On 6/17/20 1:14 AM, Andrii Nakryiko wrote:
On Tue, Jun 16, 2020 at 3:23 PM Daniel Borkmann <daniel@xxxxxxxxxxxxx> wrote:
On 6/16/20 11:27 PM, Andrii Nakryiko wrote:
On Tue, Jun 16, 2020 at 1:21 PM Daniel Borkmann <daniel@xxxxxxxxxxxxx> 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@xxxxxx>
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.
