references to it.
This is the functional equivalent to change r237518, which added this
functionality to the cd(4) and da(4) drivers.
This fix prevents a panic caused by GEOM calling adaopen() while the device
is going away. We now keep the device around until GEOM has finished
cleaning up its state.
ata_da.c: In adaregister(), add a d_gone callback to the GEOM disk
structure registered for the ada driver. Increment the
peripheral reference count for GEOM.
Add a new callback, adadiskgonecb(), that GEOM calls when
it is done with its resources. This callback releases the
reference acquired in adaregister().
Submitted by: Po-Li Soong
Sponsored by: Spectra Logic
MFC After: 5 days