Details:
- The main thread runs editline(3) functions, that can block.
- A separate thread is launched to monitor netgraph sockets.
- The access to the descriptors is protected by a mutex. At
runtime the monitoring thread owns the mutex. When the main
thread reads a command from el_gets() it asks the monitoring
thread to release a mutex and sleep until the main thread
processes the command.
This makes ngctl(8) depend on libedit, and libpthread. Thus, the
new functionality isn't compiled in if release is being built
with -DRELEASE_CRUNCH.
PR: bin/87352
Reviewed by: ru, Nuno Antunes <nuno.antunes gmail.com>
b9124a7354