Re: [PATCH] [13/21] Use blk_q_mask/get_pages_mask in sg driver

[Andi Kleen <andi@firstfloor.org>]

On Mon, Nov 17, 2008 at 02:11:51PM +0900, FUJITA Tomonori wrote:
> On Sun, 16 Nov 2008 23:17:22 +0100
> Andi Kleen <andi@firstfloor.org> wrote:
> 
> > On Sat, Nov 15, 2008 at 09:11:20PM -0500, Douglas Gilbert wrote:
> > > Andi Kleen wrote:
> > > >Instead of using GFP_DMA directly.
> > > >
> > > >Also I stubbed SG_SET_FORCE_LOW_DMA ioctls which don't make any sense
> > > >because the kernel should always use the correct values on its own.
> > > 
> > > You propose removing a define from a public interface and thereby
> > > might break existing code. A comment in sg.h might be appropriate.
> > 
> > Hmm, I assume those SG_SET_FORCE_* defines are only used 
> > in the kernel.
> 
> I don't think so. They are exported to userspace, the sg ioctl
> interface. There may be applications that use them.

I doubt it. For what would they use it? And when exactly
should an application know that some device has a 16MB
limit when the kernel driver doesn't know about that?

For me it looks more like a really old debugging interface.

> Well, I don't think that they are useful or a nice feature. They would
> become pointless when you finish your dma allocation rework. But I
> don't think that we can remove the existing API exported to userspace.

Ok I'll restore the defines. But readding the ioctls would
be messy. Do you really think that is needed? I would 
rather prefer to fix the driver to always GFP_DMA, but I am
not aware of any driver who needs it. Are you?

-Andi