> On Nov 19, 2021, at 3:14 PM, Andrii Nakryiko <andrii@xxxxxxxxxx> wrote:
>
> Add selftest that combines two BPF programs within single BPF object
> file such that one of the programs is using global variables, but can be
> skipped at runtime on old kernels that don't support global data.
> Another BPF program is written with the goal to be runnable on very old
> kernels and only relies on explicitly accessed BPF maps.
>
> Such test, run against old kernels (e.g., libbpf CI will run it against 4.9
> kernel that doesn't support global data), allows to test the approach
> and ensure that libbpf doesn't make unnecessary assumption about
> necessary kernel features.
>
> Signed-off-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
Acked-by: Song Liu <songliubraving@xxxxxx>
With one nit below.
> ---
> .../selftests/bpf/prog_tests/legacy_printk.c | 65 +++++++++++++++++++
> .../selftests/bpf/progs/test_legacy_printk.c | 65 +++++++++++++++++++
> 2 files changed, 130 insertions(+)
> create mode 100644 tools/testing/selftests/bpf/prog_tests/legacy_printk.c
> create mode 100644 tools/testing/selftests/bpf/progs/test_legacy_printk.c
>
[...]
> +SEC("tp/raw_syscalls/sys_enter")
> +int handle_legacy(void *ctx)
> +{
> + int zero = 0, *my_pid, cur_pid, *my_res;
> +
> + my_pid = bpf_map_lookup_elem(&my_pid_map, &zero);
> + if (!my_pid)
> + return 1;
> +
> + cur_pid = bpf_get_current_pid_tgid() >> 32;
> + if (cur_pid != *my_pid)
> + return 1;
> +
> + my_res = bpf_map_lookup_elem(&res_map, &zero);
> + if (!my_res)
> + return 1;
> +
> + if (*my_res == 0)
> + bpf_printk("Legacy-case bpf_printk test, pid %d\n", cur_pid);
I think we discourage bpf_printk in selftests in general, but we do need the
bpf_printk here. So maybe add a comment here (and below) to explain the case?
Thanks,
Song
> + *my_res = 1;
> +
> + return *my_res;
> +}
> +
> +SEC("tp/raw_syscalls/sys_enter")
> +int handle_modern(void *ctx)
> +{
> + int zero = 0, cur_pid;
> +
> + cur_pid = bpf_get_current_pid_tgid() >> 32;
> + if (cur_pid != my_pid_var)
> + return 1;
> +
> + if (res_var == 0)
> + bpf_printk("Modern-case bpf_printk test, pid %d\n", cur_pid);
> + res_var = 1;
> +
> + return res_var;
> +}
> --
> 2.30.2
>
