Hi Martin,

During the testing of bpf_tcp_ca, I found that if the test program
aborts before calling bpf_link__detach_struct_ops(), the registered
bpf_dctcp will not be unregistered, and running bpf_tcp_ca test again
will fail with -EEXIST error as shown below:

test_dctcp:PASS:bpf_dctcp__open_and_load 0 nsec
test_dctcp:FAIL:bpf_map__attach_struct_ops unexpected error: -17

The root cause is that the release of BPF_MAP_TYPE_STRUCT_OPS fd
neither put struct_ops programs in maps nor unregister the struct_ops
from kernel. Was the implementation intentional, or was it an oversight ?
If it is an oversight, I will post a patch to fix it.

Regards,
Tao