linux-kernel - RE: [PATCH] Cachefiles, mpage_cleardirty addtition, west bridge related

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Date:	Wed, 8 Sep 2010 14:20:06 -0700
From:	"David Cross" <david.cross@...ress.com>
To:	"'Christoph Hellwig'" <hch@...radead.org>
Cc:	<dhowells@...hat.com>, <linux-cachefs@...hat.com>,
	<greg@...ah.com>, <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] Cachefiles, mpage_cleardirty addtition, west bridge related



-----Original Message-----
From: Christoph Hellwig [mailto:hch@...radead.org] 

On Wed, Sep 08, 2010 at 09:51:22AM -0700, David Cross wrote:
> > This is used by the current west bridge driver in the linux-next tree,
> > marked as BROKEN at the moment. It is used in order to clear dirty pages
> > from the page cache for a specific file after it has been allocated.
This
> > allows west bridge to transfer data from USB to storage directly without
> > requiring that the file data path go through the CPU. The easiest way to
> > think of this is that it allows for direct file based DMA. Please let me
> > know if you have any additional questions or concerns on this.

> It's sad enough that it was taken into any tree at all, but we're not
> going to add incorrect crap into the kernel kernel for it.

Can you elaborate on what you mean by "incorrect crap" in a constructive way
if at all possible please?

> mpage_* are pagecache manpipulation routines, and are only for use by
> filesystems for inodes they manage.  A driver may never access this
> directly.

Then what about a user space call such as falloc()? Is your objection to the
existence of the code or the place where it is called from?

> Is this the same piece of junk you wanted fat_get_block
> exported for?

It is the same driver code, but I removed the fat_get_block call in a patch
that I submitted previously based on past inputs, instead adding a few lines
to this function.





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