Re: [Xen-devel] [PATCH 2/4] block/xen_disk: remove use of grant map/unmap

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Roger Pau Monne
> Sent: 30 April 2018 16:12
> To: Paul Durrant <Paul.Durrant@xxxxxxxxxx>
> Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx; qemu-block@xxxxxxxxxx; qemu-
> devel@xxxxxxxxxx; Anthony Perard <anthony.perard@xxxxxxxxxx>; Kevin
> Wolf <kwolf@xxxxxxxxxx>; Stefano Stabellini <sstabellini@xxxxxxxxxx>; Max
> Reitz <mreitz@xxxxxxxxxx>
> Subject: Re: [Xen-devel] [PATCH 2/4] block/xen_disk: remove use of grant
> map/unmap
> 
> On Mon, Apr 30, 2018 at 01:01:37PM +0100, Paul Durrant wrote:
> > The grant copy operation was added to libxengnttab in Xen 4.8.0. If grant
> > copy is available then data from the guest will be copied rather than
> > mapped.
> > The xen_disk source can be significantly simplified by removing this now
> > redundant code.
> 
> Hm, I know this is a PITA, but FreeBSD gntdev hasn't implemented the
> grant-copy operation yet.
> 
> I could try to implement it, but I can't make any promises on the time
> ATM, since I'm quite busy.
> 

I guess we could carry a compat patch in QEMU that implements grant copy by 
doing a map/memcpy/unmap , but QEMU feels like the wrong place for that. I 
could try putting together a similar patch for the freebsd.c component of 
libxengnttab in the xen source rather than it simply failing with ENOSYS as it 
does now. Would either of those help?

  Cheers,

    Paul

> Thanks, Roger.

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