[PATCH v2 bpf-next 0/2] bpf: Add bpf_iter_cpumask

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

Three new kfuncs, namely bpf_iter_cpumask_{new,next,destroy}, have been
added for the new bpf_iter_cpumask functionality. These kfuncs enable the
iteration of percpu data, such as runqueues, system_group_pcpu, and more.

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 the test cases in patch #2 for further context and examples.

Changes:
- v1 -> v2: 
  - Avoid changing cgroup subsystem (Tejun)
  - Remove bpf_cpumask_set_from_pid(), and use bpf_cpumask_copy()
    instead (Tejun)
  - Use `int cpu;` field in bpf_iter_cpumask_kern (Andrii)
- bpf: Add new bpf helper bpf_for_each_cpu
  https://lwn.net/ml/bpf/20230801142912.55078-1-laoar.shao@gmail.com/

Yafang Shao (2):
  bpf: Add bpf_iter_cpumask kfuncs
  selftests/bpf: Add selftests for cpumask iter

 kernel/bpf/cpumask.c                          |  69 +++++++++
 .../selftests/bpf/prog_tests/cpumask_iter.c   | 134 ++++++++++++++++++
 .../selftests/bpf/progs/cpumask_common.h      |   3 +
 .../selftests/bpf/progs/test_cpumask_iter.c   |  62 ++++++++
 4 files changed, 268 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/cpumask_iter.c
 create mode 100644 tools/testing/selftests/bpf/progs/test_cpumask_iter.c

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