Re: [PATCH] [14/20] Don't disable direct_io for unchecked_isa_dma in st.c

[FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>]

On Fri, 14 Mar 2008 10:24:12 -0400
Christoph Hellwig <hch@infradead.org> wrote:

> On Fri, Mar 14, 2008 at 02:51:35PM +0100, Jens Axboe wrote:
> > Are you sure? Seems to me that st builds its own list with
> > get_user_pages() for direct io, where will that get bounced? The block
> > layer will only bounce things that are mapped directly, so if st used
> > blk_rq_map_kern() and inserted that request in the queue, we could
> > proceed with killing that check in st.
> 
> Which shouldn't be all too difficult and would be the right thing to
> do.  We really need someone to sit down and convert st/osst/sg to use
> the proper block layer helpers.

I've been working on this (hopefully, I'll submit an updated patchset
this week).

I think that the main problem was a lack of motivation for these
changes. I bet that nobody reviewed the patchset that Mike posted the
last time. Hopefully, the new patchset will be reviewed and merged.

With sg chaining, drain, padding, etc, building a scatterlist is much
complicated than in the past. I believe that we should kill home-made
scatterlist code and convert the users to use the block layer to avoid
potential scatterlist bugs.