Invalidating buffer cache in dom0

[Jacob Gorm Hansen <jacobg@diku.dk>]

hi,

I have a domU that dumps some data (a checkpoint) to a virtual device. 
Afterwards, I want to create a new domU based on that data, but because 
right now my domain bootstrapper does not have a disk driver, I first 
build a ramdisk which I give as an argument to my bootstrapper.

This all works fine, but I have the problem that I have to reboot dom0 
between each run, because apparently dom0 Linux does not notice that the 
contents on disk have changed, and keep giving me stale data from its 
buffer cache when I create the ramdisk. I have tested that this is 
actually what happens by grepping for a string in the block device 
(/dev/hda5), and the value of the string changes between reboots.

Does anyone know of an ioctl or similar that I could use to make Linux 
forget about (not flush) buffer cache contents, or how to disable it?

I have tried reading from the block dev with O_DIRECT but that does not 
help.

Thanks,
Jacob