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


From: Roger Pau Monné
Subject: Re: [Qemu-devel] [Xen-devel] [PATCH 2/4] block/xen_disk: remove use of grant map/unmap
Date: Mon, 30 Apr 2018 16:28:26 +0100
User-agent: NeoMutt/20180323

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 <address@hidden>
> > Cc: address@hidden; address@hidden; qemu-
> > address@hidden; Anthony Perard <address@hidden>; Kevin
> > Wolf <address@hidden>; Stefano Stabellini <address@hidden>; Max
> > Reitz <address@hidden>
> > 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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