Parameterize task iterators.

Allow creating an iterator that loops through resources of one task/thread.

People could only create iterators to loop through all resources of
files, vma, and tasks in the system, even though they were interested in only the
resources of a specific task or process.  Passing the addintional
parameters, people can now create an iterator to go through all
resources or only the resources of a task.

Major Changes:

 - Add new parameters in bpf_iter_link_info to indicate to go through
   all tasks or to go through a specific task.

 - Change the implementations of BPF iterators of vma, files, and
   tasks to allow going through only the resources of a specific task.

 - Provide the arguments of parameterized task iterators in
   bpf_link_info.

Differences from v6:

 - Add part 5 to make bpftool show the value of parameters.

 - Change of wording of show_fdinfo() to show pid or tid instead of
   always pid.

 - Simplify error handling and naming of test cases.

Differences from v5:

 - Use user-speace tid/pid terminologies in bpf_iter_link_info and
   bpf_link_info.

 - Fix reference count

 - Merge all variants to one 'u32 pid' in internal structs.
   (bpf_iter_aux_info and bpf_iter_seq_task_common)

 - Compare the result of get_uprobe_offset() with the implementation
   with the vma iterators.

 - Implement show_fdinfo.

Differences from v4:

 - Remove 'type' from bpf_iter_link_info and bpf_link_info.

v6: https://lore.kernel.org/bpf/20220819220927.3409575-1-kuif...
v5: https://lore.kernel.org/bpf/20220811001654.1316689-1-kuif...
v4: https://lore.kernel.org/bpf/20220809195429.1043220-1-kuif...
v3: https://lore.kernel.org/bpf/20220809063501.667610-1-kuife...
v2: https://lore.kernel.org/bpf/20220801232649.2306614-1-kuif...
v1: https://lore.kernel.org/bpf/20220726051713.840431-1-kuife...

Kui-Feng Lee (5):
  bpf: Parameterize task iterators.
  bpf: Handle bpf_link_info for the parameterized task BPF iterators.
  bpf: Handle show_fdinfo for the parameterized task BPF iterators
  selftests/bpf: Test parameterized task BPF iterators.
  bpftool: Show parameters of BPF task iterators.

 include/linux/bpf.h                           |  25 ++
 include/uapi/linux/bpf.h                      |  10 +
 kernel/bpf/task_iter.c                        | 164 ++++++++--
 tools/bpf/bpftool/link.c                      |  19 ++
 tools/include/uapi/linux/bpf.h                |  10 +
 .../selftests/bpf/prog_tests/bpf_iter.c       | 282 ++++++++++++++++--
 .../selftests/bpf/prog_tests/btf_dump.c       |   2 +-
 .../selftests/bpf/progs/bpf_iter_task.c       |   9 +
 .../selftests/bpf/progs/bpf_iter_task_file.c  |   9 +-
 .../selftests/bpf/progs/bpf_iter_task_vma.c   |   7 +-
 .../selftests/bpf/progs/bpf_iter_vma_offset.c |  37 +++
 11 files changed, 526 insertions(+), 48 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/progs/bpf_iter_vma_offset.c

-- 
2.30.2