From 2ded039a6da22e85917388ed0b611e4858d05a72 Mon Sep 17 00:00:00 2001 From: trasz Date: Sun, 31 Aug 2014 21:51:01 +0000 Subject: MFC r270399: Add comment explaining one of the quirks in autofs. Sponsored by: The FreeBSD Foundation --- sys/fs/autofs/autofs.c | 8 ++++++++ 1 file changed, 8 insertions(+) (limited to 'sys/fs/autofs/autofs.c') diff --git a/sys/fs/autofs/autofs.c b/sys/fs/autofs/autofs.c index d3ea03d..d5a6892 100644 --- a/sys/fs/autofs/autofs.c +++ b/sys/fs/autofs/autofs.c @@ -595,6 +595,14 @@ autofs_open(struct cdev *dev, int flags, int fmt, struct thread *td) { sx_xlock(&sc->sc_lock); + /* + * We must never block automountd(8) and its descendants, and we use + * session ID to determine that: we store session id of the process + * that opened the device, and then compare it with session ids + * of triggering processes. This means running a second automountd(8) + * instance would break the previous one. The check below prevents + * it from happening. + */ if (sc->sc_dev_opened) { sx_xunlock(&sc->sc_lock); return (EBUSY); -- cgit v1.1