Merge branch 'bpf_iter-fixes'

Yonghong Song says:

====================
Commit ae24345da54e ("bpf: Implement an interface to register
bpf_iter targets") and its subsequent commits in the same patch set
introduced bpf iterator, a way to run bpf program when iterating
kernel data structures.

This patch set addressed some followup issues. One big change
is to allow target to pass ctx arg register types to verifier
for verification purpose. Please see individual patch for details.

Changelogs:
  v1 -> v2:
    . add "const" qualifier to struct bpf_iter_reg for
      bpf_iter_[un]reg_target, and this results in
      additional "const" qualifiers in some other places
    . drop the patch which will issue WARN_ONCE if
      seq_ops->show() returns a positive value.
      If this does happen, code review should spot
      this or author does know what he is doing.
      In the future, we do want to implement a
      mechanism to find out all registered targets
      so we will be aware of new additions.
====================

Acked-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>