Determining actual flash usage of a particular file

[419cf994 at tempmail.wgz.org]

I've been reading through the archives for several days, so I hope I 
haven't missed an answer somewhere.

Is there a way to determine the actual flash space occupied by a 
particular file on a JFFS2 partition?  'ls' and 'du' report number of 
bytes of the content of the file, but of course compression and other 
factors affect that greatly.

My definition of actual space is flexible...  could be number of blocks or 
pages occupied, or something similar.  I just need a metric that's more 
closely related to storage space than uncompressed size.