Re: [PATCH 0/3] bpf: allow zero-initialising hash map seed

On Mon, 1 Oct 2018 at 20:12, Daniel Borkmann [off-list ref] wrote:

On 10/01/2018 12:45 PM, Lorenz Bauer wrote:

quoted

This patch set adds a new flag BPF_F_ZERO_SEED, which allows
forcing the seed used by hash maps to zero. This makes
it possible to write deterministic tests.

Based on an off-list conversation with Alexei Starovoitov and
Daniel Borkmann.

Lorenz Bauer (3):
  bpf: allow zero-initializing hash map seed
  tools: sync linux/bpf.h
  tools: add selftest for BPF_F_ZERO_SEED

 include/uapi/linux/bpf.h                |  2 +
 kernel/bpf/hashtab.c                    |  8 ++-
 tools/include/uapi/linux/bpf.h          |  2 +
 tools/testing/selftests/bpf/test_maps.c | 67 +++++++++++++++++++++----
 4 files changed, 66 insertions(+), 13 deletions(-)

Please respin with proper SoB for each patch and non-empty commit
description.

What does SoB mean? Point taken about the empty commit message.

I think patch 1 should also have a more elaborate
commit description on the use case for BPF_F_ZERO_SEED, and I

This came out of the off-list discussion we had about map hash functions,
where Alexei expressed concern that your change to randomise the seed
might catch users off-guard. I personally don't have a use case, but decided
to tackle it since it seemed a simple-ish fix to get acquainted with
the code base.

Maybe this isn't needed after all?

think also a better comment in the uapi header that this is only
meant for testing and not production use.

Will do, if you decide that this is worth having in the first place.

Thanks,
Daniel

Lorenz

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Lorenz Bauer  |  Systems Engineer
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