A guest kqueue and a guest /dev/urandom are /dev/null placeholders with
their behaviour in libkernel's tables, and a guest directory descriptor
keeps its reading state there too. sendmsg sent the placeholder, and the
receiver got a descriptor that failed kevent or read as empty. FreeBSD's
unp_internalize returns EOPNOTSUPP for a kqueue (no DFLAG_PASSABLE), so a
kqueue now gets that; a random device or a directory throws.
A zero-byte sendmsg carrying descriptors on a stream socket returned 0
and lost them, as Linux sends no record without data. It throws now.
FreeBSD sends the control data alone there.
guest_socket_rights checks the kqueue refusal and that the next send on
the pair arrives without control data.
Co-Authored-By: Claude Opus 5.5 <[email protected]>
