mm and Oops

[Andries.Brouwer@cwi.nl]

After sending util-linux out, I booted a kernel that had kdev_t
a pointer type, to see whether that still works.
And all (minus md/lvm/nfs that didnt compile) was fine
except that kswapd produced an oops. Investigation shows
that it was caused by the combination of what <linux/swap.h> calls
"Ugly ugly ugly HACK" and what <linux/kdev_t.h> judges with "yuk".

So, maybe we must remove one or both of these sore spots.
The second one is the use of a special constant B_FREE
as device value to indicate that the buffer is free.
I'll look at this tomorrow but perhaps someone knows:
must the constant B_FREE (used only in fs/buffer.c) be nonzero?
If so, then we probably need a bitfield to indicate "free".
Otherwise we can use 0 ("no device") as value.

Andries