Dpdk: add a uevent listener helper app by mcgov · Pull Request #4661 · microsoft/lisa

mcgov (mcgov) · 2026-08-12T12:50:55Z

Part 8 of 9 of a stacked series that reworks the DPDK SRIOV hot plug tests. Stacked on #4660, review only the last commit. This adds a single new C source file and changes no Python.

Hot plug tests need to know exactly when the kernel adds or removes a VF, its uverbs node, its ib device and its netdev. DPDK's own rte_dev_event_monitor only parses pci, uio and vfio events that carry PCI_SLOT_NAME, so it drops every vmbus, net and infiniband uevent that matters on Azure.

This helper listens on NETLINK_KOBJECT_UEVENT directly and prints a tagged, single line per event that the tests can match on. It is consumed by the next PR in the stack.

Key Test Cases:
verify_dpdk_sriov_rescind_failover_send_only

Impacted LISA Features:
Sriov, NetworkInterface

Tested Azure Marketplace Images:

canonical 0001-com-ubuntu-server-jammy 22_04-lts latest

Copilot

Pull request overview

This PR adds a small standalone C helper (azure_uevent_listener.c) under the DPDK test suite that listens directly to NETLINK_KOBJECT_UEVENT and prints one tagged line per kernel uevent relevant to Azure NIC hotplug (net, vmbus, infiniband, pci), enabling higher-level DPDK SR-IOV hotplug tests to reliably match the precise device-add/remove sequence.

Changes:

Add a netlink uevent listener that classifies and prints Azure NIC-related uevents with stable, parseable tags.
Include optional modes to print all subsystems (-a) and dump raw key/value properties (-v).

Suppressed comments (1)

lisa/microsoft/testsuites/dpdk/uevent_listener/azure_uevent_listener.c:367

The -h option is implemented but not documented in usage(), and the usage line doesn’t mention it. This makes CLI help incomplete.

	fprintf(stderr,
		"usage: %s [-a] [-v]\n"
		"  -a  report every subsystem, not just Azure NIC events\n"
		"  -v  dump all uevent properties for each reported event\n",
		argv0);

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+static void
+print_event(const struct uevent *ev, const char *tag, bool vf)
+{
+	struct timespec ts;


+ * Build:
+ *   gcc -O2 -Wall -Wextra -o azure-hotplug-mon azure_hotplug_mon.c
+ *


+	cm = CMSG_FIRSTHDR(&msg);
+	if (cm == NULL || cm->cmsg_type != SCM_CREDENTIALS)
+		return 0;
+	cred = (struct ucred *)CMSG_DATA(cm);
+	if (cred->uid != 0)
+		return 0;


Copilot

Pull request overview

Copilot reviewed 1 out of 1 changed files in this pull request and generated no new comments.

Suppressed comments (3)

lisa/microsoft/testsuites/dpdk/uevent_listener/azure_uevent_listener.c:177

struct timespec ts is used in the timestamp (ts.tv_nsec) even if clock_gettime() fails, leaving ts uninitialized and causing undefined behavior in the printed output. Initialize ts so the fallback path is safe.

	struct timespec ts;

lisa/microsoft/testsuites/dpdk/uevent_listener/azure_uevent_listener.c:21

The build command in the header comment references a non-existent source file (azure_hotplug_mon.c). Copy/pasting this command will fail because the actual file name is azure_uevent_listener.c.

 * Build:
 *   gcc -O2 -Wall -Wextra -o azure-hotplug-mon azure_hotplug_mon.c

lisa/microsoft/testsuites/dpdk/uevent_listener/azure_uevent_listener.c:158

classify() returns PCI_ADD/PCI_REMOVE for non-Azure-VF PCI events. That means the program will print unrelated PCI hotplug events even when -a is not specified, contradicting the comment that non-Azure NIC cases are dropped unless -a is given.

	if (strcmp(ev->subsystem, "pci") == 0) {
		if (vf)
			return add ? "VF_PCI_ADD" : "VF_PCI_REMOVE";
		return add ? "PCI_ADD" : "PCI_REMOVE";
	}

Copilot

Pull request overview

Copilot reviewed 1 out of 1 changed files in this pull request and generated no new comments.

