proposal: os/signal: relay POSIX signal values

[xry111]

POSIX signal values (union sigval) is an application defined extra parameter of signals. It could be
delivered by sigqueue, or timer_create etc. In some situations this is very useful. But now we can't get it in Go. I've tried to implement this as an external package but it seems impossible.

[rsc]

This really doesn't fit into os/signal. It doesn't seem impossible, though: if you really need to handle that information you can use cgo to register a signal handler in C and handle those from the C side.

[xry111]

Thanks for the suggestion. I'll use cgo to do that.