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@xxxxxxxxxxxxxxxxxx/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
