Re: [RFC PATCH v2] lib: scatterlist: add sg splitting function

[Andrew Morton <akpm@linux-foundation.org>]

On Sat,  1 Aug 2015 15:17:13 +0200 Robert Jarzmik <robert.jarzmik@free.fr> wrote:

> Sometimes a scatter-gather has to be split into several chunks, or sub scatter
> lists. This happens for example if a scatter list will be handled by multiple
> DMA channels, each one filling a part of it.
> 
> A concrete example comes with the media V4L2 API, where the scatter list is
> allocated from userspace to hold an image, regardless of the knowledge of how
> many DMAs will fill it :
>  - in a simple RGB565 case, one DMA will pump data from the camera ISP to memory
>  - in the trickier YUV422 case, 3 DMAs will pump data from the camera ISP pipes,
>    one for pipe Y, one for pipe U and one for pipe V
> 
> For these cases, it is necessary to split the original scatter list into
> multiple scatter lists, which is the purpose of this patch.
> 
> ...
>
>  include/linux/scatterlist.h |   5 ++
>  lib/scatterlist.c           | 189 ++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 194 insertions(+)

It's quite a bit of code for a fairly specialised thing.  How ugly
would it be to put this in a new .c file and have subsystems select it
in Kconfig?