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Date: Wed, 17 Jun 2020 17:51:49 +0200 From: Daniel Borkmann <daniel@...earbox.net> To: Andrii Nakryiko <andrii.nakryiko@...il.com> Cc: Andrii Nakryiko <andriin@...com>, bpf <bpf@...r.kernel.org>, Networking <netdev@...r.kernel.org>, Alexei Starovoitov <ast@...com>, Kernel Team <kernel-team@...com>, Christoph Hellwig <hch@....de> Subject: Re: [PATCH bpf 2/2] selftests/bpf: add variable-length data concatenation pattern test On 6/17/20 1:14 AM, Andrii Nakryiko wrote: > On Tue, Jun 16, 2020 at 3:23 PM Daniel Borkmann <daniel@...earbox.net> wrote: >> On 6/16/20 11:27 PM, Andrii Nakryiko wrote: >>> On Tue, Jun 16, 2020 at 1:21 PM Daniel Borkmann <daniel@...earbox.net> wrote: >>>> On 6/16/20 7:04 AM, Andrii Nakryiko wrote: >>>>> Add selftest that validates variable-length data reading and concatentation >>>>> with one big shared data array. This is a common pattern in production use for >>>>> monitoring and tracing applications, that potentially can read a lot of data, >>>>> but usually reads much less. Such pattern allows to determine precisely what >>>>> amount of data needs to be sent over perfbuf/ringbuf and maximize efficiency. >>>>> >>>>> This is the first BPF selftest that at all looks at and tests >>>>> bpf_probe_read_str()-like helper's return value, closing a major gap in BPF >>>>> testing. It surfaced the problem with bpf_probe_read_kernel_str() returning >>>>> 0 on success, instead of amount of bytes successfully read. >>>>> >>>>> Signed-off-by: Andrii Nakryiko <andriin@...com> >>>> >>>> Fix looks good, but I'm seeing an issue in the selftest on my side. With latest >>>> Clang/LLVM I'm getting: >>>> >>>> # ./test_progs -t varlen >>>> #86 varlen:OK >>>> Summary: 1/0 PASSED, 0 SKIPPED, 0 FAILED >>>> >>>> All good, however, the test_progs-no_alu32 fails for me with: >>> >>> Yeah, same here. It's due to Clang emitting unnecessary bit shifts >>> because bpf_probe_read_kernel_str() is defined as returning 32-bit >>> int. I have a patch ready locally, just waiting for bpf-next to open, >>> which switches those helpers to return long, which auto-matically >>> fixes this test. >>> >>> If it's not a problem, I'd just wait for that patch to go into >>> bpf-next. If not, I can sprinkle bits of assembly magic around to >>> force the kernel to do those bitshifts earlier. But I figured having >>> test_progs-no_alu32 failing one selftest temporarily wasn't too bad. >> >> Given {net,bpf}-next will open up soon, another option could be to take in the fix >> itself to bpf and selftest would be submitted together with your other improvement; >> any objections? > > Yeah, no objections. Sounds good, done.
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