MFC 237518, 237545, 237648:

  r237518 | ken | 2012-06-23 22:29:03 -0600 (Sat, 23 Jun 2012) | 72 lines

  Fix a bug which causes a panic in daopen(). The panic is caused by
  a da(4) instance going away while GEOM is still probing it.

  In this case, the GEOM disk class instance has been created by
  disk_create(), and the taste of the disk is queued in the GEOM
  event queue.

  While that event is queued, the da(4) instance goes away.  When the
  open call comes into the da(4) driver, it dereferences the freed
  (but non-NULL) peripheral pointer provided by GEOM, which results
  in a panic.

  The solution is to add a callback to the GEOM disk code that is
  called when all of its resources are cleaned up.  This is
  implemented inside GEOM by adding an optional callback that is
  called when all consumers have detached from a provider, and the
  provider is about to be deleted.

  scsi_cd.c,
  scsi_da.c:	In the register routine for the cd(4) and da(4)
  		routines, acquire a reference to the CAM peripheral
  		instance just before we call disk_create().

  		Use the new GEOM disk d_gone() callback to register
  		a callback (dadiskgonecb()/cddiskgonecb()) that
  		decrements the peripheral reference count once GEOM
  		has finished cleaning up its resources.

  		In the cd(4) driver, clean up open and close
  		behavior slightly.  GEOM makes sure we only get one
  		open() and one close call, so there is no need to
  		set an open flag and decrement the reference count
  		if we are not the first open.

  		In the cd(4) driver, use cam_periph_release_locked()
  		in a couple of error scenarios to avoid extra mutex
  		calls.

  geom.h:	Add a new, optional, providergone callback that
  		is called when a provider is about to be deleted.

  geom_disk.h:	Add a new d_gone() callback to the GEOM disk
  		interface.

  		Bump the DISK_VERSION to version 2.  This probably
  		should have been done after a couple of previous
  		changes, especially the addition of the d_getattr()
  		callback.

  geom_disk.c:	Add a providergone callback for the disk class,
  		g_disk_providergone(), that calls the user's
  		d_gone() callback if it exists.

  		Bump the DISK_VERSION to 2.

  geom_subr.c:	In g_destroy_provider(), call the providergone
  		callback if it has been provided.

  		In g_new_geomf(), propagate the class's
  		providergone callback to the new geom instance.

  blkfront.c:	Callers of disk_create() are supposed to pass in
  		DISK_VERSION, not an explicit disk API version
  		number.  Update the blkfront driver to do that.

  disk.9:	Update the disk(9) man page to include information
  		on the new d_gone() callback, as well as the
  		previously added d_getattr() callback, d_descr
  		field, and HBA PCI ID fields.

  r237545 | ken | 2012-06-24 22:26:10 -0600 (Sun, 24 Jun 2012) | 7 lines

  Consume spare fields for the providergone pointers added to the g_class and
  g_geom structures in change 237518.  The original change would have broken
  the ABI.

  Suggested by:	ae

  r237648 | ken | 2012-06-27 10:05:09 -0600 (Wed, 27 Jun 2012) | 6 lines

  In g_disk_providergone(), don't continue if the softc is NULL.  This may be
  the case if we've already gone through g_disk_destroy().

  Reported by:	Michael Butler <imb@protected-networks.net>