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

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Mon, Apr 30, 2018 at 04:16:52PM +0100, Paul Durrant wrote:
> > -----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?

Maybe this could be implemented in gnttab_core.c, so it can also be
used by MiniOS and Linux versions not supporting the copy ioctl as a
fallback?

Roger.

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