On Mon, Aug 23, 2010 at 7:19 PM, Venkateswararao Jujjuri (JV)
<jvrao@xxxxxxxxxxxxxxxxxx> wrote:
>
> Eric Van Hensbergen wrote:
> > Is this just adding dead-code then? (I know I'm conflicting with my no
> > silent errors motto -- but I'm keen to keep our line-count down)
>
> Not really a dead code. if the O_DIRECT flag is set, __dentry_open() checks for
> f->f_mapping->a_ops->direct_IO before proceeding with open.
> In the absense of this routine, open with O_DIRECT flag fails.
>
> > By what path would we normally end up in this function? If caches were enabled?
>
> If cache is enabled we use generic_file_aio_read() as aio_read() operation.
> This ends up calling this new routine and fails with the error. So, until we
> actually
> implement a directio handle in the cached mode, there won't be a direct_IO support
> in the cached mode.
>
> generic_file_aio_read()
> {
> ...
> if (filp->f_flags & O_DIRECT) {
> ...
> ...
> retval = mapping->a_ops->direct_IO(READ, iocb,
> iov, pos, nr_segs);
>
> <<<The new routine returns error here >>>
> }
> }
>
> Will that be OK to move forwarded with directio support only for non-cached mode,
> and deal with cached mode later?
>
> Thanks,
> JV
>
Yup - seems reasonable enough - lets just make sure we remember it
when we get the cached modes in place. I guess this won't be a
regression even for existing cache modes because DirectIO would have
failed without the presence of this function anyways.
-eric
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