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

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

On 2023/12/22 22:45, Jiri Olsa wrote:
> On Fri, Dec 22, 2023 at 08:21:43PM +0800, Philo Lu wrote:
>> 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.
> 
> looks useful, selftests might be already helpful to see the usage
> 

Ok, I will add selftests in the next version.

Thanks.

> jirka
> 
>>
>> [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
>>