Re: How to map high memory for block io

[Jens Axboe <axboe@suse.de>]

On Fri, Jan 27 2006, Pierre Ossman wrote:
> Jens Axboe wrote:
> > On Fri, Jan 27 2006, Pierre Ossman wrote:
> >   
> >> I'm having some problems getting high memory support to work smoothly in
> >> my driver. The documentation doesn't indicate what I might be doing
> >> wrong so I'll have to ask here.
> >>
> >> The problem seems to be that kmap & co maps a single page into kernel
> >> memory. So when I happen to cross page boundaries I start corrupting
> >> some unrelated parts of the kernel. I would prefer not having to
> >> consider page boundaries in an already messy PIO loop, so I've been
> >> trying to find either a routine to map an entire sg entry or some way to
> >> force the block layer to not give me stuff crossing pages.
> >>
> >> As you can guess I have not found anything that can do what I want, so
> >> some pointers would be nice.
> >>     
> >
> > Honestly, just don't bother if you are doing PIO anyways. Just tell the
> > block layer that you want io bounced for you instead.
> >
> >   
> 
> This is the MMC layer so there is some separation between the block
> layer and the drivers. Also, the transfers won't necessarily be from the
> block layer so a generic solution is desired. I don't suppose there is
> some way of accessing the bounce buffer routines in a non-bio context?

Only the mapping routines are appropriate at that point, or things get
complicated. You could still do a two-page mapping, if you are careful
about using different KMAP_ types.

-- 
Jens Axboe

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