How to create an image file system that grows

[T o n g <mlist4suntong@yahoo.com>]

Hi,

How can I create an image file system that can grow bigger as required?

Vmware, qemu, kvm, etc all can create file systems in an image file which 
is initially small, but grow bigger as required. I want to do that too, 
but 

 dd if=/dev/zero of=file-fs.ext2 bs=1k count=20k
 mke2fs file-fs.ext2 

would only create an image file initially as big as the full size.

please help, thanks

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Tong (remove underscore(s) to reply)
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