update(8) is gone, put in some info about ioflush

this addresses bin/11141 by Nick Hudson

lib/libc/sys/sync.2

@@ -1,4 +1,4 @@
-.\"	$NetBSD: sync.2,v 1.7 1999/12/02 21:42:40 kleink Exp $
+.\"	$NetBSD: sync.2,v 1.8 2000/10/06 19:54:26 jdolecek Exp $
 .\"
 .\" Copyright (c) 1980, 1991, 1993
 .\"	The Regents of the University of California.  All rights reserved.
@@ -52,13 +52,15 @@ function forces a write of dirty (modified) buffers
 in the block buffer cache out
 to disk. The kernel keeps this information in core to reduce
 the number of disk I/O transfers required by the system.
-As information in the cache is lost after a system crash a
-.Fn sync
-call is issued
-frequently
-by the user process
-.Xr update 8
-(about every 30 seconds). 
+As information in the cache is lost after a system crash,
+kernel thread
+.Nm ioflush
+ensures that dirty buffers are synced to disk
+eventually. By default, a dirty buffer is synced after 30 seconds,
+but some filesystems exploit
+.Nm ioflush
+features to sync directory data and metadata faster
+(after 15 and 10 seconds, respectively).
 .Pp
 The function
 .Xr fsync 2
@@ -66,8 +68,7 @@ may be used to synchronize individual file descriptor
 attributes.
 .Sh SEE ALSO
 .Xr fsync 2 ,
-.Xr sync 8 ,
-.Xr update 8
+.Xr sync 8
 .Sh BUGS
 .Fn sync
 may return before the buffers are completely flushed.