/* * psref_acquire(psref, target, class) * * Acquire a passive reference to the specified target, which must * be in the specified class. * * The caller must guarantee that the target will not be destroyed * before psref_acquire returns. * * The caller must additionally guarantee that it will not switch * CPUs before releasing the passive reference, either by * disabling kpreemption and avoiding sleeps, or by being in a * softint or in an LWP bound to a CPU. */