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From: Kumar Kartikeya Dwivedi <memxor@gmail.com>
To: bpf@vger.kernel.org
Cc: Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Andrii Nakryiko <andrii@kernel.org>,
Pavel Emelyanov <ovzxemul@gmail.com>,
Alexander Mihalicyn <alexander@mihalicyn.com>,
Andrei Vagin <avagin@gmail.com>, criu@openvz.org,
io-uring@vger.kernel.org, linux-fsdevel@vger.kernel.org
Subject: [PATCH bpf-next v1 0/8] Introduce BPF iterators for io_uring and epoll
Date: Tue, 16 Nov 2021 11:12:29 +0530
Message-Id: <20211116054237.100814-1-memxor@gmail.com>
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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
--
2.33.1