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

[Alan Stern]

On Fri, 5 Sep 2003, Jörn Engel wrote:

> On Fri, 5 September 2003 14:49:15 -0400, Alan Stern wrote:
> > On Fri, 5 Sep 2003, Andreas Dilger wrote:
> > 
> > > 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.
> 
> Maybe these help you here:
> man 3 fdopen
> man 3 fileno
> 
> No filename needed for the second open.

I don't think they will help.  Apart from the fact that I'm working on a 
kernel module, not a user program, neither of these accepts options like 
O_DIRECT.

Alan Stern

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