Messages in this thread | | | Date | Fri, 5 Sep 2003 14:49:15 -0400 (EDT) | From | Alan Stern <> | Subject | Re: How can I force a read to hit the disk? |
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On Fri, 5 Sep 2003, Andreas Dilger wrote:
> 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.
Unfortunately that's not a good solution for me. The file has already been opened without O_DIRECT, and O_DIRECT wouldn't be appropriate because most of the time I do want I/O to go through the cache. It's just on a few rare occasions that I need direct access to the disk.
Maybe simply opening a new struct file using O_DIRECT, for purposes of the verification, while keeping the old struct file around for other uses later, will work? That would be awkward though -- and there's no guarantee that the original filename would still exist. It would be a lot nicer to do everything using the original file reference.
Alan Stern
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