On 6/16/20 11:27 PM, Andrii Nakryiko wrote:
On Tue, Jun 16, 2020 at 1:21 PM Daniel Borkmann <[email protected]> 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 <[email protected]>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?
Thanks,
Daniel
