From rusty:

From rusty:

Subject: eventscript: fix spinning at 100% cpu when child exits.

ctdbd was spinning reading 0 from a pipe, as soon as the first
eventscript finishes.

This was caused by the intersection between a78b8ea7168e "Run only one
event for each epoll_wait/select call" and 32cfdc3aec34 "eventscript:
ctdb_fork_with_logging()".  Unavoidable mid-air collision, since both
worked fine and both were developed simultaneously.

When the script exits, we have two pipes open to it: one for any
stdout/stderr for logging (ctdb_log_handler), and one for the result
(ctdb_event_script_handler).  The latter frees everything, including
the log fd and event structure.

We used to get one callback to ctdb_log_handler, which got a harmless
0-length read, then one to ctdb_event_script_handler which cleaned up.
Now we only do one callback per poll, we need the logging function to
clean itself up so we can make process.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>