Rewrite linux helper iterators in C

[ghost]

This was split off from #129 per @osandov's request.

In preparation for introducing an API to represent threads, the linux
helper iterators, radix_tree_for_each, idr_for_each, for_each_pid, and
for_each_task have been rewritten in C. This will allow them to be
accessed from libdrgn, which will be necessary for the threads API.

Signed-off-by: Kevin Svetlitski [email protected]

[ghost]

@osandov All of your comments on the iterator implementations have been addressed here, this PR is ready for review.

[osandov]

Just a few trivial things. Are those test failures in your temporary test just because the vmtest environment doesn't have many processes? Once you get rid of the temporary shims, I'll just clean up trivial code style issues myself (I wish clang-format was usable for the Linux kernel style).

[ghost]

Just a few trivial things. Are those test failures in your temporary test just because the vmtest environment doesn't have many processes? Once you get rid of the temporary shims, I'll just clean up trivial code style issues myself (I wish clang-format was usable for the Linux kernel style).

The failures are because we now iterate the pid_hash in a different order. FWIW, I've been using clang-format thus far with very little manual tweaking necessary.

[osandov]

This is the failure I'm referring to:

======================================================================
FAIL: test_for_each_pid (tests.helpers.linux.test_c_helpers.TestCHelpers)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/runner/work/drgn/drgn/tests/helpers/linux/test_c_helpers.py", line 24, in test_for_each_pid
    self.verify_iterators_match(old_for_each_pid, for_each_pid, self.prog)
  File "/home/runner/work/drgn/drgn/tests/helpers/linux/test_c_helpers.py", line 17, in verify_iterators_match
    self.assertTrue(sum(1 for _ in old_iter(arg)) >= 100)
AssertionError: False is not true

[ghost]

Alright, temporary shims have been removed, and everything has been combined into a single commit.

[ghost]

This is the failure I'm referring to:

======================================================================
FAIL: test_for_each_pid (tests.helpers.linux.test_c_helpers.TestCHelpers)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/runner/work/drgn/drgn/tests/helpers/linux/test_c_helpers.py", line 24, in test_for_each_pid
    self.verify_iterators_match(old_for_each_pid, for_each_pid, self.prog)
  File "/home/runner/work/drgn/drgn/tests/helpers/linux/test_c_helpers.py", line 17, in verify_iterators_match
    self.assertTrue(sum(1 for _ in old_iter(arg)) >= 100)
AssertionError: False is not true

I would assume so yes, as old_iter is the pure-Python implementation that you wrote, and I didn't touch those so I don't know how that would be broken.

[ghost]

I'll fix the isort real quick

[osandov]

I just pushed to make isort and black happy. Once those tests all pass, I'll merge this.