GSoC: retrieve the BTF information

[SuHsueyu]

Hello, I finally located the problem. The tracee process operates the
BPF map object through the BPF virtual file system by using map fd.
When I try to use the BPF syscall with the BPF_OBJ_GET_INFO_BY_FD
subcommand, I need to pass the map_fd associated map object in the
tracer process. But the tracee process holds the map_fd at the same
time. So BPF_OBJ_GET_INFO_BY_FD returns 77, which means "File
descriptor in bad state". Considering BTF retieval generally uses FD,
this is a problem that has to be solved. Do you have any opinion?
Looking forward to your insights on it.