In <sys/disk.h>, I note

        /*
         * Disk label information.  Storage for the in-core disk label
         * must be dynamically allocated, otherwise the size of this
         * structure becomes machine-dependent.
         */

This implies that someone thought the size of the structure was MI.
But this is false; it includes at least a handful of pointers, and thus
changes size depending on the arch's pointer size.

There also is no indication what would be wrong with struct disk
changing size depending on the MD things.

ISTM the comment, at least, needs updating.  Agree?  Disagree?  Anyone
know why having struct disk's size be MI was thought to be good?

/~\ The ASCII				der Mouse
\ / Ribbon Campaign
 X  Against HTML	       mouse@rodents.montreal.qc.ca
/ \ Email!	     7D C8 61 52 5D E7 2D 39  4E F1 31 3E E8 B3 27 4B