Re: xen/block.c: support unaligned writes

[Thomas Schwinge]

Hello again...

On Mon, Nov 16, 2009 at 10:59:11PM +0100, I wrote:
> On Mon, Nov 16, 2009 at 03:09:18AM +0000, Samuel Thibault wrote:
> > The branch, master-xen has been updated
> 
> > commit c4cbe430a3051382714fb9b38d551c5bba65291e
> > Author: Samuel Thibault <samuel.thibault@ens-lyon.org>
> > Date:   Mon Nov 16 03:22:44 2009 +0100
> > 
> >     Support unaligned writes
> 
> Great!
> 
> 
> One question about that one -- I'm not sure whether I asked you already
> on IRC some months ago and you told me that this is not possible or
> whether I didn't ask yet: as I understand the new code, in the unaligned
> case, you copy the *whole* data to align its beginning to a page
> boundary.  What about instead only copying that much from the source
> until you hit the next page boundary, enqueue that part (with its size
> being less than a page's size) for processing in the backend, and then
> enqueue the rest of the data, which now begins on a page boundary,
> without having to copy it any further?  Or aren't we allowed to split up
> one device_write request into two?

Jeez, I didn't think about simply asking my own documentation system...
<http://www.bddebian.com:8888/~hurd-web/open_issues/xen_crash_copy-size_le_page_size/>.
But does that really answer my question?


Regards,
 Thomas

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