O_DIRECT splice from PCI-resident buffer to filesystem

O_DIRECT splice from PCI-resident buffer to filesystem

[Steve Rottinger]

Hi,

After some work, and kernel hacking, and thanks to Jens'
O_DIRECT/blockio splicing
patch,  I have been successful in using splice to transfer data directly
from a buffer
resident on a PCI device to a raw disk partition, with zero copies. Great!
Can anyone tell me if it is feasible to transfer data in the same way,
using splice
to a file, on a filesystem, instead of a raw block device with zero
copies?   Looking at
the code, it appears that the data is copied using memcpy, no matter what.

Thanks,

-Steve

Re: O_DIRECT splice from PCI-resident buffer to filesystem

[Leon Woestenberg]

Steve,

On Fri, May 29, 2009 at 8:56 PM, Steve Rottinger <steve@pentek.com> wrote:
> After some work, and kernel hacking, and thanks to Jens'
> O_DIRECT/blockio splicing
> patch,  I have been successful in using splice to transfer data directly
> from a buffer
> resident on a PCI device to a raw disk partition, with zero copies. Great!
>

As we have no in-kernel character devices with splice_read/write
capability (other than /dev/null and maybe zero) *AFAIK*,
I would like to adapt my driver in staging/ to support splice_read()/write().

The difference is that my PCIe driver (altpciechdma.c) performs DMA
into a scattered set of pages. These pages are then
splice()d over.

Could you share the splice part of your driver for this purpose, so
that I can add splice_read() with less effort?

Regards,
-- 
Leon