Re: direct-to-BIO for O_DIRECT

[Douglas Gilbert <dougg@torque.net>]

Ingo Oeser wrote:

>On Sun, Jul 07, 2002 at 08:19:33PM -0700, Andrew Morton wrote:
> > Question is: what do we want to do with this sucker?  These are the
> > remaining users of kiovecs:
> > 
> >       drivers/md/lvm-snap.c
> >       drivers/media/video/video-buf.c
> >       drivers/mtd/devices/blkmtd.c
> >       drivers/scsi/sg.c
> > 
> > the video and mtd drivers seems to be fairly easy to de-kiobufize.
> > I'm aware of one proprietary driver which uses kiobufs.  XFS uses
> > kiobufs a little bit - just to map the pages.
> 
> It would be nice if we could just map a set of user pages to a scatterlist.

After disabling kiobufs in sg I would like such a drop
in replacement.

> Developers of mass transfer devices (video grabbers, dsp devices, sg and
> many others) would just LOVE you for this ;-)

Agreed. Tape devices could be added to your list.
Large page support will make for very efficient zero
copy IO.

> Block devices are the common case worth optimizing for, but character
> devices just need to reimplement most of this, if they want the same 
> optimizations. Some devices need mass transfers and are NOT blockdevices.

> Please consider supporting them better for 2.5 in stuff similiar to BIOs
> and DMA to/from user pages.

CIOs?

Doug Gilbert