Re-Partitioning without Rebooting?

[Andreas Schildbach]

Hello everyone,

I am trying to re-partition my harddrive without rebooting (of course I 
don't touch the partition I'm currently working on). However, everytime 
I am writing the modified partition table with fdisk, the following 
message appears:

--- snip ---

Command (m for help): w
The partition table has been altered!

Calling ioctl() to re-read partition table.

WARNING: Re-reading the partition table failed with error 16: Device or 
resource busy.
The kernel still uses the old table.
The new table will be used at the next reboot.
Syncing disks.

--- snip ---

Why is the device busy? How can I prevent the reboot?

Regards,

Andreas