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From: Konstantin Belousov <kib@FreeBSD.org>
Date: Wed, 29 Feb 2012 15:18:53 +0000 (UTC)
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Subject: svn commit: r232305 - head/sys/fs/nullfs
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Author: kib
Date: Wed Feb 29 15:18:53 2012
New Revision: 232305
URL: http://svn.freebsd.org/changeset/base/232305

Log:
  Allow shared locks for reads when lower filesystem accept shared locking.
  
  Tested by:	pho
  MFC after:	1 week

Modified:
  head/sys/fs/nullfs/null_vfsops.c

Modified: head/sys/fs/nullfs/null_vfsops.c
==============================================================================
--- head/sys/fs/nullfs/null_vfsops.c	Wed Feb 29 15:18:04 2012	(r232304)
+++ head/sys/fs/nullfs/null_vfsops.c	Wed Feb 29 15:18:53 2012	(r232305)
@@ -185,7 +185,8 @@ nullfs_mount(struct mount *mp)
 		MNT_IUNLOCK(mp);
 	}
 	MNT_ILOCK(mp);
-	mp->mnt_kern_flag |= lowerrootvp->v_mount->mnt_kern_flag & MNTK_MPSAFE;
+	mp->mnt_kern_flag |= lowerrootvp->v_mount->mnt_kern_flag &
+	    (MNTK_MPSAFE | MNTK_SHARED_WRITES);
 	MNT_IUNLOCK(mp);
 	mp->mnt_data =  xmp;
 	vfs_getnewfsid(mp);