Proposed: changed to ramdisk driver

[Dale Rahn <drahn_(_at_)_diploid_(_dot_)_urbana_(_dot_)_mcd_(_dot_)_mot_(_dot_)_com>]

Notice of proposal for changes to the ramdisk driver.

Currently the ramdisk (rd) driver does not allow disklabels to be written
to the device. This causes problems with the new filesystem discovery
code for the root filesystem in dk_mountroot.

The proposal is to make the device respond more like a traditional device
where partition "c" is the raw partition as in "rd0c" and the other
paritions a-h or a-p are found in the standard disklabel manner.

This will allow the native label (fdisk,... and disklabel) or just a BSD
disklabel to be put on the disk image for mounting.
 
This will necessitate changes to the MAKEDEV of all archs that use
the rd device. This change will also affect how miniroot images are
created (files under src/distrib).
Also, now that the device is more of a real device a character device
should be assigned to the raw image of the disk
add to cdevsw: (src/sys/arch/{machine}/{machine}/conf.c)
	cdev_disk_init(NRD,rd),    /* X: ramdisk device */
and the appropriate change to chrtoblktbl or the appropriate character
to block mappings.

Do any problem other that the ones mentioned ?

I would like to make this change soon to be able to build working
md installation images from the checked in source tree.

Thanks

Dale