Suppressed comments (3)

lisa/microsoft/testsuites/dpdk/uevent_listener/azure_uevent_listener.c:177

ts may be uninitialized if clock_gettime() fails, but it is still used in the timestamp print (ts.tv_nsec). Initializing it avoids undefined behavior and keeps output deterministic on failure paths.

	struct timespec ts;

lisa/microsoft/testsuites/dpdk/uevent_listener/azure_uevent_listener.c:295

recvmsg() ancillary data can include multiple control messages; relying on CMSG_FIRSTHDR() being SCM_CREDENTIALS may cause all events to be skipped on kernels that prepend other cmsgs (e.g. pktinfo). Iterate cmsgs to find SCM_CREDENTIALS and validate it.

	if (cm == NULL || cm->cmsg_type != SCM_CREDENTIALS)
		return 0;
	cred = (struct ucred *)CMSG_DATA(cm);
	if (cred->uid != 0)
		return 0;

lisa/microsoft/testsuites/dpdk/uevent_listener/azure_uevent_listener.c:22

The build command in the header comment refers to azure_hotplug_mon.c, but this file is azure_uevent_listener.c. Updating it prevents copy/paste build failures for anyone following the inline instructions.

 * Build:
 *   gcc -O2 -Wall -Wextra -o azure-hotplug-mon azure_hotplug_mon.c
 *

Copilot

Pull request overview

Copilot reviewed 1 out of 1 changed files in this pull request and generated no new comments.

Suppressed comments (2)

lisa/microsoft/testsuites/dpdk/uevent_listener/azure_uevent_listener.c:22

The build instruction references azure_hotplug_mon.c, but this PR adds azure_uevent_listener.c. As written, the example command won’t compile on a fresh checkout. Update the command to use the actual source filename (or rename the file to match the documentation).

 * Build:
 *   gcc -O2 -Wall -Wextra -o azure-hotplug-mon azure_hotplug_mon.c
 *

lisa/microsoft/testsuites/dpdk/uevent_listener/azure_uevent_listener.c:177

ts is used in the printf even if clock_gettime() fails, but it’s currently uninitialized. Initialize it to avoid undefined behavior in that error path.

	struct timespec ts;

Copilot

Pull request overview

Copilot reviewed 1 out of 1 changed files in this pull request and generated no new comments.

Suppressed comments (2)

lisa/microsoft/testsuites/dpdk/uevent_listener/azure_uevent_listener.c:22

The build instructions reference azure_hotplug_mon.c, but this file doesn’t exist in the repo (this PR adds azure_uevent_listener.c). As written, the example build command will fail. Update the command to compile the actual source file name (or rename the file to match the documented command).

 * Build:
 *   gcc -O2 -Wall -Wextra -o azure-hotplug-mon azure_hotplug_mon.c
 *

lisa/microsoft/testsuites/dpdk/uevent_listener/azure_uevent_listener.c:181

ts.tv_nsec is used in the printf even if clock_gettime() fails, leaving ts uninitialized (undefined behavior and can trigger compiler warnings). Initialize ts and only print milliseconds when the timestamp was captured successfully (or default to 0).

	struct timespec ts;
	struct tm tm;
	char when[16] = "??:??:??";

	if (clock_gettime(CLOCK_REALTIME, &ts) == 0 &&

Copilot

Pull request overview

Copilot reviewed 1 out of 1 changed files in this pull request and generated no new comments.

Suppressed comments (3)

lisa/microsoft/testsuites/dpdk/uevent_listener/azure_uevent_listener.c:22

The build command in the header comment references azure_hotplug_mon.c, but this file is named azure_uevent_listener.c. As written, the copy/paste build instructions will fail.

 * Build:
 *   gcc -O2 -Wall -Wextra -o azure-hotplug-mon azure_hotplug_mon.c
 *

lisa/microsoft/testsuites/dpdk/uevent_listener/azure_uevent_listener.c:177

ts is used in the printf even if clock_gettime() fails, leaving ts.tv_nsec uninitialized (undefined behavior). Initialize ts (or guard the sub-second print) so failure still prints deterministically.

	struct timespec ts;

lisa/microsoft/testsuites/dpdk/uevent_listener/azure_uevent_listener.c:294

uev_recv() assumes the first control message is SCM_CREDENTIALS. If the kernel ever sends additional cmsgs (or ordering differs), this will incorrectly drop otherwise-valid uevents. Iterate the control messages and also verify cmsg_level == SOL_SOCKET.

	cm = CMSG_FIRSTHDR(&msg);
	if (cm == NULL || cm->cmsg_type != SCM_CREDENTIALS)
		return 0;
	cred = (struct ucred *)CMSG_DATA(cm);
	if (cred->uid != 0)

Copilot

Pull request overview

Copilot reviewed 1 out of 1 changed files in this pull request and generated no new comments.

