MAKEDEV_CHECKNAME flag to the call, this is required to not panic on
race between the clone and destructing the closed master.
Reported by and discussed with: bde
Tested by: pho (as part of the larger patch)
Sponsored by: The FreeBSD Foundation
MFC after: 3 weeks
Now that pty(4) is a loadable kernel module, I'd better move /dev/ptmx
in there as well. This means that pty(4) now provides almost all
pseudo-terminal compatibility code. This means it's very easy to test
whether applications use the proper library interfaces when allocating
pseudo-terminals (namely posix_openpt and openpty).
Unfortunately, the wrappers that are present in pts(4) don't have the
mechanics to allow pty(4) to be unloaded safely, so I'm forcing this kld
to return EBUSY. This also means we have to enable some extra code in
pts(4) unconditionally.
Proposed by: rwatson
