[PATCH bpf-next] libbpf: add extra BPF_PROG_TYPE check to bpf_object__probe_loading

[jjedwa165 <jonathan.edwards@165gc.onmicrosoft.com>]

eBPF has been backported for RHEL 7 w/ kernel 3.10-940+ [0]. However 
only the following program types are supported [1]

BPF_PROG_TYPE_KPROBE
BPF_PROG_TYPE_TRACEPOINT
BPF_PROG_TYPE_PERF_EVENT

For libbpf this causes an EINVAL return during the bpf_object__probe_loading
call which only checks to see if programs of type BPF_PROG_TYPE_SOCKET_FILTER
can load.

The following will try BPF_PROG_TYPE_TRACEPOINT as a fallback attempt before 
erroring out. BPF_PROG_TYPE_KPROBE was not a good candidate because on some
kernels it requires knowledge of the LINUX_VERSION_CODE.

[0] https://www.redhat.com/en/blog/introduction-ebpf-red-hat-enterprise-linux-7
[1] https://access.redhat.com/articles/3550581

Signed-off-by: jjedwa165 <jonathan.edwards@165gc.onmicrosoft.com>
---
 tools/lib/bpf/libbpf.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 48c0ade05..1e04ce724 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -4000,6 +4000,10 @@ bpf_object__probe_loading(struct bpf_object *obj)
 	attr.license = "GPL";
 
 	ret = bpf_load_program_xattr(&attr, NULL, 0);
+	if (ret < 0) {
+		attr.prog_type = BPF_PROG_TYPE_TRACEPOINT;
+		ret = bpf_load_program_xattr(&attr, NULL, 0);
+	}
 	if (ret < 0) {
 		ret = errno;
 		cp = libbpf_strerror_r(ret, errmsg, sizeof(errmsg));
-- 
2.17.1