makefs/zfs/tests: Force-destroy md devices

Most of these tests create a md(4) device backed by a makefs-generated
image, then import the pool, using the md device as a pool vdev.  When
a test finishes, it destroys the pool, then destroys the md device.

Once in a while md device destruction fails with EBUSY.  This happens
when a GEOM consumer is holding the device open; kern_mddetach_locked()
simply fails if any consumers are present.  zpool destruction is
synchronous so ZFS is innocent, rather, the problem seems to be that
GEOM re-tastes the device after the zpool reference goes away.  This
operation creates a transient reference that causes the spurious
failure.

Use "mdconfig -o force" to work around this.

MFC after:	2 weeks

0 files changed, 0 insertions, 0 deletions