Hello Alan,
On 8/1/24 10:17, Alan Maguire wrote:
On 31/07/2024 19:53, Alexis Lothoré wrote:
Hello Alan,
On 7/31/24 19:23, Alan Maguire wrote:
On 31/07/2024 11:38, Alexis Lothoré (eBPF Foundation) wrote:
[...]
- pid = getpid();
- if (!ASSERT_OK(bpf_map__update_elem(skel->maps.pidmap, &key,
sizeof(key), &pid, sizeof(pid), 0),"write pid"))goto cleanup_progs;I think it would be worth using a global variable in the BPF program my_pid, and setting skel->bss->my_pid here as other more up-to-date tests do (example progs/test_usdt.c, prog_tests/usdt.c). No need for a separate map anymore.
That sounds like a good improvement, thanks for the hint and the example :) I'll spin a new revision with this, and make sure to use it in my next test conversion patches too when relevant.
TBH I am not familiar with global variables usage in ebpf/libbpf, so it is not clear for me when I should prefer it over classic maps. From some quick search I feel like it should be the default choice when needing basic controls knobs/feedback on a bpf program from userspace ? Or maybe it should be used even more broadly by default ?
Yeah, it's certainly what I use by default, unless I need multiple instances of an object. Under the hood, the BPF skeleton creates single-element array maps for .bss, .data and .rodata sections which contain all the initialized, uninitialized and constant globals in the BPF object and mmaps() them so you can read/update the values in userspace via skel->bss/skel->data without needing a map-related syscalls.
Thanks a lot for the additional details, much appreciated :)