[PATCH bpf-next 0/3] bpf: introduce BPF_MAP_TYPE_RELAY

[Philo Lu <lulie@linux.alibaba.com>]

The patch set introduce a new type of map, BPF_MAP_TYPE_RELAY, based on
relay interface [0]. It provides a way for persistent and overwritable data
transfer.

As stated in [0], relay is a efficient method for log and data transfer.
And the interface is simple enough so that we can implement and use this
type of map with current map interfaces. Besides we need a new helper
bpf_relay_output to output data to user, similar with bpf_ringbuf_output.

We need this map because currently neither ringbuf nor perfbuf satisfies
the requirements of relatively long-term consistent tracing, where the bpf
program keeps writing into the buffer without any bundled reader, and the
buffer supports overwriting. For users, they just run the bpf program to
collect data, and are able to read as need. The detailed discussion can be
found at [1].

The buffer is exposed to users as per-cpu files in debugfs, supporting read
and mmap, and it is up to users how to formulate and read it, either
through a program with mmap or just `cat`. Specifically, the files are
created as "/sys/kerenl/debug/<dirname>/<mapname>#cpu", where the <dirname>
is defined with map_update_elem (Note that we do not need to implement
actual elem operators for relay_map).

If this map is acceptable, other parts including docs, libbpf support,
selftests, and benchmarks (if need) will be added in the following version.

[0]
https://github.com/torvalds/linux/blob/master/Documentation/filesystems/relay.rst
[1]
https://lore.kernel.org/bpf/20231219122850.433be151@gandalf.local.home/T/

Philo Lu (3):
  bpf: implement relay map basis
  bpf: implement map_update_elem to init relay file
  bpf: introduce bpf_relay_output helper

 include/linux/bpf.h       |   1 +
 include/linux/bpf_types.h |   3 +
 include/uapi/linux/bpf.h  |  17 +++
 kernel/bpf/Makefile       |   3 +
 kernel/bpf/helpers.c      |   4 +
 kernel/bpf/relaymap.c     | 213 ++++++++++++++++++++++++++++++++++++++
 kernel/bpf/syscall.c      |   1 +
 kernel/bpf/verifier.c     |   8 ++
 kernel/trace/bpf_trace.c  |   4 +
 9 files changed, 254 insertions(+)
 create mode 100644 kernel/bpf/relaymap.c

--
2.32.0.3.g01195cf9f