Checkpoint unloading fix

[Matthew Dillon]

:I have written a small patch that should remove the possiblity of a process
:being checkpointed when the check point module is being unloaded.
:Not quite for about it, so if anyone have some feedback I would be grateful.
:
:http://eirikn.kerneled.org/dragonfly/checkpoint_unload.patch
:
:-- 
:Eirik Nygaard

    Almost looks good... you can't infinite-loop in MOD_UNLOAD, you will lockup
    a UP system.

    I recommend causing the MOD_UNLOAD to fail if chptinuse is non-zero.  Return
    EBUSY:

    case MOD_UNLOAD:
	if (chptinuse) {
		error = EBUSY;
		printf("ckpt in progress, unable to unload ckpt module\n");
	} else {
		register_ckpt_func(NULL);
		PRINTF(("ckpt unloaded from %d\n", chkpt_offset););
	}
	break;

					-Matt
					Matthew Dillon 
					<dillon at xxxxxxxxxxxxx>