centos man page for journal_lock_updates

JOURNAL_LOCK_UPDATES(9) 				     The Linux Journalling API					   JOURNAL_LOCK_UPDATES(9)

NAME
       journal_lock_updates - establish a transaction barrier.

SYNOPSIS
       void journal_lock_updates(journal_t * journal);

ARGUMENTS
       journal
	   Journal to establish a barrier on.

DESCRIPTION
       This locks out any further updates from being started, and blocks until all existing updates have completed, returning only once the
       journal is in a quiescent state with no updates running.

       We do not use simple mutex for synchronization as there are syscalls which want to return with filesystem locked and that trips up lockdep.
       Also hibernate needs to lock filesystem but locked mutex then blocks hibernation. Since locking filesystem is rare operation, we use simple
       counter and waitqueue for locking.

AUTHORS
       Roger Gammans <rgammans@computer-surgery.co.uk>
	   Author.

       Stephen Tweedie <sct@redhat.com>
	   Author.

COPYRIGHT
Kernel Hackers Manual 3.10					     June 2014						   JOURNAL_LOCK_UPDATES(9)