linux-kernel - Re: [PATCH] enhanced reimplemented of the kfifo API

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Date:	Fri, 15 Jan 2010 14:01:53 -0800
From:	"Ira W. Snyder" <iws@...o.caltech.edu>
To:	Stefani Seibold <stefani@...bold.net>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andi Kleen <andi@...stfloor.org>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Theodore Tso <tytso@....edu>
Subject: Re: [PATCH] enhanced reimplemented of the kfifo API

On Fri, Jan 15, 2010 at 10:30:01PM +0100, Stefani Seibold wrote:
> 
> > I'm glad to see this example, it really illustrates how to use the new
> > DMA functionality of the kfifo API.
> > 
> > Is there any reason why a very large scatterlist could not be used? I
> > have a driver that uses a large scatterlist (~4000 entries, allocated as
> > a struct sg_table). I implemented my own copy_from_user() functionality
> > into this scatterlist, but I'd love to use the kfifo DMA API instead.
> > After filling the scatterlist, I use the usual DMA API's to transfer it
> > to my device.
> > 
> 
> No, but the API will only return max. two entries.
> 

Ah, I see. __kfifo_alloc() uses kmalloc() internally. The kfifo API will
not work for my purposes then, since I want to allocate a 16MB chunk of
memory, and I'm very uncomfortable doing that with kmalloc(). I'll stick
with my custom scatterlist code, which uses alloc_page() to fill in the
scatterlist with order-0 allocations.

Another nitpick in the code: I've noticed that you use sgl++ in the
setup_sgl() function. That should become "sgl = sg_next(sgl);" so that
this code can work with an struct sg_table as well.

Thanks,
Ira
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