a kernel without vmlinux BTF and with CONFIG_MAX_SKB_FRAGS other than 17,
can the veth multi-buffer tests then fail spuriously?

The fallback still works for -i physical-device runs and for xskxceiver run
by hand in the init namespace. The commit message says "fall back to sysctl
as before if this info is missing", which does not hold for the veth flow.

> diff --git a/tools/testing/selftests/bpf/xsk_prereqs.sh b/tools/testing/selftests/bpf/xsk_prereqs.sh
> --- 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
>  }

This is the test_exit() change mentioned above.

-- 
Sashiko AI review · https://sashiko.vzint.dev/#/patchset/20261026012309.458048-1-eva.kurchatova@virtuozzo.com?part=1

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

[Eva Kurchatova (Virtuozzo)]

On 10/26/26 03:29, no-reply@sashiko.virtuozzo.com wrote:
> Thank you for your contribution! Sashiko AI review found 3 potential issue(s) to consider:
> - [Low] selftests/bpf: unrelated test_exit() fix and internal tracker tags bundled in
> - [Low] selftests/bpf: test_xsk.sh skip probe misses the --mount and sysfs steps it later needs
> - [Low] selftests/bpf: xskxceiver sysctl fallback for max_skb_frags is dead in the new netns
> --
>
> commit e15fddae4e72be15308b41d2c75c44585ec9c80f
> Author: Eva Kurchatova <eva.kurchatova@virtuozzo.com>
>
> selftests/bpf: run the xsk veth tests in a network namespace of their own
>
> This patch makes test_xsk.sh run the veth part of the xsk tests inside a
> private network namespace. It also reads the fragment limit from the
> kernel's BTF, with the sysctl as a fallback. It also changes test_exit() to
> exit with its argument instead of always exiting 1.
>
>> selftests/bpf: run the xsk veth tests in a network namespace of their own
> [Severity: Low]
> This isn't a bug, but the commit message contains an internal tracker URL
> and a trailer that mean nothing upstream:
>
>> https://virtuozzo.atlassian.net/browse/VSTOR-150731
>> Feature: fix selftests
> Could these two lines be dropped?

Um, this is a vzkernel patch

> The test_exit() change below is also a standalone fix, described in the
> commit message as "Fix test_exit() return status for skips, as since commit
> 895b62eed2ab ("selftests: xsk: fix reporting of failed tests"), test_exit()
> exited 1."
>
> Would it be better as a separate patch with a Fixes: tag, so it can be
> backported and bisected on its own?
I have decided that such a small change should be bundled here, if the 
v2 is not accepted to begin with. This patch will be sent in similar 
form, albeit altered due to upstream having many changes in this kselftest.
>> diff --git a/tools/testing/selftests/bpf/test_xsk.sh b/tools/testing/selftests/bpf/test_xsk.sh
>> --- a/tools/testing/selftests/bpf/test_xsk.sh
>> +++ b/tools/testing/selftests/bpf/test_xsk.sh
> [ ... ]
>
>> @@ -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
> [Severity: Low]
> Can this turn a skip into a failure? The probe only runs unshare --net
> true. The --mount, mount --make-rprivate / and mount -t sysfs sysfs /sys
> steps are not probed.
>
> If the namespace probe succeeds but one of those mount steps is denied (for
> example by an LSM, a seccomp filter, or a user namespace setup where sysfs
> cannot be mounted), the sh -c command exits non-zero.
>
> The exec has already replaced the script by then, so test_exit $ksft_skip
> can no longer run. The caller sees a failure instead of a skip.
>
> The commit message says "Other cases after a successful namespace creation
> fail."
>
> Should the probe cover the mount steps as well, for example by running the
> same unshare --net --mount sh -c 'mount ...' sequence with true in place of
> the final exec bash?
The failure here is intentional, it is either a test bug or a very 
misconfigured host.
> [ ... ]
>
>> diff --git a/tools/testing/selftests/bpf/xskxceiver.c b/tools/testing/selftests/bpf/xskxceiver.c
>> --- a/tools/testing/selftests/bpf/xskxceiver.c
>> +++ b/tools/testing/selftests/bpf/xskxceiver.c
> [ ... ]
>
>>   #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);
> [Severity: Low]
> Is the sysctl fallback reachable for the veth runs? test_xsk.sh now always
> re-execs into a private network namespace for the veth tests.
>
> In net/core/sysctl_net_core.c, max_skb_frags is in net_core_table, which is
> registered only for init_net:
>
>      register_net_sysctl(&init_net, "net/core", net_core_table);
>
> Non-init namespaces get only netns_core_table. So inside the new namespace
> the fopen() above always fails, get_max_skb_frags() returns 0, and the
> caller falls back to its hardcoded value:
>
>      max_frags = get_max_skb_frags();
>      if (!max_frags) {
>          ksft_print_msg("Couldn't retrieve MAX_SKB_FRAGS from system, using default (17) value\n");
>          max_frags = 17;
>      }
>
> On a kernel without vmlinux BTF and with CONFIG_MAX_SKB_FRAGS other than 17,
> can the veth multi-buffer tests then fail spuriously?

