[PATCH 2/6] shm: add sealing API

[David Herrmann]

Hi

On Thu, Apr 10, 2014 at 11:33 PM, Tony Battersby <tonyb at cybernetics.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