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

[Paul Durrant <Paul.Durrant@citrix.com>]

> -----Original Message-----
> From: Roger Pau Monne
> Sent: 30 April 2018 16:12
> To: Paul Durrant <Paul.Durrant@citrix.com>
> Cc: xen-devel@lists.xenproject.org; qemu-block@nongnu.org; qemu-
> devel@nongnu.org; Anthony Perard <anthony.perard@citrix.com>; Kevin
> Wolf <kwolf@redhat.com>; Stefano Stabellini <sstabellini@kernel.org>; Max
> Reitz <mreitz@redhat.com>
> 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.