I'm supervising an instance of an X Server using s6. X.Org has a built-in readiness notification mechanism: it sends a USR1 to its parent process once it's ready. From what I know, it would be s6-supervise.
However, after reading the documentation, there doesn't seem to be a way to set up custom USR1 handlers for s6-supervise. As far as I know, this leaves me with two, not quite ideal solutions: make the run script spawn X and do readiness notification on its behalf (which lengthens the supervision chain), or poll it (which is what I've been doing). Is there a way to not let the information from this USR1 not "go to waste"? Forgive me if I'm not seeing an obvious solution for this problem that doesn't involve patching either software.