[dm-devel] Re: [PATCH RFC 0/4] use scatter lists for all blockpc requests and simplify hw handlers

[Jens Axboe]

On Tue, Jun 07 2005, Tony Battersby wrote:
> > > My company (Cybernetics) sells several products that run embedded
> Linux
> > > which use the userspace scatter-gather capability of the SG driver.
> > > They are still running the 2.4 kernel series, but we will probably
> > > switch to 2.6 at some point.
> >
> > What do they actually use it for?  As in why is the data scattered
> even
> > in the virtual address space?
> 
> One of our products is a RAID-like controller for SCSI tape drives.
> Parallel SCSI or iSCSI in via a target-mode SCSI driver and parallel
> SCSI, iSCSI, or FC out via the SG driver, with various functions in
> between for data buffering, emulation, striping, mirroring, etc.  The
> program that controls everything has a complex internal buffering scheme
> that uses userspace scatter-gather for the main read/write I/O path to
> the tape drives.

That sounds like a valid use. Either way, I don't think we should remove
such a feature. It's a sane feature, and people might be using it -
there's no excuse for removing it.
Should we kill readv next? :)

-- 
Jens Axboe