svn commit: r206130 - head/sys/geom

[Andriy Gapon]

Author: avg
Date: Sat Apr  3 08:53:53 2010
New Revision: 206130
URL: http://svn.freebsd.org/changeset/base/206130

Log:
  g_vfs_open: allow only one mount per device vnode
  
  In other words, deny multiple read-only mounts of the same device.
  Shared read-only mounts should theoretically be possible, but,
  unfortunately, can not be implemented correctly using current
  buffer cache code/interface and results in an eventual system crash.
  Also, using nullfs seems to be a more efficient way to achieve the same
  goal.
  
  This gets us back to where we were before GEOM and where other BSDs are.
  
  Submitted by:	pjd (idea for checking for shared mounting)
  Discussed with:	phk, pjd
  Silence from:	fs@, geom@
  MFC after:	2 weeks

Modified:
  head/sys/geom/geom_vfs.c

Modified: head/sys/geom/geom_vfs.c
==============================================================================
--- head/sys/geom/geom_vfs.c	Sat Apr  3 08:39:00 2010	(r206129)
+++ head/sys/geom/geom_vfs.c	Sat Apr  3 08:53:53 2010	(r206130)
@@ -161,6 +161,10 @@ g_vfs_open(struct vnode *vp, struct g_co
 	g_topology_assert();
 
 	*cpp = NULL;
+	bo = &vp->v_bufobj;
+	if (bo->bo_private != vp)
+		return (EBUSY);
+
 	pp = g_dev_getprovider(vp->v_rdev);
 	if (pp == NULL)
 		return (ENOENT);
@@ -176,7 +180,7 @@ g_vfs_open(struct vnode *vp, struct g_co
 	vnode_create_vobject(vp, pp->mediasize, curthread);
 	VFS_UNLOCK_GIANT(vfslocked);
 	*cpp = cp;
-	bo = &vp->v_bufobj;
+	cp->private = vp;
 	bo->bo_ops = g_vfs_bufops;
 	bo->bo_private = cp;
 	bo->bo_bsize = pp->sectorsize;
@@ -196,5 +200,6 @@ g_vfs_close(struct g_consumer *cp)
 	gp = cp->geom;
 	bo = gp->softc;
 	bufobj_invalbuf(bo, V_SAVE, 0, 0);
+	bo->bo_private = cp->private;
 	g_wither_geom_close(gp, ENXIO);
 }