how can I ensure file reads go to disk rather than a buffer

[damon fasching <damon3937@yahoo.com>]

Hi,

Can somebody tell me how to ensure that when I read
from a file data is actually read from disk rather
than from a buffer?  I have studied both the low level
and stream I/O documentation at
gnu.org/manual/glibc-2.2.5. I have also done some
experimenting with both low level and stream I/O.

Basically, I want to write a chunk of data to a file
and then read it back to verify the integrity of the
data on disk.  The only function which looked
promising was __fpurge(FILE *), carefully applied. 
But I suspect that this function is only intended to
purge user level buffers, not kernel buffers, and so a
subsequent read would go to the kernel buffer, not
disk.

Suggestions?

Thanks!
  Damon


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