enabled with the LOCAL_CREDS socket option on the listener. Semantics are
similar to BSD/OS's:
- Creds are available with first data on SOCK_STREAM, and with every datagram
on SOCK_DGRAM.
- It is not possible to forge credentials.
Different in that:
- Different credential data structure (ours does not rely on the format
of internal kernel data structures, and does not pass the login name).
- We can pass creds and file descriptors at the same time (this does not
work in BSD/OS).
Luke Mewburn <lukem@netbsd.org> gets credit for inspiring me to implement
this. :-)
cc22126721