Re: How can I force a read to hit the disk?

[Andreas Dilger]

On Sep 05, 2003  13:46 -0400, Alan Stern wrote:
> My kernel module for Linux-2.6 needs to be able to verify that the media 
> on which a file resides actually is readable.  How can I do that?
> 
> It would certainly suffice to use the normal VFS read routines, if there
> was some way to force the system to actually read from the device rather
> than just returning data already in the cache.  So I guess it would be 
> enough to perform an fdatasync for the file and then invalidate the file's 
> cache entries.  How does one invalidate a file's cache entries?  Does 
> filemap_flush() perform both these operations for you?

If you open the file with O_DIRECT, it should read/write directly on the
disk, and it will also invalidate any existing cache for the read/written
area.

Cheers, Andreas
--
Andreas Dilger
http://sourceforge.net/projects/ext2resize/
http://www-mddsp.enel.ucalgary.ca/People/adilger/

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