Re: [PATCH, RFC] ubd: remove use of blk_rq_map_sg

[Christoph Hellwig <hch@xxxxxx>]

On Wed, Oct 17, 2018 at 12:43:14AM +0200, Richard Weinberger wrote:
> On Mon, Oct 15, 2018 at 8:56 AM Christoph Hellwig <hch@xxxxxx> wrote:
> >
> > There is no good reason to create a scatterlist in the ubd driver,
> > it can just iterate the request directly.
> 
> BTW: Does it make sense to drop blk_rq_map_sq from()
> drivers/mtd/ubi/block.c too?
> If so we have to allocate a temporary structure for the worker thread
> for each segment, just like
> UBD does already. I'm not sure if that is cheaper than blk_rq_map_sq().

UBI should not need a new per-thread structure, mostly because there
are no threads involved.  The scatterlist support in UBI only seems
to exists for ubiblock, but it goes down a few layers.  In the end
all that could switch to a iov_iter-like setup and clean things up
a lot, but it would be a fair amount of work.

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