[PATCH v3 bpf-next 0/2] bpf: Add a generic bits iterator

[Yafang Shao <laoar.shao@gmail.com>]

Three new kfuncs, namely bpf_iter_bits_{new,next,destroy}, have been
added for the new bpf_iter_bits functionality. These kfuncs enable the
iteration of the bits from a given address and a given number of bits.

- bpf_iter_bits_new
  Initialize a new bits iterator for a given memory area. Due to the
  limitation of bpf memalloc, the max number of bits to be iterated
  over is (4096 * 8).
- bpf_iter_bits_next
  Get the next bit in a bpf_iter_bits
- bpf_iter_bits_destroy
  Destroy a bpf_iter_bits

The bits iterator can be used in any context and on any address.

In our specific use case, we leverage the cgroup iterator to traverse
percpu data, subsequently exposing it to userspace through a seq file.
Refer to example in patch #2 for the usage.

Changes:
- v2->v3:
  - Optimization for u64/u32 mask (Andrii)
- v1->v2:
  - Simplify the CPU number verification code to avoid the failure on s390x
    (Eduard)
- bpf: Add bpf_iter_cpumask
  https://lwn.net/Articles/961104/
- bpf: Add new bpf helper bpf_for_each_cpu
  https://lwn.net/Articles/939939/


Yafang Shao (2):
  bpf: Add bits iterator
  selftests/bpf: Add selftest for bits iter

 kernel/bpf/helpers.c                          | 117 +++++++++++++++
 tools/testing/selftests/bpf/DENYLIST.s390x    |   3 +-
 .../selftests/bpf/prog_tests/bits_iter.c      | 137 ++++++++++++++++++
 .../bpf/progs/test_bits_iter_failure.c        |  54 +++++++
 .../bpf/progs/test_bits_iter_success.c        | 122 ++++++++++++++++
 5 files changed, 432 insertions(+), 1 deletion(-)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/bits_iter.c
 create mode 100644 tools/testing/selftests/bpf/progs/test_bits_iter_failure.c
 create mode 100644 tools/testing/selftests/bpf/progs/test_bits_iter_success.c

-- 
2.39.1