netdev - Re: [PATCH bpf-next v2 0/6] skip verifier/map tests if kernel support is missing

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Message-ID: <14aaab6c-e4a3-ae78-a121-1d9a5fc217d6@iogearbox.net>
Date:   Wed, 19 Dec 2018 00:18:07 +0100
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Stanislav Fomichev <sdf@...ichev.me>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     Stanislav Fomichev <sdf@...gle.com>, netdev@...r.kernel.org,
        ast@...nel.org, davem@...emloft.net, ecree@...arflare.com,
        quentin.monnet@...ronome.com
Subject: Re: [PATCH bpf-next v2 0/6] skip verifier/map tests if kernel support
 is missing

On 12/18/2018 10:30 PM, Stanislav Fomichev wrote:
> On 12/18, Alexei Starovoitov wrote:
>> On Mon, Dec 17, 2018 at 10:25:48AM -0800, Stanislav Fomichev wrote:
>>> If test_maps/test_verifier is running against the kernel which doesn't
>>> have _all_ BPF features enabled, it fails with an error. This patch
>>> series tries to probe kernel support for each failed test and skip
>>> it instead. This lets users run BPF selftests in the not-all-bpf-yes
>>> environments and received correct PASS/NON-PASS result.
>>>
>>> See https://www.spinics.net/lists/netdev/msg539331.html for more
>>> context.
>>>
>>> The series goes like this:
>>>
>>> * patch #1 adds bpf_prog_type_supported() and
>>>   bpf_map_type_supported() which query the kernel (insert 'return 0'
>>>   program or try to create empty map with correct key/value sizes) and
>>>   return supported/unsupported.
>>>   Note: this functionality can later be reimplemented on top of Quentin's
>>>   recent 'bpftool feature' patchset if he decides to move the probes
>>>   into libbpf.
>>> * patch #2 skips sockmap tests in test_maps.c if BPF_MAP_TYPE_SOCKMAP
>>>   map is not supported (if bpf_create_map fails, we probe the kernel
>>>   for support)
>>> * patch #3 skips verifier tests if test->prog_type is not supported (if
>>>   bpf_verify_program fails, we probe the kernel for support)
>>> * patch #4 skips verifier tests if test fixup map is not supported (if
>>>   create_map fails, we probe the kernel for support)
>>>   Note: we can probably move this probe into create_map helper and
>>>   return some argument instead of adding skip_unsupported_map()
>>>   to each fixup; but I'm not sure it's better.
>>>   Also note: in current implementation we still print 'Failed to
>>>   create hash map' from the create_map, but still skip the test.
>>> * next patches fix various small issues that arise from the first four:
>>>   * patch #5 sets "unknown func bpf_trace_printk#6" prog_type to
>>>     BPF_PROG_TYPE_TRACEPOINT so it is correctly skipped in
>>>     CONFIG_BPF_EVENTS=n case
>>>   * patch #6 exposes BPF_PROG_TYPE_CGROUP_{SKB,SOCK,SOCK_ADDR} only when
>>>     CONFIG_CGROUP_BPF=y, this makes verifier correctly skip appropriate
>>>     tests
>>>
>>> v2 changes:
>>>
>>> * don't sprinkle "ifdef CONFIG_CGROUP_BPF" all around net/core/filter.c,
>>>   doing it only in the bpf_types.h is enough to disable
>>>   BPF_PROG_TYPE_CGROUP_{SKB,SOCK,SOCK_ADDR} prog types for non-cgroup
>>>   enabled kernels
>>
>> the patches look good to me.
>> I think it's ok to proceed this way though long term we probably
>> want to have such bpf_prog_type_supported() to be part of libbpf
>> and reused in test_verifier.c and in bpftool.
> Quentin is working on adding more generic bpf_xyz_type_supported() to
> libbpf. My plan is to switch to them as soon as they are merged.

Yeah, libbpf probes in-tree user for BPF kselftest sounds good to me.

>> Daniel, thoughts?

I just have few minor nits; will reply in a sec to the two patches, but
it's nothing blocking the series here.

Thanks,
Daniel