perf test bpf on older kernels

[Arnaldo Carvalho de Melo <acme@kernel.org>]

Hi Wang,

	While testing on a machine with an older kernel I noticed this:

[root@felicio ~]# perf test bpf
37: Test BPF filter                                          :
37.1: Test basic BPF filtering                               : FAILED!
37.2: Test BPF prologue generation                           : Skip
[root@felicio ~]#

symsrc__init: cannot get elf header.
Using /proc/kcore for kernel object code
Using /proc/kallsyms for symbols
Opening /sys/kernel/debug/tracing//kprobe_events write=1
Writing event: p:perf_bpf_probe/func _text+2266976
libbpf: failed to create map: Function not implemented
libbpf: failed to load object '[basic_bpf_test]'
bpf: load objects failed
Failed to add events selected by BPF
Opening /sys/kernel/debug/tracing//kprobe_events write=1
Opening /sys/kernel/debug/tracing//uprobe_events write=1
Parsing probe_events: p:perf_bpf_probe/func _text+2266976
Group:perf_bpf_probe Event:func probe:p
Writing event: -:perf_bpf_probe/func
test child finished with -1
---- end ----
Test BPF filter subtest 0: FAILED!
37.2: Test BPF prologue generation                           :
--- force skipped ---
Test BPF filter subtest 1: Skip
[root@felicio ~]# 

So what happens is that the kernel doesn't have the feature you're
trying to test, I think in this case the test should just pass with
"Skip", not FAILED, that should be reserved for kernel tests for when
the kernel supports a feature that then fails to work as advertised, ok?

- Arnaldo