linux-kernel - Re: [PATCH 2/6] shm: add sealing API

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Message-ID: <CANq1E4RWf_VbzF+dPYhzHKJvnrh86me5KajmaaB1u9f9FLzftA@mail.gmail.com>
Date:	Fri, 11 Apr 2014 02:22:13 +0200
From:	David Herrmann <dh.herrmann@...il.com>
To:	Tony Battersby <tonyb@...ernetics.com>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>,
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>
Subject: Re: [PATCH 2/6] shm: add sealing API

Hi

On Thu, Apr 10, 2014 at 11:33 PM, Tony Battersby <tonyb@...ernetics.com> wrote:
> For O_DIRECT the kernel pins the submitted pages in memory for DMA by
> incrementing the page reference counts when the I/O is submitted,
> allowing the pages to be modified by DMA even if they are no longer
> mapped in the address space of the process.  This is different from a
> regular read(), which uses the CPU to copy the data and will fail if the
> pages are not mapped.

Can you please provide an example code-path? For instance,
file_read_actor() does not pin any pages but only keeps the user-space
address and resolves it once it has data to write.

Thanks
David
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