set_child_subreaper: What's the pid argument supposed to do?

[rusty-snake]

The kernel knows for set_child_subreaper only poor man boolean (int == 0/!= 0).

[sunfishcode]

Indeed, that looks like an error. It should be a bool rather than an Option<Pid>. We should deprecate child_subreaper and set_child_subreaper and add new functions with the correct types.