[Yaffs] "Formatting the flash"

Hello All
I have a query . Suppose at any point of time , the user wants to erase the complete flash, and restart( or in other words format the flash).

Now my idea is that ,this is not possible , at run time.
I presume we might have to use yaffs_unmount(), to deinitialise, YAFFS.But will it work to deinitialise all current directories and other objects??
Any suggestions as to how to go about a DiskFormat function if required??
Abhishek