Re: using O_DIRECT

[Bob McElrath <mcelrath+linux@draal.physics.wisc.edu>]

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Andrea Arcangeli [andrea@suse.de] wrote:
> On Mon, Sep 03, 2001 at 03:13:42PM -0500, Bob McElrath wrote:
> > I have written a small program to use O_DIRECT (attached), after
> > applying your patch o_direct-14 to kernel 2.4.9.  Opening the file with
> > O_DIRECT is successful, but attempts to write to the fd return EINVAL.
> > 
> > Am I doing something wrong?  Should I have to recompile glibc too?
> 
> eh, the alignment and size of the buffer have basically the same
> restrictions of running read/write on a raw device, with the only
> difference that for rawio the granularity is the hardblocksize, while
> for O_DIRECT the granularity is the softblocksize of the filesystem.

Ah, thanks, it's working now.  Makes sense that it should use blocksize
granularity...

> We'll have to relax the granularity of the I/O down to the hardblocksize
> for O_DIRECT too eventually.

I don't really care about the granularity.  The bigger the better,
actually, since I'm streaming data to disk quickly.  ;)

Thanks,
-- Bob

Bob McElrath (rsmcelrath@students.wisc.edu) 
Univ. of Wisconsin at Madison, Department of Physics

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