VZkernel only builds with BTF in production. The test never could run in 
a separate namespace before this patch; This is the whole point. It also 
follows the established practice in bpf selftests.

> The fallback still works for -i physical-device runs and for xskxceiver run
> by hand in the init namespace. The commit message says "fall back to sysctl
> as before if this info is missing", which does not hold for the veth flow.
>
>> diff --git a/tools/testing/selftests/bpf/xsk_prereqs.sh b/tools/testing/selftests/bpf/xsk_prereqs.sh
>> --- 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
>>   }
> This is the test_exit() change mentioned above.
>
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Re: [Devel] [PATCH hci-8.1 v3 1/1] selftests/bpf: run the xsk veth tests in a network namespace of their own

[Konstantin Khorenko]

Hi Eva,

thanks, all comments on v2 are addressed, and the code does what the
message says. What is left is the commit message, the split and one
redundant mount. To save a round, I reworked it myself and am posting
it as v4, three patches:

  1/3 selftests/bpf: xsk: exit with the status test_exit() is given
  2/3 selftests/bpf: xsk: take the fragment limit from the kernel's BTF
  3/3 selftests/bpf: run the xsk veth tests in a network namespace of
      their own

Please check that v4 still says what you meant. Details below.

> 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.

For the veth runs the sysctl fallback cannot work any more:
max_skb_frags is in net_core_table, which is registered for init_net
only, and the veth part now always runs in a namespace of its own.
Sashiko was right about the message here. On our kernels it changes
nothing, BTF is always built in, but "as before" is not true. The
sysctl stays a fallback for kernels without BTF, which in practice
means -i runs in the initial namespace.

"only -d names it, its pair outlives the run" also needs a capital
letter and a "so".

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

This is a fix of its own, with its own Fixes: tag, and mainline needs
the same one-liner: it still has "exit 1" there. As a separate commit
it can later be replaced by its ms/ version; folded into this patch it
cannot.

The BTF part is a fix of its own too: AF_XDP checks MAX_SKB_FRAGS
(xsk_build_skb()), not the sysctl, so a lowered sysctl makes
too_many_frags expect the wrong limit in any namespace.

>
> 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 "$0" "$@"' "$0" "$@"

unshare --mount already sets private propagation on the new mount
namespace by default (--propagation private), so the
"mount --make-rprivate /" step does nothing.

> +             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);
>
[ ... ]

Mainline
--------

VSTOR-151679 needs a few updates:

- "without the -f option vz adds" is stale: v4 has no -f.
- Order: the test_exit() fix first, it stands alone and carries a
  Fixes: tag; then BTF; then the namespace.
- Mainline reads the sysctl in two places, xskxceiver.c and
  prog_tests/xsk.c (both via read_procfs_val(MAX_SKB_FRAGS_PATH), both
  fall back to 17). Put the BTF helper into prog_tests/test_xsk.c,
  which both use, and replace both reads.
- prog_tests/xdp_adjust_frags.c reads the same sysctl. It is a
  different test, but expect the question in review.
- In mainline the veth runs already exist in test_progs, in a namespace
  of their own (test_ns_xsk_skb, test_ns_xsk_drv). The reviewers may
  prefer dropping the veth mode from test_xsk.sh to isolating it. Look
  at what test_xsk.sh still covers that test_progs does not, busy poll
  for instance, and say it in the cover letter.

--
Best regards,

Konstantin Khorenko,
Virtuozzo Linux Kernel Team

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