Suppressed comments (4)

lisa/microsoft/testsuites/dpdk/uevent_listener/azure_uevent_listener.c:294

uev_recv() drops the message unless SCM_CREDENTIALS is present as the first control message. This makes the listener silently stop working if SO_PASSCRED can't be enabled, and it may also reject valid kernel messages if credentials aren't the first cmsg. Consider accepting messages from nl_pid==0, and only enforcing uid==0 when credentials are present (iterating over all cmsgs and checking cmsg_level/type).

	cm = CMSG_FIRSTHDR(&msg);
	if (cm == NULL || cm->cmsg_type != SCM_CREDENTIALS)
		return 0;
	cred = (struct ucred *)CMSG_DATA(cm);
	if (cred->uid != 0)

lisa/microsoft/testsuites/dpdk/uevent_listener/azure_uevent_listener.c:22

The build command in the file header references a different source filename (azure_hotplug_mon.c) than this file (azure_uevent_listener.c), which will confuse anyone trying to compile it from the instructions.

 * Build:
 *   gcc -O2 -Wall -Wextra -o azure-hotplug-mon azure_hotplug_mon.c
 *

lisa/microsoft/testsuites/dpdk/uevent_listener/azure_uevent_listener.c:185

If clock_gettime() fails, ts is uninitialized but ts.tv_nsec is still used in the printf(), which can print garbage or trigger undefined behavior. Initialize ts and/or compute the millisecond field only on success.

	if (clock_gettime(CLOCK_REALTIME, &ts) == 0 &&
	    localtime_r(&ts.tv_sec, &tm) != NULL)
		strftime(when, sizeof(when), "%H:%M:%S", &tm);

	printf("[%s.%03ld] %-18s subsystem=%s", when, ts.tv_nsec / 1000000,

lisa/microsoft/testsuites/dpdk/uevent_listener/azure_uevent_listener.c:367

-h is supported (getopt string includes 'h'), but usage() doesn't document it. This makes the CLI help output incomplete.

	fprintf(stderr,
		"usage: %s [-a] [-v]\n"
		"  -a  report every subsystem, not just Azure NIC events\n"
		"  -v  dump all uevent properties for each reported event\n",
		argv0);

Copilot

Pull request overview

Copilot reviewed 1 out of 1 changed files in this pull request and generated no new comments.

Suppressed comments (2)

lisa/microsoft/testsuites/dpdk/uevent_listener/azure_uevent_listener.c:186

ts is used in the timestamp printf even when clock_gettime() fails, leaving ts.tv_nsec uninitialized and causing undefined output. Initialize ts (or only print subseconds when the call succeeds).

	struct timespec ts;
	struct tm tm;
	char when[16] = "??:??:??";

	if (clock_gettime(CLOCK_REALTIME, &ts) == 0 &&
	    localtime_r(&ts.tv_sec, &tm) != NULL)
		strftime(when, sizeof(when), "%H:%M:%S", &tm);

	printf("[%s.%03ld] %-18s subsystem=%s", when, ts.tv_nsec / 1000000,
	       tag, ev->subsystem != NULL ? ev->subsystem : "?");

lisa/microsoft/testsuites/dpdk/uevent_listener/azure_uevent_listener.c:22

The build command in the header comment references azure_hotplug_mon.c, but this PR adds azure_uevent_listener.c. As written, the copy/paste build instruction will fail.

 * Build:
 *   gcc -O2 -Wall -Wextra -o azure-hotplug-mon azure_hotplug_mon.c
 *

Copilot

Pull request overview

Copilot reviewed 1 out of 1 changed files in this pull request and generated no new comments.

Suppressed comments (3)

lisa/microsoft/testsuites/dpdk/uevent_listener/azure_uevent_listener.c:22

Build instructions reference azure_hotplug_mon.c, but this file is named azure_uevent_listener.c. As written, the documented compile command will fail unless the file is renamed.

 * Build:
 *   gcc -O2 -Wall -Wextra -o azure-hotplug-mon azure_hotplug_mon.c
 *

lisa/microsoft/testsuites/dpdk/uevent_listener/azure_uevent_listener.c:181

print_event() uses ts.tv_nsec in the printf even if clock_gettime() fails, which leaves ts uninitialized and can print garbage milliseconds. Initialize ts (or gate the millisecond printing on a successful clock_gettime).

	struct timespec ts;
	struct tm tm;
	char when[16] = "??:??:??";

	if (clock_gettime(CLOCK_REALTIME, &ts) == 0 &&

lisa/microsoft/testsuites/dpdk/uevent_listener/azure_uevent_listener.c:368

-h is accepted by getopt and handled, but it is not documented in usage(). This makes the CLI help inconsistent with the actual flags.

	fprintf(stderr,
		"usage: %s [-a] [-v]\n"
		"  -a  report every subsystem, not just Azure NIC events\n"
		"  -v  dump all uevent properties for each reported event\n",
		argv0);

Copilot

Pull request overview

Copilot reviewed 1 out of 1 changed files in this pull request and generated no new comments.

