Bug 25085

If /dev/mlx0 does not exist, 'mlxcontrol status' fails silently.  Because
/dev/mlx# is not created by sysinstall, a default FreeBSD install will have
device files for the disk and it's slices, but not the controller itself.

The error messages (or lack thereof) do not explain the problem easily.  I
only found it by running a ktrace on the process and watching it iteratively
try to open /dev/mlx0 through /dev/mlx63 and then exit.

Fix: 

- if a nonstandard piece of hardware is a viable install target, then
sysinstall and MAKEDEV should take that into account.  The mlx0 device
should probably be added to the standard devices to create upon
installation.

- mlxcontrol should perhaps test for the existence of the special file
/dev/mlx# instead of just attempting to open it and fail.  Additionally, if
the loop that tests mlx0-mlx63 expires without a successful open, a suitable
error message should be spit out.

- the points on device creation probably apply to some of the other RAID
for which drivers have recently been added: amr, ida.  There may not be a
userland control utility for either AFAIK, but the argument holds true for
anything that is in the GENERIC kernel, so...
How-To-Repeat: 
Install FreeBSD on a Mylex-equipped machine.  Immediately after install,
run 'mlxcontrol status'.  Now run 'mlxcontrol status mlx0'.  cd to /dev and
run './MAKEDEV mxl0'.  Repeat both of the commands.