libbpf: Move BPF_SEQ_PRINTF and BPF_SNPRINTF to bpf_helpers.h

These macros are convenient wrappers around the bpf_seq_printf and
bpf_snprintf helpers. They are currently provided by bpf_tracing.h which
targets low level tracing primitives. bpf_helpers.h is a better fit.

The __bpf_narg and __bpf_apply are needed in both files and provided
twice. __bpf_empty isn't used anywhere and is removed from bpf_tracing.h

Reported-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Florent Revest <revest@chromium.org>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20210526164643.2881368-1-revest@chromium.org

samples/bpf, selftests/bpf: Use bpf_probe_read_kernel

A handful of samples and selftests fail to build on s390, because
after commit 0ebeea8ca8a4 ("bpf: Restrict bpf_probe_read{, str}()
only to archs where they work") bpf_probe_read is not available
anymore.

Fix by using bpf_probe_read_kernel.

Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200720114806.88823-1-iii@linux.ibm.com

selftests/bpf: Implement sample udp/udp6 bpf_iter programs

On my VM, I got identical results between /proc/net/udp[6] and
the udp{4,6} bpf iterator.

For udp6:
$ cat /sys/fs/bpf/p1
sl local_address remote_address st tx_queue rx_queue tr tm->when retrnsmt uid timeout inode ref pointer drops
1405: 000080FE00000000FF7CC4D0D9EFE4FE:0222 00000000000000000000000000000000:0000 07 00000000:00000000 00:00000000 00000000 193 0 19183 2 0000000029eab111 0
$ cat /proc/net/udp6
sl local_address remote_address st tx_queue rx_queue tr tm->when retrnsmt uid timeout inode ref pointer drops
1405: 000080FE00000000FF7CC4D0D9EFE4FE:0222 00000000000000000000000000000000:0000 07 00000000:00000000 00:00000000 00000000 193 0 19183 2 0000000029eab111 0

For udp4:
$ cat /sys/fs/bpf/p4
sl local_address rem_address st tx_queue rx_queue tr tm->when retrnsmt uid timeout inode ref pointer drops
2007: 00000000:1F90 00000000:0000 07 00000000:00000000 00:00000000 00000000 0 0 72540 2 000000004ede477a 0
$ cat /proc/net/udp
sl local_address rem_address st tx_queue rx_queue tr tm->when retrnsmt uid timeout inode ref pointer drops
2007: 00000000:1F90 00000000:0000 07 00000000:00000000 00:00000000 00000000 0 0 72540 2 000000004ede477a 0

Signed-off-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Link: https://lore.kernel.org/bpf/20200623230822.3989299-1-yhs@fb.com