Suppressed comments (3)

lisa/microsoft/testsuites/dpdk/uevent_listener/azure_uevent_listener.c:22

The build command references azure_hotplug_mon.c, but this file is named azure_uevent_listener.c in the repo, so the command as written will fail when copy/pasted. Update the filename in the build instructions.

 * Build:
 *   gcc -O2 -Wall -Wextra -o azure-hotplug-mon azure_hotplug_mon.c
 *

lisa/microsoft/testsuites/dpdk/uevent_listener/azure_uevent_listener.c:177

ts is used in the printf format even when clock_gettime() fails, which leaves ts.tv_nsec uninitialized and can print garbage timestamps. Initialize ts to a known value before the call.

	struct timespec ts;

lisa/microsoft/testsuites/dpdk/uevent_listener/azure_uevent_listener.c:367

-h is supported (and getopt accepts it), but the usage text doesn’t mention it. This makes the CLI help incomplete.

	fprintf(stderr,
		"usage: %s [-a] [-v]\n"
		"  -a  report every subsystem, not just Azure NIC events\n"
		"  -v  dump all uevent properties for each reported event\n",
		argv0);

Hot plug tests need to know exactly when the kernel adds or removes a VF, its uverbs node, its ib device and its netdev, but DPDK's own rte_dev_event_monitor only parses pci, uio and vfio events that carry PCI_SLOT_NAME, so it drops every vmbus, net and infiniband uevent that matters on Azure. Add a small helper that listens on NETLINK_KOBJECT_UEVENT directly and prints a tagged, single line per event that tests can match on. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> Copilot-Session: 5d5f58ad-b9df-4420-ad37-22caee78e925

Copilot

Pull request overview

Copilot reviewed 1 out of 1 changed files in this pull request and generated no new comments.

Suppressed comments (4)

lisa/microsoft/testsuites/dpdk/uevent_listener/azure_uevent_listener.c:186

Major: print_event() uses ts.tv_nsec in the log line even if clock_gettime() fails, leaving ts uninitialized and resulting in undefined behavior / garbage timestamps.

	struct timespec ts;
	struct tm tm;
	char when[16] = "??:??:??";

	if (clock_gettime(CLOCK_REALTIME, &ts) == 0 &&
	    localtime_r(&ts.tv_sec, &tm) != NULL)
		strftime(when, sizeof(when), "%H:%M:%S", &tm);

	printf("[%s.%03ld] %-18s subsystem=%s", when, ts.tv_nsec / 1000000,
	       tag, ev->subsystem != NULL ? ev->subsystem : "?");

lisa/microsoft/testsuites/dpdk/uevent_listener/azure_uevent_listener.c:295

Major: if SO_PASSCRED can't be enabled (you already warn and continue), uev_recv() will drop all messages because it requires SCM_CREDENTIALS. Also, the cmsg check should validate cmsg_level == SOL_SOCKET. Consider treating credentials as an optional extra filter: only enforce uid==0 when credentials are present.

	/* Only the kernel (port id 0, uid 0) is allowed to talk to us. */
	if (snl.nl_pid != 0)
		return 0;

	cm = CMSG_FIRSTHDR(&msg);
	if (cm == NULL || cm->cmsg_type != SCM_CREDENTIALS)
		return 0;
	cred = (struct ucred *)CMSG_DATA(cm);
	if (cred->uid != 0)
		return 0;

lisa/microsoft/testsuites/dpdk/uevent_listener/azure_uevent_listener.c:22

Minor: the build instructions reference azure_hotplug_mon.c, but this file is named azure_uevent_listener.c. This can confuse users trying to build the helper.

 * Build:
 *   gcc -O2 -Wall -Wextra -o azure-hotplug-mon azure_hotplug_mon.c
 *

lisa/microsoft/testsuites/dpdk/uevent_listener/azure_uevent_listener.c:367

Nit: -h is accepted by getopt, but it isn't shown in the usage text.

	fprintf(stderr,
		"usage: %s [-a] [-v]\n"
		"  -a  report every subsystem, not just Azure NIC events\n"
		"  -v  dump all uevent properties for each reported event\n",
		argv0);

mcgov (mcgov) requested review from LiliDeng and Johnson (johnsongeorge-w) as code owners August 12, 2026 12:50

mcgov (mcgov) mentioned this pull request Aug 12, 2026

Dpdk: hotplug reliability, ready platform support, and nic selection fixes #4662

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Dpdk: add a uevent listener helper app - #4661

Dpdk: add a uevent listener helper app#4661
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mcgov (mcgov) commented Aug 12, 2026

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