A new field has been added to Ndb to mark the file as open.

Reference: /n/patches.lsub.org/patch/ndbreopen
Date: Mon Jul  2 18:34:10 CES 2012
Signed-off-by: esoriano@lsub.org

--- /sys/src/libndb/ndbopen.c	Thu Apr 12 12:26:24 2012
+++ /sys/src/libndb/ndbopen.c	Mon Jul  2 17:58:33 2012
@@ -90,12 +90,13 @@
 	Dir *d;
 
 	/* forget what we know about the open files */
-	if(db->mtime){
+	if(db->isopen){
 		_ndbcacheflush(db);
 		hffree(db);
 		close(Bfildes(&db->b));
 		Bterm(&db->b);
 		db->mtime = 0;
+		db->isopen = 0;
 	}
 
 	/* try the open again */
@@ -111,6 +112,7 @@
 	db->qid = d->qid;
 	db->mtime = d->mtime;
 	db->length = d->length;
+	db->isopen = 1;
 	Binits(&db->b, fd, OREAD, db->buf, sizeof(db->buf));
 	free(d);
 	return 0;
--- /sys/include/ndb.h	Thu Apr 12 12:24:41 2012
+++ /sys/include/ndb.h	Mon Jul  2 17:26:25 2012
@@ -33,6 +33,7 @@
 	Qid		qid;		/* qid of db file */
 	char		file[128];/* path name of db file */
 	ulong		length;		/* length of db file */
+	int		isopen;	/* true if the file is open */
 
 	int		nohash;		/* don't look for hash files */
 	Ndbhf		*hf;		/* open hash files */