Handle.FilterList() produces 0 results

[lorenzocipriani]

It looks like the FilterList() function doesn't return the expected results.

Given this snippet of sample code:

netlinkHandle, err := netlink.NewHandle()
if err != nil {
	fmt.Printf("HANDLE ERROR: %v", err)
}

fmt.Printf("\n\n[tc qdisc show]\n")
qdiscs, err := netlinkHandle.QdiscList(nil)
if err != nil {
	logger.Error().
		Err(err).
		Msg("cannot get the qdiscs list")
}

for _, qdisc := range qdiscs {

	if qdisc.Type() == "clsact" && qdisc.Attrs().Parent == netlink.HANDLE_INGRESS {
		fmt.Printf("\nQDISC:[%s]\n%s\n", qdisc.Type(), qdisc.Attrs().String())

		if link, err := netlinkHandle.LinkByIndex(qdisc.Attrs().LinkIndex); err == nil {
			fmt.Printf("[tc filter show %s dev %s]\n", netlink.HandleStr(qdisc.Attrs().Parent), link.Attrs().Name)
			fmt.Printf("LINK:\n%+v\n", link)

			filters, _ := netlinkHandle.FilterList(link, qdisc.Attrs().Parent)
			fmt.Printf("FILTERS: %d\n", len(filters))
			
			for _, filter := range filters {
				fmt.Printf("FILTER:[%s]\n%+v\n", filter.Type(), filter.Attrs())
			}
		}
	}
}

I expected to see a couple of entries for each link, but the result shows 0 filters defined for the given links:

[tc qdisc show]

QDISC:[clsact]
{LinkIndex: 3, Handle: ffff:0, Parent: ingress, Refcnt: 1}
[tc filter show ingress dev eno1]
LINK:
&{LinkAttrs:{Index:3 ... Name:eno1 ... }}
FILTERS: 0

QDISC:[clsact]
{LinkIndex: 4, Handle: ffff:0, Parent: ingress, Refcnt: 1}
[tc filter show ingress dev enp3s0f0]
LINK:
&{LinkAttrs:{Index:4 ... Name:enp3s0f0 ... }}
FILTERS: 0

If I use the tc commands that are shown in the square brackets, I obtain what I expected:

# tc qdisc show
...
qdisc clsact ffff: dev eno1 parent ffff:fff1
...
qdisc clsact ffff: dev enp3s0f0 parent ffff:fff1

# tc filter show ingress dev eno1
filter protocol all pref 49152 bpf chain 0
filter protocol all pref 49152 bpf chain 0 handle 0x1 ###.bpf.o:[classifier] direct-action not_in_hw id 3522 tag ### jited
# tc filter show ingress dev enp3s0f0
filter protocol all pref 49152 bpf chain 0
filter protocol all pref 49152 bpf chain 0 handle 0x1 ###.bpf.o:[classifier] direct-action not_in_hw id 3518 tag ### jited