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 kfunc 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). In addition, it's possible to implement relay interface with kfuncs, which can be used with kptrs to "simulate" a new type of map. I'll try it if necessary. This patch set depends on a bugfix patch for relay [2]. I'm working on it to make sure relay map works well. Currently, the selftests could fail without that patch, but it doesn't affect how we use relay map. [0] https://github.com/torvalds/linux/blob/master/Documentation/filesystems/relay.rst [1] https://lore.kernel.org/bpf/20231219122850.433be151@xxxxxxxxxxxxxxxxxx/T/ [2] https://lore.kernel.org/all/20231220074725.23211-1-lulie@xxxxxxxxxxxxxxxxx/ Change logs: v1: - change bpf_relay_output into kfunc instead of helper - refactor relay_map_update_elem to avoid race - add attr->map_extra check in map_alloc - add selftests - other minor bug fixs Philo Lu (3): bpf: implement relay map basis bpf: add bpf_relay_output kfunc selftests/bpf: add bpf relay map selftests include/linux/bpf_types.h | 3 + include/uapi/linux/bpf.h | 7 + kernel/bpf/Makefile | 3 + kernel/bpf/helpers.c | 3 + kernel/bpf/relaymap.c | 221 ++++++++++++++++++ kernel/bpf/syscall.c | 2 + tools/include/uapi/linux/bpf.h | 7 + tools/testing/selftests/bpf/Makefile | 2 +- tools/testing/selftests/bpf/config | 1 + .../selftests/bpf/prog_tests/relay_map.c | 197 ++++++++++++++++ .../selftests/bpf/progs/test_relay_map.c | 69 ++++++ 11 files changed, 514 insertions(+), 1 deletion(-) create mode 100644 kernel/bpf/relaymap.c create mode 100644 tools/testing/selftests/bpf/prog_tests/relay_map.c create mode 100644 tools/testing/selftests/bpf/progs/test_relay_map.c -- 2.32.0.3.g01195cf9f
