Anyone who wants to know just how the MFS works need only read mfs_doio() in:

	src/sys/ufs/mfs/mfs_vnops.c.

It's a grand total of only _8_ lines, and it does all the MFS I/O by just
calling copyin() or copyout() to the mount_mfs process.

And that process is just the newfs process: see line 172 in

	src/sbin/newfs/mkfs.c

Which contains:

	membase = malloc(fssize * sectorsize)

Yes, the entire MFS is just a thing returned by a user program calling
malloc(3). The blocks will be created as they are touched.  They are never
released, but for the most part don't exist until used.


  -- Ross Harvey