[bpf-next,v1,0/8] Introduce BPF iterators for io_uring and epoll

Message

Kumar Kartikeya Dwivedi Nov. 16, 2021, 5:42 a.m. UTC

The CRIU [0] project developers are exploring potential uses of the BPF
 subsystem to do complicated tasks that are difficult to add support for in the
 kernel using existing interfaces.  Even if they are implemented using procfs,
 or kcmp, it is difficult to make it perform well without having some kind of
 programmable introspection into the kernel data structures. Moreover, for
 procfs based state inspection, the output format once agreed upon is set in
 stone and hard to extend, and at the same time inefficient to consume from
 programs (where it is first converted from machine readable form to human
 readable form, only to be converted again to machine readable form).  In
 addition to this, kcmp based file set matching algorithm performs poorly since
 each file in one set needs to be compared to each file in another set, to
 determine struct file equivalence.

 This set adds a io_uring file iterator (for registered files), a io_uring ubuf
 iterator (for registered buffers), and a epoll iterator (for registered items
 (files, registered using EPOLL_CTL_ADD)) to overcome these limitations.  Using
 existing task, task_file, task_vma iterators, all of these can be combined
 together to significantly enhance and speed up the task dumping procedure.

 The two immediate use cases are io_uring checkpoint/restore support and epoll
 checkpoint/restore support. The first is unimplemented, and the second is being
 expedited using a new epoll iterator. In the future, more stages of the
 checkpointing sequence can be offloaded to eBPF programs to reduce process
 downtime, e.g. in pre-dump stage, before task is seized.

 The io_uring file iterator is even more important now due to the advent of
 descriptorless files in io_uring [1], which makes dumping a task's files a lot
 more harder for CRIU, since there is no visibility into these hidden
 descriptors that the task depends upon for operation. Similarly, the
 io_uring_ubuf iterator is useful in case original VMA used in registering a
 buffer has been destroyed.

 Please see the individual patches for more details.

   [0]: https://criu.org/Main_Page
   [1]: https://lwn.net/Articles/863071

Kumar Kartikeya Dwivedi (8):
  io_uring: Implement eBPF iterator for registered buffers
  bpf: Add bpf_page_to_pfn helper
  io_uring: Implement eBPF iterator for registered files
  epoll: Implement eBPF iterator for registered items
  selftests/bpf: Add test for io_uring BPF iterators
  selftests/bpf: Add test for epoll BPF iterator
  selftests/bpf: Test partial reads for io_uring, epoll iterators
  selftests/bpf: Fix btf_dump test for bpf_iter_link_info

 fs/eventpoll.c                                | 196 +++++++++-
 fs/io_uring.c                                 | 334 ++++++++++++++++
 include/linux/bpf.h                           |   6 +
 include/uapi/linux/bpf.h                      |  15 +
 kernel/trace/bpf_trace.c                      |   2 +
 scripts/bpf_doc.py                            |   2 +
 tools/include/uapi/linux/bpf.h                |  15 +
 .../selftests/bpf/prog_tests/bpf_iter.c       | 362 +++++++++++++++++-
 .../selftests/bpf/prog_tests/btf_dump.c       |   4 +-
 .../selftests/bpf/progs/bpf_iter_epoll.c      |  33 ++
 .../selftests/bpf/progs/bpf_iter_io_uring.c   |  50 +++
 11 files changed, 1015 insertions(+), 4 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/progs/bpf_iter_epoll.c
 create mode 100644 tools/testing/selftests/bpf/progs/bpf_iter_io_uring.c