lib: rewrite zlog lock-free & TLS-buffered

This is a full rewrite of the "back end" logging code.  It now uses a
lock-free list to iterate over logging targets, and the targets
themselves are as lock-free as possible.  (syslog() may have a hidden
internal mutex in the C library;  the file/fd targets use a single
write() call which should ensure atomicity kernel-side.)

Note that some functionality is lost in this patch:
- Solaris printstack() backtraces are ditched (unlikely to come back)
- the `log-filter` machinery is gone (re-added in followup commit)
- `terminal monitor` is temporarily stubbed out.  The old code had a
  race condition with VTYs going away.  It'll likely come back rewritten
  and with vtysh support.
- The `zebra_ext_log` hook is gone.  Instead, it's now much easier to
  add a "proper" logging target.

v2: TLS buffer to get some actual performance

Signed-off-by: David Lamparter <equinox@diac24.net>

1 files changed, 1 insertions, 0 deletions

diff --git a/lib/thread.c b/lib/thread.c
index dbf668a699..4d689a9f88 100644
--- a/lib/thread.c
+++ b/lib/thread.c
@@ -724,6 +724,7 @@ static int fd_poll(struct thread_master *m, struct pollfd *pfds, nfds_t pfdsize,
 		 < 0) // effect a poll (return immediately)
 		timeout = 0;
 
+	zlog_tls_buffer_flush();
 	rcu_read_unlock();
 	rcu_assert_read_unlocked();