It is possible to have raid1/4/5/6 arrays that do not use all the space on the
drive.  This can be done explicitly, or can happen info you, one by one,
replace all the drives with larger devices.

This patch extends the "SET_ARRAY_INFO" ioctl (which previously invalid on
active arrays) allow some attributes of the array to be changed and implements
changing of the "size" attribute.

"size" is the amount of each device that is actually used.  If "size" is
increased, the new space will immediately be "resynced".
Signed-off-by: Neil Brown <neilb@cse.unsw.edu.au>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>